:
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The Behavior
Volatù'e "'atty Acids in
Model Solution duririg "'reeze-drying
\
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.1
Dav id W.
cpeak
.Submitted to the l-'aculty of Graduate Studies and
Research, McGill University, in partial fulfillment of the
requirements for the degree of Master of Science
,.
School of "'ood Séience
Macdonald College of McGill University
Ste. Anne de Bellevue, Que bec
•
M.Sc.
FoOd Science
ABSTRACT
Thé Behavior of Volatile Fatty Acids in Model
Solutions during Freeze-Drying
David W. McPeak
The
retention of
acetic,
propionic,
but·yric,
isovaleric
and'valeric acids was monitored in aqueous solutions of pectin,
~
,
gelatin, corn syrup sol ids and gum arabic after freez)-drying •
,-
A decrease
of
acidity
SOlution~d hydro-
in both aqueous
colloid solutions, promoted larger populations of fatty acids
.,-
in the
non~volatlle,
increase
_addit~on
in
the
ionized
amount
of
form and consequently led to an
fatty
aci'd
being
retained.
of sucrose to pectin, gelatin and gum arabie
enhanced the retention of volatile
The
50l~tions
-
fatty adds;
whereas,
the
addi tion of glycine and phthalate deereased the retention of
fatty acids
solide.
in
solutions of
pectin,
gelatin
The addition of sodium ehloride or calcium chloride to
any of the hydrocolloid solutions also
reduced~the
'\
volatile fatty acids.
in hydrocolloid
-'
retention of
1
Volatile retention was shown to increase
solutions
t-li
th an
size of the volatile fatty acids.'
both
and corn syrup
increase
in
the molecular
These results suggested that
the molecular size of the volatile and the vi,scosity of
the hydrocolloid solutions influenced volatile retention.
In
addition,
of
froze,n
sol utions
exper ienced
slight
losses
volatile fatty acids during short-term frozen storage.-
-_ _-(--....
-
~-_ ... _~----
,
".Sc.
.
Science d'alimentation
RESUME
Le comportement des acides gras volatils dans des
solutions modèles durant la l'yophilisation
1
Dav'id W. McPeak
La
rétention des acides acét'ique, propionique,
isovalérique,
et
valérique
a
été
suivie dans
b1Jtyrique,
dGS
solutions
aqueu,ses de pectine, de gélatine, de solides de sirop de mais,
et
1
de, gomme
acidit~
1
a
d'arabique
..
lyophilisation.
apres
'été diminuée dans des solutions
Lorsque
aqueuses
et
l'
des
solutions contenant des hydrocolloid-es, ceci a provoqué une plus
grande quantité d'acide en
'p'ar conséquent a favorisé
"
gras.
L' addi tion de
gélatine,
acides
de
gras
gomme
forme
saccharose
0,
et
non-volatile,
un plus forte rétention des acides
aux solutions de pectine,
d' arabique
volatil
ionique et
mais
a
la
amélioré
présence
la
de
rétention
glycine
de
des
et
de
phthalate ,a diminué la rétention dans des solutions de pectine,
.de
gêlatine,
et de
solides
de
sirop de mais.
J
plus,
De
la
.
presence de chlorure de sodium et de chlorure de calcium dans
toutës solutions contenant des hydrocolloides a rédui t
tion des acides gras volatils.
la réten-
La rétention des volatils dans
des solutions contenant des hydrocoll ides a augmenté lorsque la
taï 11e des molécules
r~sultats
que
viscosi té des
la
s'est
taille
agrand ie.
moléculaire
On peu t dédu i re de ces
des
volatils
et
la
solutions contenant des hydrocol19ides Jouent un
rnle dans la rétention volatile lors d'une brève congélation.
1\
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1
1
1
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AC~DGEKENTs
,
11
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The author wLshes to thank Dr. T. G. Smyr
1
Idziak for their ~dvice and encouragement given th
course of this work and the writing of this thesis.
"
The author also wishes to thank the following
for
their
help:
Dr. ~.R. van de Voort for his co-operation and guidance in
the operation of the infra-red spectrophotometer
Mr. Guy Thibault for his co-operation in the operation of
the scanning electron microscope
Miss R. Murray for her assistance in typing this thesis
"
The
support
of
the
Nat ural
Science
and
Research Council of Canada is a1so acknowledged •
..
,
-._--'- - -
,
~,
_. -.. - --' '--
-- -' ... ,---------.-. --_...
"~."-''''""
Engineering
..
..,.
Suggested short title:
;.,.~
Volatile r'atty Acid Retention during
,
,\,
.
'"
l-'reeze-drying
,
McPeak
,
,
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page
.......................... .............. .
1
•
II. LITERATURE REVIEW .....................................
4
A. Introouction ..•.. .~ .............................. ~ .. .. .
4
B. Kechanisms for Volatile Loss during
Freeze-drying ..............•...........•......• . ' ..
1) The Eutectic Melting Theory •••••••••••••••••••
il) The Amorphous Viscosity Theory ••••••••.•••••••
4
5
6
1., INTRODUCTION
'
C. Kechanisms for Volatile Retention during
Freeze-dryinq .........-: ......................
t ......... .
10
, i) Selective Diffusion ••••••••••••••• J. ..... ... .
ii) Kicroregion Entrapmen~ Theory ••••••••••••••••
Ui) Adsorption and Inclusion •••••••••••••••••••••
20
D. The Effect of Processing Conditions on
volatile Retention during Freeze-drying •••••••••••
24
i)
Freez ing Rate .........................................'.
i i) Sample Dimensions ••••••••••••••••••••••••••••
iii) Drying Rate ........................' .................... .
iv)
v)
vi)
vii)
11
16
25
26
27 '
Solids Composition •••••••••••••••••••••••••••
Solids Concentration ••••• ~ •••••••••••••••••••
Initial Volatile Concentration' •••••••••••••••
Type of Vo~atile •••••••••••••••••••••••••••••
34
III. MATERIALS AND METHODS •••••••••••••••••••.••••.•••••••
36
................................................
36
B. Equ i pmen t o • • • • • • • • • • • • • • • • • • • " . . . . . . . . . . . . . . . . . . . .
i) Freeze-Oryer ......••••••••••••••.• ;..........
38
38
~~,
A. Chemicals
ii) Gas Liquid Chromatograph •••••••• ~~•••••••••••
38
".~...........
39
iv) Scanning Electron Microscopy •••••••••••••••.•
v) Infra-Red Analysis •.••••••.••••••••••••••••••
39
40
Sample preparation .......•.•..........•........ "..
i) Effect of Sollds Composition on
41
iii) pB Meter •••..••••.••••••••••••
c.
28
32
33
Volatile Retention ••••••••••••••• ~ ••••.••• ~ ••
ii) Effect of pH and Ionie Strength on
Volatile Retention .............................
iil) Effect of Type and Amount of Volatile
on Volatile Retention .................. ,• .'.......
iv) Effect of Calcium Chloride (CaCl2) and the
Rate of Freezing on Volatile Retention •••••••
41
42
43
44
•
page
Table of Contents (continued)
'~
.........................
4S
E. Fatty Acid Analysis ••••••••••••••••••••••••••••••
45
F. Statistieal Analysis .•• : ••••••••••••••••••••••••••
46
RESU~TS
47
D. Freeze-Drying of Samples
•
IV.
AND DISCUSSION •••••••• "••••••••••••••••••••••
i) Introduction .............................••.••. .
ii) Effeet
Solids Composition on the
of
47
Retention of Volatile Fatty Aeids ••••••••••••••
lii) Effeet of pH and Ionie Strength o~ the
Retention of· Volatile Fatty Aeids ••••••••••••••
iv) Effect of Type and Amount of Volatile on
the Retention of Volatile Fatty Acida ••••••••••
v) Effect of Calcium Chloride (CaCl2) and the
Rate of Freezing on the Retention of
Volatile Fatty Acids •• ~........................
9S
V. SUMMARY AND CONCLUSIONS •••••••••••••••••••••••••••••
102
..........................................
105
\
VI.
REFERENCES
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56
74
85
,
,
LIST OF TABLES
.~
Page
TABLE
, 1~
2
3
Corn syrup solids composition.
48
Reténtion of volatile fatty adds (C2-CS) ~n,
pectin solutions after freezing and storage at
-20·C for 24 h.
53
,.
•••' •••••
;
.............. .
'Retention of volatile fatty acids in gelatin
solutions after freezing and storage at -20"C for
24 h. • ........ ~ • • • • • • • • • • • • . • • • • • . . • • • • . • . • • • • • • •
54
Retention of volatile fatty adds (C2-Cs) in
solutions of corn syrup soHds after freez i ng, and
storage at -20·C for 2:4 h ••~ •••••' ••••••••••••••••
5S
Retention of ~olatile fatty acids (C2-CS) after
freeze-drying 'in pectin solutions containing
addi tional solute. . ............................ .
57
Average retention of volatile fatty acids (C2-CS) "1
after freeze-drying solutions of gelatin, corn
syrup solids and gum arabie eontaining, addi tional
solute ............. _/* ............................ *__
59
,
5
6
7
37
Linear regression parameters for standard curves
of volatile fatty acids (C2, C4, 'CS) in solutions
of pectin (3' wt/wt), gelatin (3' wt/wt} and eorn
syrup soHds (5' wt/wt) ••••••••••••••••..•••.•••
1• • • • • • • • •
4
................ ,. .
- 1
,
8
9
.10
--".
\
11
Average retention of volatile fatty acids after
freeze-drying aqueolis solutions adjusted for pH
by a phthalate buffer. • •••••••••••••••.•••••••••
75
Average retention of 'volatile fatty acids (C2-CS)
after' ~-treeze-drying pectin solutions (3% wt/wt)
, adjusted for pH, and sodium chloride. • ••••••..•••
77
Average retention of volatile fatty acids (C2- CS)
after freeze-dryi'ng g.elatin solutions {3.%. wt/wt}
adjusted for pa and sodium chloride ••••.••••••••
Solubility
and
dissociation
constants
78'
for
:~i~~~~~~~ ~~~~: ... ~~~?~ ... ~ :::~~~ ... ~~ ... ~:~~~~~
"
79 .'
1
1';' •
,.
12
Ave~age
retentwn of volatile fatty aeids (C2-CS)
in solutions of corn syrup soUds (5% wt/wt)
adjusted for pB and sodium chloride . . . . . ~ ........ .
1
\
83
-
,
,
~
13
14
lS
16
17
,
87
~
Retention of butyric acid after freeze-drying
pectin solutions (3% wt/wt) containing valerie
aeid as additional volatile. • •••••••••••••••.•••
88
Retention of- butyrie acid
solutions of
corn syrup
eontaining
valerie
acid
volatile.
...................................... .
89
Retention of butyric acid after freeze-drying
solutions
of
peetin
(3%
wt/wt)
containing
volatile fatty acids as addi tional~ volatile.s. • ••
91
Retention of butyric acid after freeze-drying
sol u t ions
of
corn syrup
soUds
( 5 % wt/wt)
/ containing volatile fatty acids as additional
vola t i les #-. ••••••••••••••••••••••••••••••••••••••
92
.
- .,.
19
20
''\
Retention of volatile fatty acids (C2-CS) after
freeze-drying solutions of pectin (3% wt/wt),
gelatin (3\ wt/wt), gum' arabic (3% wt/wt) ,and
corn syrup solids (5% wt/wt) ••• :'••••••••••••••••
.
after freeze-drying
soUds (5% wt/wt;J,..
as
an
additional
Average retentiori of volatile fatty aeids (C2~CS)
after freeze-drying pectin solutions (3% wt/wt)
containing calcium ehloride frozen at different '\
rates ..................
.
-
18
Il'
Page
TABLE
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.1 • • • • • • • • • • • • • • • • • • • • • • • • • • •
96
Average retention of volatile fatty acids (C2~Cs)
after freeze-drying gel~tin solutions (3% wt/wt)
containing calciym chloride frozen a,t diff~ent
rates . . • . . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . .... ~ ...
97
Average retention of volatile fatty acids (C2-Cs)
after freeze-drying solutions of corn syrup
solids (5% wt/wt) eontaining calcium chloride
frozen at different rates •••••••••••••••••••••.•
98
.
.
-
~.,\
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.'
o~
1
~
,
0
.
l'
LIS'!' OP FIGURES
Page
FIGURE
Standard curve for volatile fatty acids (Cl' C4,
CS) in pectin solutd.ons (li wt/wt). •••••••••••••
2
3
4
6
..
8
9,
49-
"
Standard €urve for volatile fatty acids (C2, C4'
CS) in gelatin solutions (3% wt/wt) •••••.•••.•.•
50
Standard curve for volatile fatty acids (C2, C4'
CS) in solutions of corn syrup solids (5% wt/wt).
51
Scanning electt'oFl microqraph of a freeze-dri ed
solids matrix containinq pectin (1% wt/wt) and
sucrase (2% wt/wt). • ............................ .
62
Scanning electron micrograph of a freeze-dried
solids matrix containinq gelatin. (;h wt/wt). . •••
62
Scanning eleetron micrograph of a freeze-dried
sO,lids matrix eontaininq qum arabie (3% wt/wt).
63
Scanning electron microqraph of a freeze-dried
solids matrix containing pectin (1% wt/wt) and
glyc ine (2% wt/wt). • •••••••••••••••••••••••••.••
63
Scanning eleetron microqraph of the platlet
surface from a freeze-dried solids matrix
.ÇÔntaining pectin (3' wt/wt) and valerie acid (,%
. v<?l/vol) ................................. " • • • • .. • • . .
~
Scanning e~ectron ,mieroqraph of the platlet
.urface trom a freeze-dried solids matrix
cqntaininq qum Arabie (3% wt/wt) and valerie acid
( vol/vol).
Il....................................
,
.'
,.
<f'
'
10
Infra-red spectrum of water
11
Infra-red spectrum of a pectin solution
12
Infra-red spectrum
13
Infra-red spectrum of a peetin solution (6% wt/wt)
14
Infra-red spectrum of a solution containing
pectin (6% wt/wt)'and sucrose (12~ wt/wt) •••.••••
15
. ,,
pf
(5.0-10~)
67
wt/wt)
68
a pectin solution (4% wt/wt)
69
Infra-red spectrum of a solution eontaining
pectin (6% wt/wt) and phthalate (12% wt/wt).
.....
\\
70
71
72
,
"
1
65
•••••••••••
(~%
64 ,
.....
~..
..
..
-
--
-
_~
. - . _ ....
______
- _ ...... _
..
~
- ' _ _ ....
_
,
• a
.....
paqe
FIGURE
16"
17
Infra-red spectrum of a" solution containinq
pectin (6' wt/wt) and glycine (12% wt/wt). •• ~ •• "
73
Retention of volatile fatty ~~ids (C2-CS) in
solutions of pectin (3% ·wt/wt), gelatin, (3'
wt/wt), and corn syrup solids'(S% wt/wt) buffer~d
to different pH values .•••••• ; •••••••••••••' •••••
81
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1.
ItrrRODOCTION
\
One of the major reasons
stuffs
is
to extend
for
the dehydration of food-
the shelf life of perishable
foods
by
., ..
lowering
~t
Many of the conventional drying processes such as air, drum,
the water activi ty
through
the
rernoval of
water •
~'
"
and
freeze-drying
have
been
successfully
commercial dehydration of both solid and
adapted
to
liquid fooas.
the
The
commercial success of these drying techniques is partly dependent on their abili ty ',to retain nutrients,
' 1 ~"',
flavor'and aroma upon rehydration.
tics
•
are especially
foods
such
as
important
$OUP mixes,
coffee (Karel, 1975).
in
fruit
texture,
color,
Such quality characteristhe dehyd':ation of
juices,
milk
liquid
products and
Spray drying i5 widely applied to the
commercüil dehydration of skim milk and fruit
juices because
it is a relatively energy efficient process.
Al though the
'.
energy requirements are higher for
to
ai,r
and
superior
spray
flavor
drying,
a
fre~ze-drying
freeze-drled
produc~
and aroma characteristics upon
Other advantages of freeze-drying include:
in comparison
exhibi ts
rehydration.
a reduction in the
rates of degradative reactions occurring during drying'due to
the low temperature used;
an absence of. .the
case hardening
phenomenon due to a reduced migration of dissolved solutes by
capillary liquid flow;
due
\
to
a
lack
of
and less physical
spattering
or
liquid
1055
of the product
entrainment
during
dehydration (King, 1971).
To date, MOSt of the experimental work published on the
behavi9r of volatile substances during freeze-drying has deait
- 2 -
with
proces8
•
However,
conditions
addltional
which
enhance
information
is
volatile
required
retention •
concerning the
influence of solutioft properties on volatile retention during
freeze-drying.
Solution properties
strength vary in both
Furthermore,
influence
the
natural and
removal of
such
as
pH
formulated
water
during
solution properties and affect
and
food
ionic
systems.
dehydration will
the performance of
the product upon rehydration.
In this study the retention of a homologous series of
volatile fatty acids
different
(C2-CS)
was
studied as
à
function of
chemical properties ln model solutions.
Volatile
fatty acids o,cur naturally in foods such as leafy vegetables
and dairy prOducts.
Fatty acids also oceur as a result of
post-harvest spoilage in both animal and seafood products.
addi tion,
volatile fatty acids will chelate metals,
In
control
->.
microbial
growth,
decrease
enzymatie
flavoring components in food systems.
activity,
and
aet
as
These fatty acids will,
by their chemical nature, change solution properties such as
pH
through their dissociation to the ionized forme
Bence, the
retention of volatile fatty acids was examined in model solutions in order to predièt their behavior during freeze-drying.
The model solutions were prepared with bath hydrocolloids
and low-molecular weight solutes.
The hydrocolloids used in
th!s study are common components of many food systems.
They
oecur in both natural foods such as fruits and vegetables, and
in fomulated foods such as
--- ...
j~s
and comminuted meats.
The
•
'chemical nature of these hydrocolloids will also be influenced
by the solution properties and affect the retention of vola-,
.... ~e fatty acids, .. during freeze-drying.
Both sugars and salts
are known to bind water anq hence affect gelling properties i~
pectin
and
sugars and
gelatin
saI ts
systems.
Furthermore,
to solutions that
add a flavor and aff,ect the texture of
are
the
add i t iOI} of
freeze-dried,
will
the product upon rehydrar,
tl'on.
solutes
effect
In thls
to
on
stu~y,
the addition of lowi molecular weight
hydrocolloid
the
solutions
retention
freeze-drying.
1
•
·1
•
1
of
was
volatile
evaluated
fatty
for
acids
their
during
\,
1 _
-,
- 4 -
Il.
LI'l'BRA'1'ORE RBVI BW
A.
Introduction
,1
Freeze-dTled coffee has captured a substantlal portion of
its market value due to superior aroma retention and 900d
rehydrati~n
characteristics.
\
,
food
systems
such
as
However, there are freeze-drie4
fruit
juices
which
show
both
poor
rehydration characteristics and poor aroma retention (Bellows
and
J(~n9;
1972; 1973).
In an effort to improve volatile retention, the effect of
different process conditions has been
evalu~ted
by monitoring
volatile retention during freeze-drying (Thijssen and Rulkens,
1968~'
Fllnk and Kar91, 1970b).
This type of information has
enabled investigators to develop models which explain aroma
•
retention
and
to
ensure
i ts
optimization
during
the
freeze-dryifig process.
B.
Mecbanisas for volatile 108S during
The sublimation of water
during drying 15
. occur via capil1aries formed during
matrix
(King,
1970).
King
freeze-d~in9
(1970)
thought to
freezing of the 801ids
defined portions of the
801ids matrix which 'rave not reached the dried state as the
concentrated amorphous solution (CAS).
The graduaI constric-
tion of capillaries occurring in the solids matrix during the
removal of water was described as structural co11apse (Bellows
and King, 1973).
The constriction of capillaries occurred as
,
~
,
- 5 ..
a result of the flow'of CAS aince the
been reached.
fin~
dry state had not
The collapsing capillary reduces the permeabil-
')
ity of the water vapor and results in water being removed by
-'i<,
"
.
evaporation.
In
addition,
volatile
105s
would
occur
with
entrainment of water and puffing of the solids during evaporation.
Bellows and King
,
(1973) estimated the amount of vola-
tile 1055 due to structural collapse by relating the extent of
puffing to aroma retention in freeze-dried sucrose solutions.
In order
to explain the physical phenomenon occurring,
both
the eutectic melting theory and the amorphous theory have been
used
to
describe
structural
These
collapse.
theories
are
discussed below.
i)
The Eutectic Melting Theory
Bel~ows
and King (1973)
reported that when binary solu-
tions are cooled below their eutectic temperature, a eutectic
. mixture of ice and solute crystals forms.
drying the temperature of the
If during
freeze-
frozen mixture is raised above
ttre eutectic tempe rature , portions of the frozen matrix dissolve and the matrix eventually collapses due to the forces of
surface tension and gr.avity.
supported by
~to's
The eutectic meltlng theory is
(1970) previous observations on structural
collapse in solutions of sodium chloride and other salts when
held
above
their
eutectic
temperature
during
freeze-8rying.
Volatile loss occurs as a result of "bubbling and spattering of
the solids matrix due to water removal by evaporation.
..
- 6 -
(
ii) The Amorphous Viscosity Theory
In
frozen
solutions
wher~
a
eutectic
mixture
is
not
formed, structu~al cqllapse is dependent on Othe viscosity of
the CAS formed during freezing (Beliows and King, 1973).
The
temperature (Tc) at which structural collapse occurs was preforces (2fl
dicted in terms of surface, tension
acting at the
surface of open capillaries, the viscosity of the
cAs
(p), and
the radius of the capillary (R).
(1)
This equation e,stimates' the order of magnitude for CAS viscosity that
dence
.
i5 required to prevent; collapse.
which
supports
the
viscosity, was reported
fo~
predic,ted
Exp~rimental
magnit~de
for
ev i-
collapse
both fruit juices and model s01u-
tions (Bellows and King, 1972; 1973).
When the temperature of the
frozen matrix is held below
the collapse temperature, the solute matrix is viscous enough
to act as a solid.
As the temperature increases, melting and
dilution of CAS causes co1lapse of the matrix.
Collapse tem-
peratures were observed to increase in solutions prepared with
solutes
of
increasing
molecular
weight
(MacKenz ie,
1965:
Bellows and King, 1972; 1973, Tsourouflis et al., 1976: To and
'\.'link, 1978b).
The addition of 10\" molecular weight solutes
such as sodium chloride, dimethyl suHoxide, and glycerine to
sucrose solutions decreased the collapse temperature by thermodynamically lowering both the viscosity and the equilibrium
l
J
/
- 7 -
CAS concentration.
Conversely, when large moleèules such as
pec~in
gelatin
and
were
added
ta
sucrase
solutions,
an
increase
in the collapse ternperature was observed due to an
-1
increase in CAS
The
.'
,
t.
vi~cosity
collapse
decreased
when
the
increased
from
15
However,
sidered
(Bellows ànd King, 1973).
temperatures· of
initial
to
55
frozen
sucrose
~oncentrations
wt%
(Bellows
of
and
solutions
sucrose
King,
this deerease in eollapse tempe rature was
important when eompared
temperature caused
solutes.
I\n
by the
'.oIere
1973).
not con-
to the decrease in collapse
addition of
low rnolecular weight
inerease in solids concentration produced less
internaI surface in the solids matrix sinee less void space i6
present.
The
reduced
internal
surface would decrease
the
amount of surface tension required for eollapse.
The collapse
temperature
shown
of
dry
binary
solute
systems
was
to
be
dependent on the weight fraction and collapse temperature of
eaeh
pure
eomponent.
To
and
F link
(197Bb)
predicted
the
col..,1apse temperature of a binary solution given the collapse
temperatures (Tc) of the solutes and their ~eight fractions by
the foilowing formula:
where Tc are degrees absolute,. W i5 weight fraction,
B is a
constant and the subscripts 1 and 2 denote the two solute components
in
the
mixture.
collapse temperature were
The
experirnental
values
for
the
in agreement wi th predicted values
for maltodextrin (Maltrin 150) solutions prepared with different weight fractions of maltose
(TO and Flink,
1978b).
In
--
- 8 ,',
contrast, a graduaI
increase in the coIIapse temperature was,
not obse~ved when either Karaya or Tragacanth gum was added'to
orange juice.
A smaii amount of Karaya gum (0.5 wt\> elevated
the collapse temperature of orange juice from 52 to 67·C.
collapse temperature
The
then remained. constant over the concen-
tration range of 0.5 to 4.0 wt%.
behavior as Karaya gum,
Tragacanth gum showed similar
but the elevation of the collapse
temperature was much higher (Tsourouflis et al., 1976>.
When
humidified
maltodextrin
to
samples
increasing
levels
were
of
freeze-dried
moisture
•
and
content,
then
the
collapse temperature was observed to decrease (Tsourouflis et
al., 1976).
Bellows and King (1973) related mQisture content
to the viscosity range during' which the collapse of sucrose
and maltose sampI es occurred.
ted
that
col1apse
linearly dependent.
To and Flink (1978b) demonstra-
temperature
and
moisture
content
These authors suggested that during
were
the
humidification of freeze-dried samples, water molecules would
break
hydrogen
bonding
between
freeze-dried matrix to collapse.
the
solids
and
cause
the
In an attempt to describe
the effect of hydrogen bond breaking on mechanical strength,
.
Nissan (1976) related moisture content to Young's modulus.
TO
and Flink (1978b) suggested that both collapse temperature and
Young 1 S
na~ely
modulus
were
measuring
the
same
structural
force,
hydrogen bonding.
The
changes of freez ing rate, heat transfer geometries,
and the formation of a surface layer were examined to deter-
-- .. _-- .. -----
- 9
mine
their effects on
samples.
sampl~s
The
collapse
cOllapse
temperature
temperature of
in freeze-dried
freèze-dried
maltose
was found to be independent of the heating rate (TO
and FUnk,
1978a).,
Changes in the freezing rate produced no
detectable
changes
in
sucrose solution.
freezing
and
freeze-dried
the collapse temperature of a
The
changes
matrix
formation of a
in
were
heat
surface
transfer
shawn
ta
25 wt%
layer
geometries
decrease
the
during
in
the
collapse
temperatùre (Bellows and King, 1913).
Carbohydrates
are
dried
from
an
aqueous
either an amorphous or a crystalline state.
solution
in
Flink and Karel
(1972) have demonstrated the importance of the amorphous state
;
on the retention of propanol
tem.
will
these
An
amorphous substance
trap volatiles due
solids.
Bowever,
in a
such
freeze-dried
lactose sys-
as freeze-dr-ied malto,se,
to the existence of free volume in
when
exists in a crystalline state.
inositol
is
freeze-dried,
it
The lack of free volume in the
crystalline state limits the ability of inositol to trap vola1
tUes (TO and Flink, 1978c).
The addition of inositol to a
maltose solution decreases the collapse temperature.
Further-
more, the collapse temperature of a maltose-inositol system 15
dependent on the total solute concentration, the solute ratio
in the mixture, and the freezing rate (TO and Flink, 1978b).
Freeze-drying sucrose in the presence of acetone will
cause
~
sucrose to exist in a crystalline state.
of
a
freeze-dried
sucrose-acetone
The humidification
system
showed
loss
of
10
acetone
after
recrystallization
collapse (To and
~'1ink,
1978c).
and
not
To and
as
~'link
a
result
of
H978c) showed
that in a freeze-dried emulsion of glucose and linoleic acid,
the release of entrapped linoleic acid and its s"ubsequent oxidation occurred after the initiation of matrix recrysta1liza-,
tion.
Both of
these experiments
indicated that nei th~r oil
oxidation nor volatile 10ss was occurring after collapse, but
were occurring after recrystallization.
Thus
recrystalliza-
tion would cause enough structural rearrangement wi thin the
freeze-dried matrix to permit diffusion of the volatile to the
exterior and its 10ss by vaporization (To and
~'link,
1978c).
In summary, the abil,ity of substances to retain volatiles
during freeze-drying is dependent on the formation ,of an amorphous solids matrix.
in
freeze-dried
Volatile retention was shown to decrease
substances
recrystallization (To and
c.
which
~link,
undergo
collapse
and
1978c).
Mechanisas for Volatile Retention During i'reeze-Drying
The major portion of
volatile· retained
during freeze-
drying has been explained by the following theories: selective
diffusion and microregion entrapment.
Both the selective dif-
fusion and the microregion entrapment mechanisms describe the
sarne phenomenon but
respectively
from
macroscopic
(King, 1970).
explained by mechanisms which
and molecular levels,
Volatile retention has also been
emp~asize
the adsorption and the
inclusion of the volatile within the freeze-dried matrix (Rey
and Bastien, 1962: Chirife and Karel, 1973.b: Capella!!
1974) •
.!l.,
<
t·
i)
Selecti~e
- 11 -
'D>ffusion Theory
volatile retention occurripg during air drying has been
explained
through the
use of a mathematical
equation which
.
\
describes the flux of an evaporatlng component from the gasliquid
of
interfac~
this
(Thijssen and,Rulkens, 1968).
equation,
Thijssen
and Rulkens
With the help
demonstrated
(1968)
that volatile retention occurring d'uring air drying is dependent primarily on the volatile' s
phase.
diffusivity
in the liquid
In experiments designed to simulate both the 1055 of
water and volatile during drying, diffusion coefficients were
determined
for
acetone
and
water
in mal todextrin solutions
over a range of moisture contents (Menting et
~.,
1970).
The
diffusion coefficient for acetone was about 300 times smaller
than the diffusion coefficient for water.
SU9gest:ed
that
water concentration near
These experiments
the surface can
be
lowered very quickly with'the f1avor retention remaining near
100%.
In freeze-drying, both diffusivity and relative volatility influence volatile retention.
Thijssen (1971) was able to
predict volatile retention during both spray and freeze-drying
through the use of a mathematical model.
This model was based
on the selective diffusion of the volatile with
water.
t,.
The model made provision for
the
respeét
formation of
distinct phases as aqueous solutions were frozen slowly:
and the concentrated amorphous solution (CAS).
>,t
to
two
ice
The composi-
tion of CAS after freezing included: water, dissolved solids
,
.'
12
..
and volatiles.
The concentration of water in the CAS could be
~
determined from the freezing curve of the solution.
, During
ables
freeze-drying,
diffus~h
ta the void
the retreat of
ice front en-.
volati~es
of both water vapor and
a~at
the
from the CAS
the exterior of the solids matrix.
diffusion of both water vapor and
volatiles . was
thought )to
occur via open capillaries in the freeze-dried matrix.
tiles exposed at the
wÇ>uld
!,'
be
and
voia-
between the solids and the void
by vaporization,
~ssèn
studies
i"
lost
interfac~
\ The
Rulken~,
not
1968;
sublimination.
Other
Menting
1970)
et al.,
-
hav'e shown a much greate'r decrease in the diffusion coefficient of acetone as compared to water in
qissolved
~olutions
of inereasing
These studies demonstfat~ that a
soUds content.
~
preferential\loss of water occurred in comparison to volatiles
during freeze-drying.
~'urther
removal of water from the
solids matrix would
continue to oceur as a result of a temperature gradient betwe~n
the
dried
solids and
the
sublimation
water ~ concentration is decreased,
completely
cules.
are
impermeable
to
the
front.
As
the
the solids matrix becomes
transport
of
volatile mole-
The concentration of water at which volatile Molecules
completely
retained
is
known
as
the
critical
water
concentration.
\
'
The selective diffusion model has the flexibility to take
into account the solubility of the volatile found within the
.t,I
CAS (Etzel and King,
19801
Massaldi and King,
, ,.
"
1974a).
When
..
,
- 13 -
..
volatiles are homogeneously dissolvèd in the CAS, retention i8
governed strictly by selective diffusiQn
(Thijssen and
Rul-
/,
1970~
kens, 1968; Menting et a1.,
Massaldi and King, 1974a).
For vola.tiles ini tially present at concentrations above
their solubiÙty" volatile loss was governed by both diffusion
p
and
the location of the volatile droplet
sample (Massaldi and King, 1974a) ,.
in
the CAS
after
freezing
were
within
the
frozen
Volatile droplets embedded
largely
retained7
whereas 1
droplets of volatile located at the interface between the CAS
and the void are lost by vaporization.
The formatjon of distinct droplets "of volatiles during
c
freezing was attributed
During
volàtile
the
is
freez ing
to
of
dep~ndent
a
decrease in
solution,
a
their
.
the
solubility.
solubility
on both low- temperature
and
~
of
a
elevated
concentration of volatile due to the removal of water as ice.
Any movement of" volatile
and
the
void would
dr0~lets
lead
to
to the interface of the CAS
volatile
loss
by
vaporization
(Ma8saldi and King, 1974a) •
..
. In an .ttempt to explain their results, Massaldi and King
(1974a) described
vol~ile
retention. for different concentra-
tions of volatile in terms
Boweve,r,
of
the selective diffusion model.
the authors menti7d the
-their model:
(1)
1
following 1 imi tations
to
for volatiles of low solubili ty such as n-
hexyl acetate, the retention was lower than expected when the
droplet size was greater than the thickness of the amorphous
matrix,
(2 )
a correction was . not made for
8(/
the occurrence of
-.
- 14
1
Brownian diffusion at the CAS accumulation
of
vo~at-ile
Thus,
ice interface.
droplets
-during
freezing
any
would
increase the diffusion of droplets to the interface of t'he CAS
and the
,
\
~y
Volatile present at the interface would be lost
vo~d.
vaporization and the volatile retention would decrease.
Massaldi
and
King
(1974a)
have
also
applied
their
selective diffusion model to the retention of d-limonene in
freeze-dried
commercially frozen
concentrate j uices
(CFCJ).
An important consideration when applying the diffusion model
to
conce~trated
orange juices 15 the formation of a cloud com-
posed of suspended colloidal matter.
~hat
These authors suggested
cloud particles would collect at the interface between
the CAS and the void due to a polarization effect caused by
ice crystal growth.
The formation of such a barder by the
cloud particles would impede migration of volatile oil droplets to the interface between the CAS and the void.
Further-
more, an improved d-limonene retention was shown experimentally by increasing cloud densi ty in the supernatants "of the CFC
.
~
juice centrifuged for 30 min at 13,200 xG (Massaldi and King,
1974c) •
The retention of d-limonene was examin,ed in freeze-dried
solutions' containinq lipid as a secondary phase (Massaldi and
King,
1974b).
The presence of an organic phase such as
a
t~'...lipid, promotes a partition of the d-limonene between both the
aqueous and the orqanic phases of
t~e
solutions.
an increase in the initial concentration of
Furthermore,
d-limon~ne
results
•
-~
/'
.
..
v
in an
increase in
the number of d-limonene droplets
Massaldi and King (1974b)
aqueous
phase.
..
in the
concluded that the
retention of d-limonene initially present in the aqueous phase
was not influenced by the presence of an organic phase.
The effect of an organic phase on volatile retention was
also
examin'ed
by
determining
the
retention
sucrose solutions which contained emulsified
. and King, 1980).
of
acetates
peanu~
in
oil (Etzel
Using a diffusion model ,similar to that of
Hassaldi and King
(1974a), Etzel and King
showed that
(1980)
acetate retention was based on the distribution coefficients
(Kieckbusch and King, 1979) of acetate between various oil and
carbohydrate solutions.
used
to
predict
the
The same type of diffusion model was
retention
of
aldehydes
in
solutions
containing heptanal as the emulsified organic phase.
r
Volatile 10ss which occurred during rehumidification of
freeze-dried
carbohydrate
and
protein
solutions
was
also
explained on the basis of diffusion (Omatete and King 1 1978) '.
Volatile
lasses
incurred
during
high or low moisture contents,
rehumidification
•
systems were rehumidified
content, volatile
collapse •
1055
either
was attributed to changes in
the diffusion coefficient of the volatile.
dried
to
to
When
the freeze-
an intermediate moisture
was shown to be dependent on structural
Changes in web thickness
of the
. freeze-dried systems which were rehumidified.
CAS
occut'red in
To explain the
volatile loss occurring during structural collapse, a diffu-
(t
sion model must account for changes
in ~eb thickness of the
-'
1
.'~
1"'
- 16 -
1
CAS.
In order to explain the loss of volatile occurring dur-
ing structural collapse, a
diffusion model would have tO be
modified to take into account a linear increase in web thickThe observed values for volatile
ness wi th increasin<;J time.
retention
were
in,
agreement
with
those
of
the
modified
'"
diffusion model in systems containing
dextran-10, maltose, and
'" polyvinylpyrrolidine.
In summaryv volatile ~tJ.on in freeze-dried solutions
has
been
successfully
diffusion.
10ss
of
explained
on
the basis of
selective
The diffusion models have predicted a preferential
water
in
systems
containing
either
homogeneously
,
dissolved
...
IL
volatiles
Furthermor~,
or
volatiles
of
limited
solubility.
volatile IQsS occurring as a result of structural
collapse can be predicted by modifying the diffusion model to
take into account a 1 inear
increase in web thickness of the
CAS with time.
ii) Microregion Entrapment Theory
Flink and Karel (1970a) described microregions in freeze,
dried carbohydrate cakes as a complex structure
molecular association
resu~ting
between carbohydrates due
-~
from
hydrogen
)
bonding.
These authors stated that the formati6n of micro-
regions occurred in carbohydrate solutions due to the concentration
process
caused
by
water
crystallization
during
- 17 -
freezing.
regions
As the"moisture content decreases within the microduring
freezing
and
subsequent
drying,
a
complex
structure is produced which affects the permeability of water
volatile
and volat île compounds.'
moisture
content
reaches" a
partiàl pressure
level
was
not
of the
loss
critical
volatile
at
moisture
this
consid'ered sufficient ta
force required for volatile
continues until the
level.
The
critical moisture
{;)roduce
the
driving
Thus volatiles are sealed
1055.
within the microregion of the freeze-dried matrix.
Due to its
small
the
size
matrix,
and
wate~
its
plasticizing
occurs
"
still
1055
action
(r'link
within
Karel,
and
solid
1970a;
Chirife and Kdrel, 1973a).
In an attempt to characterize the microreg ions for:med in
freeze-dried cakes, the size of the microregions wa,s estimated
'1
by determining the amount of volatile beIore and after grinding of the cakes and subsequent vacuum drying of freeze-dried
)
particles
(I.-'link
neither before
and
Kara!,
1970a).
Volatile
nor after grinding which
loss occurred
ind ccated
that
the
mi'croregions were smaller than the average particle size after
grinding.
In further experiments, both the localized nature
of volatile retention in microregions and the relative permea-
.'"
bility of the
demonstrated
freeze-dried
using
cake to water and volatile, were'
freeze-dr led
maltose
cakes.
lni tially,
maltose solutions were prepared with and without propanol and
then
layered
drying,
successi vely
in
a
test
tube.
After
freeze-
the soids matrix ",as freeze-fractured and each layer
-
~he
vas analyzed for propanol.
res~~ts
18 -
indicated that propan-
ol ",as entrapped in microregions of the freeze-dried
eake and
that the permeability of the layers to propanol during-freezedrying was amaller in compariaon to the permeability of water.
Further evidence of volatile entrapment by microreg ions
vas
shown
cakes
by
the
containing
rehumidification of
volatile
(Flink
and
freeze-dried
Karel,
maltose
1972) •
The
freeze-dried cakes were equilibrated by sorption to different
A~
levels of water activity.
in
the
cakes,
occurred
both
within the
water adsorption inereased with-
structural
matrix.
changes
and
volatile
The microregions of
a
loss
freeze-
dried maltose cake contained amaller amounts of volatile after
t
rehumidification to new moistuF,e levels.
The mechanism for
-entrapment of volatiles during freeze-drying by the formation
of mièroregions was extended to model systems containing polymers.
Whcn
freeze-dried
Rarel,
1970a;
Chirife
cakes
and
of polysaccharide
Rarel,
1973a)
and
(FUnk
protein
equilibrated to different levels of water activity,
lution
of
the microregions
é\nd
the
loss
of
associated with different moisture contents.
other
polymerie
systems,
the
and
were
the disso-
volatile
were
In contrast to
polyvinylpyrrolidone
solution,
required longer times to approach lower equilibrium levels of
volatile
( 1973)
concentration wi thin
ti vi ty
Chirife et
al.
suggested that this difference may be ,ei ther due to a
reduced mobility of
\, l
the matrix.
of
polar
the polymer or due to a greater sensibonds
in
polyvinylpyrrolidone
to
'-
disruption of the solids matrix in the presence of water.
the
- 19 -
1
Hexanal droplets were observed by optical microscopy in
particles of a freeze-dried maltodextrin slab (Flink and GejlHansen, 1972;
~
Flink
aL,
1973).
Further observations on
systems containing maltodextrin and other volatiles
indicated
that the formation of droplets and their size were dependent
on the solubility of
the volatile within the
aqueous phase.
When observed by scanning electron microscopy,
the surface of
the freeze-dried mal todcxtrln slabs containing hexanal showed
ci rcular depress ions.
These circular depressions were of a
size similar to those seen with the optical microscope.
Simi-
......
1ar observations were reported by Kayaert (1974) on the interface
of
wt~
a
containin~
dried
gum
containing
no volatiles had smooth
hexanol.
surfaccs~
Samp1es
whereas, samples
which retained hexanol showed bubbles on the surface.
dried samples which lost a greater amount of
visible aftermarks on
that increases
the surface.
in volatile
to. confirm the
freezing and cooling.
hexanol showed
These authors
suggested
retention would correspond to an
increase in the number of bubbles.
stage was used
Freeze-
A freeze-drying microscope
formation of
The droplets were
~~~n
droplets during
to be entrapped
j
after fr'eezing
drying.
eva1uated
and
locked
into 'th,e dry material
by freeze-
The ability of microregions to encapsulate lipids was
in
(Gejl-Hansen
solutions
and
Flink,
of
maltodextrin,
1978).
Greater
avicel
and maltose
amounts
of
l ipid
material, su ch as oil, were encapsulated in maltodextrin solutions as
the
initial
concentrations of oil
:were
increased.
- 20 \
Substances such as
maltose
which
dur ing freeze-drying, showed a greater amount of
la t ion
..
as compared
matrix
form an amorphous
011
encapsu-
to substances which formed a crystall ine
matrix during freeze-drying •
'~
,
:1
In
summary,
volatile
retention during
freeze-drying
has
been expl fllned by the forma tion of microreg ions which en trap
\
The greater perrneabi 1 i ty of water as compared to"
• volat.i1es.
"
volatile,
1
causes
freezing
and·
drying and promote hydrogen bonding between molecules of
the
sol ids matrix.
The mechaniscm for microregion entrapment
has
been
to
extended
solids
to
concentrate
systems
during
containing
different
polymers (eg., proteins .and polysaccharides)
L
types
of
and to volatiles
.of low solubility in a<J'ueous solutions.
ill) Adsorption and Inclusion
Rey and pastien (1962) reported an increase in the amount
Il
of
acetone
retained
during
freeze-drying
Earle' s
when
salt
solutions were supplemented with glycine and various amounts
"'"'"
of glucose.
The increase in acetone retention was thought to
be due to the sorption of acetone on glucose.
The occurrence
of sorption was also demonstrated between low"molecular weight
a1cohols
and
dry
cellulose
(Lauer and
Ayer,
1957;
Columbo,
1969; LeMaguer, 1972).
The
adsorption
'Of
volati les
polymer ic substances such as:
et
.Tt.
....
!!.!.,
1973),
egg
and
was
demonstra ted
polyvinylpyrrolidone
bOlline
serum
alburnin
wi th
(Chirife
(Benson
and
-
21 -
Richardson, 1955) and pepsin (Chirife and Rarel, 1974b).
The
contribution of adsorption
to volatile retention in
dried polyvinylpyrrolidone
solutions is considered
freeze-
important
when s\mPles are frozen r,apidl Y (Chirife et al., 1973).
these Samples were
volatill
retained
microregions.
sorne of
the
frozen
\rias
slowly and
thought
~
Bartholomai
benzaldehyde
al.
retained
be
was
entrapped
w
i thin
the
the
(1975) also indicated that
retained
extract "las due to adsorption.
benzaldehyde
to
then freeze-dried,
When
in
freeze-dried
mushroom
However, the major fra-ction of
considered
to
be
due
to
the
mechanism of microregion entrapment.
Franzen ,md Kinsella
(1974)
have
shown
the
interaction
between the flavoring volatile and the protein to be dependent
upon the type of protein, the type of flavoring volatile,and the
Solms et
presence of endogenous components or cont,aminants.
al.
(1973) have stressed the importance of hydrophobie inter-
action
between protein and
ligand with
retention during processing.
the
protein was se en
denaturation (Arai
~
to
respect
to
volatile
The amount of volatile bound to
increase
aL, 1970).
as
the protein
underwent
Chirife and Rarel
(1974a,b)
reviewed the experimental procedure of ht"ai et al. (1970) and
stated
that
contrary
protein denaturation,
to
as
the
q
conclusion of
these
authors,
retention mechanism, could not be
proved responsible for an increase in volatile retention.
..
heating
of a
protein
solution
in
the
presence
of
The
organic
compounds may increase sorption of volatiles due to mechanisms
1
.~
._... -" ...-..... _----....---
- 22 -
1
other
than
occurrenc~
unfolding of
the
protein
of a chemical reaction.
and
May
increase
the
Chirife and Karel (1974a',
J
bl suggested that the hydrophobie interaction between volatile
..
and protein was overemphasized
retention.
These
microregion
entrapment
as a
authors aga in
of
mechanism
asserted
volatiles
for
the
during
volatile
importance of
freeze-drying.
Damodaran and Kinsella (1980) showed the interact ion between
protein
and different ketones
to be
hydrophobie
in nature.
The binding affinity of carbonyls to bovine serum albumin was
influenced by chain
len,~th,
functional groups, and the struc-
tural state of the protein molecule.
For example, the
stru~­
tural state- of bovine serum albumin was modified by reducing
..
the number of disulfide bridges.
The change in structural
state of the protein caused the binding behavlor of 2-nonanone
to increase.
~~
The
interaction between
flavor
molecules
and
carbohy-
drates can a1so take the form of inclusion cpmplexes,for exampIe, starch or amylose with an organic molecule
(Be,ar,
1944; Mikus et al., 1946; Rundle et al., 1944).
1942;
The formation
of starch inclusion complexes in systems similar to foods was
shown to require a temperature gradient which favored struc-
1973) •
.
compounds and
tural rearrangement of starch molecules (801ms et al.,
Osman-lsmail and 50lms (1972) compiled a list of
temperatures
starch.
at which
Through
inclusion
complexes
werè
the use of Scatchard plots,
formed
two di fferent
1
~
_.--_._- -------..
~-~~#.-
--- . _-----_..
~
with
_--~
....
- 23 -
types of binding sites were identified:
( 1) si tes where in-
clusion complexes can form withln the ïnterior of the starch
helix,
of
the
(2) sites where interaction can occur with the surface
heHx
(Osman-Ismail
•
and
Solms,
1972;
Solm et
.!l.,
1973).
.
In sununary, the microregion entrapment and the selective
.
diffusion mechanisms explain volatile retention during freeze-
.
drying either through the entrapment of volatile by the interaction 'of solids by hydrogen bonding or through differences in
diffusion rates between the volatile and water.
iam emphasizes
the
J
importance of the
formation of two separated phases.
content
was
cqnsidered
to
be
Bach mechan-
freezing step for
the
The influence of moisture
critical
in
determining
the
extent of vol~tde retention and the structure of the solids
~)
in the freeze-dried matrix.
Bach of these mechanisms is able
to account for the major portion of volatile reta..ined during
freeze-drying.
Adsorption
and
inclusion
were
considered
-
secondary mechanisms when explaining volatile retention during
freeze-drying.
The contribution of
adsorption
to volatile
retention was shown to be dependent on the freezing rate, type
of
dissolved
solids,
the
presence
of
moisture,
presence of endogenous eomponents or contaminants.
and
the
Adsorption
of . volatiles to t>roteins has been shown. to be due to hydrophobie
sueh
.
,(
\-
as
interaction,
volatiles,
whereas,
can
çarbohydrate Molecules.
be
other
included
small
organic
within
the
MOlecules
helices
of
- 24 -
1
D. The Effect of Processing Paraaeters on Volatile Retention
During Vreeze-Drying
King
(1971)
app1ied
Thijssen's
diffusion
concept
to
predict the qualitative effects of processing parameters upon
volatile
volat ile
retention
during
freeze-drying.
retent ion were pred icted by a
Increases
in
dimensionless number,
derived from pourier's equation,
OtL -2.
(3)
This dimensionless number was def ined
in terms of
tile's diffusivity within
matrix
the solids
the vola-
(0),
the
time
during which diffusion can occur dUriDg freeze-drying (t), and
the size or thickness of the region from
1
wh~ch
volatile
1055
,
occurred
(L).
The volatile retention
in model solutions and
food 1iquids was predicted to increase during freeze-drying by
reducing th~ value of the dimensionless number.
~'link_
and Karal (l970b) explained the effec;ts of process-
lng condi ti,ons on volatile retention during freeze-drying
terms .of
the formation of
the microreg ion.
in
Each process i ng
parameter affected microregion formation and consequerrtly the
volatile' s 'permeability through the solids matrix during drying.
Volat He 10ss was seen to be dependen t
on the rate of
drying 1 the type of solids and the local moisture content of
t-he solids matrix.
~'link (1975) considered the most
important
processing parameters during the freeze-drying of model solutions to
be the following:
iee
front
temperature,
freezing'
"
t
rate,
and
sol Ids coneentrat ion.
\
The
processing
parameters
•
'.,
- 2S -
which
affect
volatile
retention
during
freeze-dryinq
are
discussed below:
'i) Freezing Rate
An
improvement
freeze-dried
model
in volatile
retention W;as shown in both
solutions and
liquid foods
slowly
in still air (Thi.jssen and Rulkens,
Kare!,
t 97.0b:
Flink and Labuza,
1972;
by
1968;
voilley
~
freezing
Flink
ànd
al., 1973;
.,Chirife and Kare!, 1973a; 1973b; 1974b; Kayaert et aL, 1975;
Smyrl,
,
1977; Gero and Smyrl, 1982).
The. effecir of reducing
"
, '.
€:hé freezinq rate caused freeze-dried samples to form fewer,
but larger microreqions with a greater concentration of solids
(Flink and Karel, 1910b).
These microregions wquld show lower
permeability' to volatiles as compared to water during drying
and consequently lead to an improved volatile retention.
King
(1971)· indicated that slow freezing forms larger iee crystals
an~
hence causes
the Bolids to
form
thieker microregions.
These areas of coneentrate would lead to increased volatile
retention due to the increase in the size and the thicknêss of
the microreqion.
In contrast,
formation of
small
small,
many
rapid
iee crystals
thinner mieroregions.
freezing leads to
and ; consequently.
Many
.
The microregions formed during
fast-freezing have a lower concentration of soHds in
ison to those formed during slow freezing
1 ~70b) •
\~
l
"
the
comp~r­
(Flink and Karel,
The lower soUds concentration leads to a~ increase
in the permeability of the Boliels matrix to volatile movement
•
..-.,",~
............ -
......
,
•
, .......... _ _
1
_"
••
- 26 -
'
1
and will a1so cause a decrease in volatile retention.
Studies
~
conducted
on
tomato
juice
{Gerschenson
raspberry juice and orange juice (Sauvageot
et
1979) ,
al.,
~ ~.,
1969) also
'confirmed that a decrease in the freezing rate (slow freezing)
improved volatile retention as compared to fast freezingo
ii) S!!ple Diaerisions
Volatil:e retenti on during freeze-dryin<j c)s dependent on
swnple thickness
for both model solutions and
1968~
(Thijssen and Rulkens,
Karel~
1970b:
Flink
and
liquid foods
Sauva<jeot et al., 1969i Flink and
Labuza,
1972;
Chirife
and
1973a; 1973b; Chirife and Karel, 1974b; Smyrl, 1971)
t.
freeze-drying,
Karel;
During
0
th!n samples are exposed to a steep moisture
'~
gradient at the
sublimation front
interval
which
during
the
0
moisture
AS
a result,
content
the time
of the
solids
remains at moisture levels great enough to permit permeability
of
the volatile
through
microregions,
decreases
and
hence
leads to an increase in volatile retention (Flink and Karel,
1970b).
King (1971) stated that increases in volatile reten-
tion with
dècreasing
sample thlckness were the result of a
1
fi,igher velocity of the advancing sublimation front.
Higher '
velocities of the sublimation front decrease the time (t) during which diffusion of the volatile occurs and consequently
leads to an increase in volatile retention.
was used by Sauvageot
of
natural
volatiles
•
~
al.
in
This explanation
(1969) to explain the retention
raspbérry
juice '.which
decreased
o
-
1
27 -
slightly as sample thickness W8S increased (Sauvageot et al.,
1969~. '.
Howeve[)n contrast to these results, both Gerschen-
son et al.
volatile
(1979) and Flink (1975) have reported increases in
retention
freeze-dried
with
tomato
Flink (1975)
juice...
increases
juice
and
in
sample
thickness
freeze-dried
sU9gested that in
for
canned
tomato
the case of
freeze-
"
dried
canned
free~ing
tomato
j uice,
thicker
layers df
sample
cause
to occur at a slower rate and thus improve volatile
retention.
Smyrl
reported
(1977)
'.
that changes
in surface area had
little influence on carvone retention in either sucrase or 9um
arabic solut,ion.
Sample thickness wa'S kept constant through-
out the experiments.
iii). DEYinq Rate
The rate of freeze-drying was shown to be dependent on
the temperature of the frozen zone in the drying sample.
Dur-
ing freeze-drying this temperature can be controlled by modifying
1
-
the chamber pressure and the temperature of
source (Bellows and Kin9,
thrqu9h a
could
be
1972).
mathematical model
achieved
by
the heat
Thijssen (1971) predicted
that higt\*er volatile
freeze-drying
·pressures which doubled the drying rate.
samples
Por
retention
at 0 chamber
the se samples,
the retention of propanol was increased (Rulkens and Thijssen,
1972) •
Several authors have reported. a decrease in volatile
retention
... ..,
~
...... ",---_.... - -
.-.-
as
._-~-_
the
. ..
~-
iee
front
temperature
was
~--- ~~-
\
increased
,
(
28
(Thijssen, 1971: Voilley
~
al.,
An increase in the
1973).
ice front temperature causes aO decrease in
CAS.
-
viscosity of the
This decrease in viscosity promotes structural collapse
during
freeze-drying
and
therefore
leads
to
a
decrease
in
volatile retention.
During
freeze-drying,
heat
may
be
either
transferred
through the dry layer or through the frozen layer of the drying sapPle.
The transfer of heat through either the dry layer
or through the frozen layer in model solutions,held at a constant ice front temperature, produced no di f ference in volatile retention.
A decrease in ice front
temp~rature
reducing the amount of heat input resulted
volatile loss.
in an
caused by
increase of
If both dextran and glucose samples are heated
over the sarne range of platen temperatlJres (70-150 o!-,), .. glucose
samples
show
a greater amount
•
of structural collapse.
The
(1
occurrence of
structural
collapse wi thin
the
would eliminate the beneficial effect of an
rate,
and
consequently
collapse vas
1
averted in
increase
volatile
sol ids matrix
increased drying
loss.
the solids matrix
by
However,
using dextran
samples. Volatile retention inereased in the dextran samples ",hen
heated
wi th
the sarne platen
tempera tures
(l"link.
and lCarel,
1970b) •
S imilar experiments were used to show the effect of iee
front
.
Whon
ternperature
chamb~r
vacuum),
on volatile
pressures
volatile
were
retention was
retention
in
increased
(i.e.
d~creased
coffee extract.
decrease
1
..
in
in coffee extract
~
•
'.~
1
•
- 29 -
due
to structural
(Ettrup-petersen
et
promoted at high
requirements for
collapse
al.,
within
the
Structural
1973) .
chamber pressures as
~he
freeze-dried
matrix
collapse
was
smal~ler
a resul t of
transfer of sublimation heat.
King (1971) also considered the influence of the sublimation front temperature on volatile
drying.
retention during
freeze-
volatile retention was shown to increase if the tiae
interval for volatile diffusion Ioii th in the .01 ids aatrix 18
red'lced -
Time
increasing the
intervals for diffusion could be reduced by
velo~ity
of the sublimation front.
An increase
in the velocity was achieved by increasing the temperature of
the
sublimation
front.
In
contrast,
a
decrease
in
the
subI imation front temperature would be expected to increase
the
concentration of
the
soUds
in the
microregion.
J
An
increase in the concentration of the solids was predicted to
increase volatile retention by lowering the diffusivity of the
volatile.
Experimental
results
were
presented
by
both
Sauvageot !! al. (1969) and Flink and Karel (1970a) to support
this effect of the sublimation front temperature on volatile
retention during freeze-drying.
Iv) Solids Ca.position
The retention of volatiles during freeze-drying has been
studied
(Thijssen
with
respect
and
Ruikens,
.
to
different
1968;
types
Saravacos
Sauvélgeot et al., 1969; Flink and Karel,
Karel, 1973a,b;
of
and
carbohydrate
Moyer,
1968;
1970b; Chirife and
Kayaert, 1974; Smyrl, 1977; Gero and Smyrl,
- 30 -
1
1982).
When freeze-dried urider ident ical condi tions •
accharide
solutions
in comparison to
ahowed
ei ther
a
415-
greater
volatile retention
monosaccharide
or polysaccharide
conditions (Flink and Karel, 1970b).
The type of disaccharide
used to prepare the model solutions was also found to influ-
•
ence volatile retention.
Sucrose
solutions
showed greater
volatile retention than maltose and lactose solutions during
"
1
"t
o~
freeze-drying when prepared
f
.
"
and
Karel,
1970b).
an equal weight basis
A comparison of propanol
polysaccharide sOlut+ons
indicated
that
(FUnk
retention
in
cellulose decreased
volatile retention to a greater degree than starcn or dextran
l
solutions
Chirife
(Flink
and
1970b~
and Karel,
Karel
(1974b)
have
other types of polymers, such as
Chirifk
investigated
polypeptide~
volatile retention during freeze-drying.
'vinylpyrrolidone,
a
et
water soluble
al.,
the
1973).
effect of
and proteins, on
Solutions of poly-
polymer
containing
polar
groups similar to proteins, showed lower retention'of s?luble
compounds as compared to dextran and maltose solutions.
mentioned
above,
differences
observed with different
t~pes
in
volatile
of proteins.
retention
As
were
Chirife and Karel
,
(1974b) reported a higher retention of 2-propanol in a pepsin
solution as compared- teS that found in a bovine albumin solution.
Heat denaturation of the protein did not si9nificantly
influence volatile retention.
The
...
influence of gelation on volatile retention during
freeze-drying has been' examined by severai authors (Saravacos
~
-
- . J'
11#" •
.Jo
~
. ----'""'- .... - ....
•
- 31 -
J
and Moyer" 1968, Kayaert,
Kayaert e't al., 1975').'
1974;
addition of glucose to a pectin (low methoxy) gel
acetic
,',
acid
retention
Moyer, 1968).
during
freeze-drying
Similar increases
The
increased
(Saravocos
in volatile
and
retention were
~.-'
observed when sucrose was added ta a gel mixture containing
-
35% locust bean gum, 20% guar gurn, 15% carageenan gum and 30\
guar gum
(Kayaert
al.,
~
Kayaert
1975) •
et
al.
( 1975)
attributed the retention of' organic volatiles within the gel
mixture
O
to
microregion
entrapment,
with
li ttle contribution to total volatile
adsorption
retention.
having
Etzel and
King (1980) used the selective diffusion mechanism to
pre~ict
volatile retention in a model.food gel for both homogeneously
i
dissolved
volatiles
and volatiles of
limited
solubility
in
aqueous solutions.
Ofcarcik and Burns (11974) studied the influence of binary
carbohydrates
Model
mixtures
solutions
th~
on
containing
retention
binary
of
mixtures
pyruvic
of
acid.
lactose
and
glucose showed a synergistic effect by increasing the retention of pyruvic acid v as compared ta individual solutions of
lactose and glucose.
No
increase in pyruvic acid retention
was observed when freeze-dried mixtures of sucrase-lactose and
sucrose-g~ucose
were
compared
glucose,
sucrose' and
lactose.
mixtures
when
ta
significant
added
increase
ta
None
Bermuda
in
indiyidual
of
these
anion
juice
carbonyl
solutions
of
carbohydrate
'caused
retention
any
during
freeze-drying.
...... ~.,--
.. --_. ...
(
------
- 32 -
,Seve.a~
•
investigators
1977; Smyrl and LeMaguer,
(Flin~
1978)
and
Karel,
1974b;
have studied
Smyrl,
the effeet of
adjusting the pH of freeze-dried solutions eontaining proteins
and earbohydrates.
increased
Smyrl (1977) showed that carvone retention
at h igher
and lower pH val ues, wh He the
lowest
retention oceurre'd at neutral pH values in both sucrase and
glucose solutions.
Gum arabie solutions eontaining the vola-
\ ,
tiles eugenol and earvone
were
shown
to lose
amount of volatiïe at a pH value of 5.0.
that
incr€~~~s
the
greatest
The author suggested
in aeidity enhance hydrogen bonding interaction
thus promoting a large number of
between dissolved solids,
microregions.
•
v) Solids Concentration
Increases in volatile retention during freeze-drying have
.
been aehieved by increasing the initial concentration of dissolved solids
(Rey and Bastien,
1962:
Saravacos and Moyer,
1970b~
1'968: Sauvageot et al., 1969; Flink and Karel,
and Karel, 1973a;
Thijssen
(1972)
1974b~
Kayaert et al., 1975).
improved
volatile
retention
Chirife
Rulkens and
through
the
addition of dissolved solids, up to a critical value of solute
concentration above which further increases in retention were
A cri tical mal tOdextrin concentration of 20 wt%
not found.
was
.>
found
drying.
t
solutions
glucose,
to
optirnize
volatile
retention
during
freeze-
A maximum level of volatile retention was shown in
of
maltose
gum arabic
(Sugisawa
(Smyrl,
j
1971),
et
al.,
1973),
sucrose,
dextran (Gero and Smyrl,
•
1
1982), and binary combinations of carbohydrates (Ofcarcik and
King (1971)
Burns, 1974).
grea~er
interpreted
the effect of ad'ding
amounts of dissolved solids in terms of an increase in
the size and thickness (L) of the microregion.\ Such an effect
is
"
-'l
predicted
by
Fourier's
equation
to
increase
volatile
retention.
Flink and Karel (1970b)
.a
demonstrated experimentally that
definite value for glucose concentration could be establish-
ed as being" most efficient when considering acetone retention
per unit weight sugar.
concentration
propanol
were
system
Similar results for an optimal solids
also
(Chirife
found
in
et
al.,
Cl
pOlyvinylpyrrolidone-n1973)
and
in
different
propanol-protein systems (Chirife and Karel, 1974b).
vi) Initial Volatile concentration
Several authors (Flink and Karel, 1970b; Chirife et al.,
1973; Chirife and Karel,
:
1973a;
1974b;
Bartholomai et al.,
1975) have reported a decrease in volatile retention wi th an
increase
in
and Kare!
tration
fraction
ini tial volatile
(1970b)
was
of
However,
Flink
showed that as the initial volatile·concen-
decreased,
the
concentra t,ion •
volatile
initial
retention,
concentration,
maxim~m retention was achieved.
expressed
increased
as
a
until
a
This behaviour was explained
by either or both of the following phenomena: (1) for concentrations of volatile above its solubility limit at freezing, a
lower fraction of volatile retained was found resu!ting from
- 34 -
J
(2) as the initial volatile concentratÙ>n
droplet formation,
increased,
the
plasticizing effect of
concentrated solids rnatrix affected the
the
volatile
d~ffusion
in
the
coefficient
of the volatile and cOQsequently lead to a decrease in volatile
retention
studied
(Massaldi
and
King,
Srnyrl
1974a).
(1977)
the effect of initial volatile concentration on
the
1
t
retention of sparingly 31uble cornpounds in sucrose and gum
arabic
solutions.
,
.plotted
as a
The percent retention of the volatiles was
function of
the ratio of the
initial volatile
concentration to the volatile solubility a.t 10°C.
sparingly soluble
volatiles
AIl of
the
a 'decrease in retention
showed
with increasing values of this ratio.
Flink (1975)
state~
that between the concentration range
of 1000 ppm to 1.0% (wt/wt), the fraction of volatile retained
during
ini~ial
an
freeze-drying was
for
volatile concentrations between 100-1000 pprn (wt/wt),
increase
in
volatile
observed in solutions of
1972)
However,
relatively constant.
sucrose,
glucose
Froscher,
(Voilley
1969),
gurn
et
retention during
dextran~
mixtures
al.,
tomate
juice
,
was
maltose (Flink and Labuza,
with
1973),
freeze-drying
sucrose
orange
(FUnk,
(Kayaert,
juice
1975)
and
(Berry
1974)
and
clarified
tomato juice (Gershenson et al., 1979).
vii) Type of volatile
King (1971) has indicated that diffusivities for different trace organic volatiles in solution \<Iould have the same
- 3S -
order of magnitude.
As
~
result most volatile compounds show
the Barne retention during freeze-drying even though they may
differ with respect to relative volatility.
Flink and Karel
(1970b) have stated that volatile retention was independent of
•
vapor pressure.
Furthermore, volatile retention could not be
correlated with volatility for compounds differing in vapor
"
pressure and molecular size.
Massaldi and King (1974a) have a1so considered the effect
"
of the solubility of a volatile on retention.
Sharp decreases
ln retention \-lere shown for volatiles below their solubility
limit;
whereas,
volatile retention approached a maximum for
concentrations above the solubility limit.
In
summary,
volatile
losses
may
be
prevented
during
freeze-drying if the following conditions are maintained:
(1)
hi9h initial dissolved Bolids content, (2) low freezing rate,
(3)
10\'1
ice front temperature, ( .. ) high drying rote,
initial volatile concentration,
for the
1
volatiles
and
. (7)
(6)
high
(5)
low
991ubllity 11mit
th!n layer of ...pIe.
- 36 -
.1
III.
A.
MATERIALS AND IIIrrRODS
Chemicals
AlI model solutions were prepared with the fOllow~w
molecular weight fatty acids:
acetie acid
(\~),
pionie acid (Anachemia), n-butyric aeid (Aldrich),
pro-
~sovaleric
,
acid (Aldrich), and valerie acid (Anachemia).
AlI acids were
used as reeeived without further purification.
Four different
,types of water soluble hydrocolloids were used as dissolved
solids
in
Anachemia),
the model
granular
solutions:
gelatin
citrus pectin (lab .grade,
(lab
grade,
arable powder (lab grade, Anaehemia)
.1
Anaehemia),
gum
and corn syrup solids
(amaizo powdered FRO-DEX 24, D.E., 20; American Haize products
Company, Harmond, Indiana, U.S.A.).
The reported composition
Each model
of the corn syrup solids is given in Table 1.
solution was prepared with solutes and glass distilled water
=
on a weight ~~ weight (wt/wt) basis.
In experiments requiring the addition of low molecular
weight solids " the following
compounds were used:
sucrose
(anhydrous, reagent grade, AldriCh), D-(+)-glucose (anhydrous,
reagent grade,
Aldrich),
glycine
(Baker
grade 1
Anaehemia),
calcium chloride (reagent grade, Anachemia), potassium hydrogen phthalate (reagent grade, Anachemia), and sodium chloride
(lab
grade,
Anachemia).
One
normal
solutions of
sodium
hydroxide (reagent grade, Fisher Scientific) and hydrochloric
acid (reagent grade, Allied
~hemicals)
were used to adjust the
pH of solutions of gelatin, pect!n and corn syrup solids. '
'-_ ...
- 37 -
Table 1.
Corn Syrup Solids Compositionl
,
1
.'
~,
6.0 .
Moisture content (t)
L
~,
r
Dextrose equivalent
28.0
\
S02
(ppm)
40.0
pH of a 50% wt solution
4.5
, dry basis
Carbohydrate composition
((
monosaccharides
9
disaccharides
8
trisaccharides
8
tetrasaccharides
8
pentasaccharides and higher
1
67
American Haize products Company, Harmond,
J
U.S.A.
.\ .i-
..
Indiana,
,.
- '38 -
B.
lquipaent
1•
Freeze-Dryer
)
1.
'.'
AlI
model
Freeze-Dry 5
solutions
were
freeze-dried
in
a
Labconco
eguipped with a Vac Torr- vacuum pump.
The
vacuum pump was belt driven with a capacity of 75 L min- 1 and
ul~imate
an
vacuum of 0.1».
The freeze-dryer was fitted with
a· 16-port drying chamber (33 cm diameter x 33 cm height) which
.
~
held a drying tray containing three' shelve~.
T
was cooled to -54·C by a
,,'
fre~n
an iee holding capacity of 5
The condensor
refrigeration system, and had
L.
The chamber pressure was
measured with- . McLeod pressure gauge hav1ng a range of ~mm to
S)I of mercury (8g).
2.
Gas Liquid Cbroaatograpb
Patty acid solutions were analyzeq using a varian model
3700 chromatograph eguipped vith dual flame-ionization detectors.
The separation of fatty acids was achieved in a glass
column
(183
coated
on Chromasorb W (Chromatographie Speeialties).
cm x 0.2 cm)
packed vith Fluorad e + 10% B3P04
following temperatures and flow rates were used:
port temperature,
temperature,
,
column temperature,
injection
BO·C:, detector
220·C; 30 mL-min- 1 Be (prepurified, Linde Co.);
30 mL min- 1 82 (prepurified, Linde Co.) and 60 mL min- 1 air
• J'
•
(prepurified, Linde Co.).
..
The glass column was fitted vith a
glass precolumn (9.8 cm x 0.2 cm) using a bored through brass
____ ___ --.....-_-.. _
~
l80·Cf
The
'1-------.~--.----
;--"~
. ..--..
~-
--~
- 39 -
1.
'-
'-
-',
union and brass Swagelog fittings.'
that
en~ured
the
stationary phase of
by
charred
"
contaminated
injection.
the
The use of a precolumn
the
column
formed
solids
was
during
not
sarnple
When charring of the dissolved solids occurred in
precolumn,
the
packing material
in
the,$precolumn was
replaced with the sarne packing material present in the column
during analysis.
A Varian
s~rip
chart recorder was used with
a full scale deflection of 1.0 mv and a chart speed of 1.0 cm
min-l.
The variation in the response of the detector was
corrected by the use of the internaI" standard, benzaldehyde
(lab grade, Anachemia).
To further reduce the experimental
error caused by changes in detector 1 s
response, bath sample
and refer~solutions were analyzed successively.
3.
~-
pB lIeter
Corning e Model 5 pH
pB 'measurements were made with a
meter.
The pH meter was cal ibrated wi th the fOllowing stanr
•
dard buffer solutions: pB 7.0 (Corning), pH 5.0 (Anachemia)
and pH 3.0 (Anachemia) •
..
...
Scanning Blectron lIicroscopy
AlI
samples
were
freeze-dried
and
then
fractured
manually breaking the solid matrices into two pieces.
resulting
surfaces
from
these
fractures
aluminum stubs with silver conducting
samples
were
thinly
coated
with
gold
were
by
The
mounted
paint.
The
and
examined
on
mounted
in
a
•
. l
,
1
_~
- 40 -
"
.
Cambridge RStereoscan 600· scanning electron microscope usinq
an accelerating potential of 7.5 kV.
5.
.
.
'
.'
Infra-red (IR) Analysis
Pectin solutions and solute combinat ions of pectin with
eit~er
sucrose, glycine or phthalate
wer~
examined in a Spec-
troprocessor IV spectrophotometer (S,hields Instruments Ltd. f.
Both the cOllstruction and the
op~ation
mater are described by Mills (1963).
ul
of the spectrophoto-
The construction of the
spectrophotometer was modified to permit the analysis of aqueous solutions by eliminating the absorption of water in
reqion.
Special features in the
include the following:
(1)
~he
IR
instrument r S construction
..
the use of a Nerst filament to
- ......... _ J "
.provide a high energy source,
(2) the removal ,of water vapor fro.
,
,
lnterior of the machine by the use of molecular sleves con'"', '
..... '
taining desiccant and by hermetically seali:ng the instrument,
.f
(3)
the
maintenance of
a
constant temperature within
the
interior of the instrument by solid state heaters, and (4) the
use of flow through cells with windows made of barium fluoride
which have hi9h' transmission c~t offs at approximately 12.5)J.
/\1
In addition, the absorption of .water in the IR region was
eliminated by
a calibration program which
was
created
to
obtain a constant energy level by opening and c10s1n9 slits
automatically as the grating moves to a new position.
The
calibration prGgram was run in tandem with a scan of material
1
dissolved in water •
.
41
S!!ple Preparation
Stock solutions of pectin, gelatin'and corn syrup solids
were
prepared
water.
,
"
~
br
dissolving
the
sol ids
Precautions were taken to
avo~
in
glass
distilled
caking of the splids
by ini t1ally heating (60· C) the ...,ater and then dissolving the
soHds with
eontinuous stirring by using a magnetie stirrer
(Corning Co.).
tions,
and
the solids ...,ere added to glass distilled water (23·C)
stir~ed
each
For the preparation of gum arabic stock solu-
stock
(%wt/wt) •
manually.
The amount of dissolved solids used in
solution- was recorded on a weight percent basis
Volatile compounds
freéze-dried included:
and valerie aèids.
added
to the
solutions
to be
aeetie, propionic, butyrie, isovalerie
To ensure that no volatile 105s oecurred
during storage to the atmosphere, aIl Erlenmeyer flasks wère
sealed by a
rubber stopper wrapped with aluminum foil.
The
foU wrap was used to eliminate possible interaction between
the volatile and the rubber stopper.
Samples
)
were
prepared
.
volatile retention,
tile on volatile
,
\
to
--
their
use
in
the
( i) e f fect of sol ids compos i tion on
following. expenments:
volatile retention,
according
(li)
effect of pH and
(Hi) effect of
ionie strength on
type and amount of vola-
retention,. (iv) effect of calcium ehloride
and rate of freezing on volatile ret~ntiori:'
(i) Effect of sol id s'' composition on volatile retention
A 10 mL portion from each stock solution (1% wt/wt) of
hydroco~loids
(pectin r
gelatin,
corn
syrup
solids and
gum
•
- 42 -
1
arabic)
vas pipetted
into tared
Erlenmeyer
inj~ted
Each of the fatty acids was
flasks
-(50
mL).
into this solution usin9
a 10,.uL Hardltou syringe to obtain a final volatile concentration of 600 ppm (vol/vol).
These flasks were then stoppered
,
and s,haken to
hydrocolloid
ensure compl'ete mixing
Finally,
solution.
of the acids and
each
solute
•
,<1
the
(9lucose,
sucrose, glycine, and phthalate) vas mixed vith the different
hydrocolloid -
fatty acid solution to fom a binary combina-
tion with a total solids concentration of 3% (wt/wt).
the flasks were stoppered and shaken
to ensure that solute
.
dissolved completely in the fatty.acid solution.
\..."
of 5 mL from each fatty
acid
Again,
An aliquot
solution containing a binary com-
bination of solid'S acted as a reference for the freeze-dried
sMples.
Both sample and reference were frozen slowly in a
still air freezer at -20·C for at least 12 h.
Samples were
then ready for freeze-drying.
(il> Effect of pH and ionic strength on volatile retention
pOrtions
wt),
. '~
\li (100 g) of pectin (n wt/wt),
and corn syrup solids (5'
"
wt/wt)
gelatin (J% wtl
stock solutions, were
1
weighed into tare'd" Erlenmeye'r flasks (250 mL)
A concentration
of 600 ppm (vol/vol) for each volatile was obtained by injec~
ting 60
L of each acid into the different stock solutions
using a 100)JL Hamilton syringe.
shaken
t '
Each flask was stoppered and
to ensure complete mixing.
buffered
with
2.0
9 of
potassium
The solutions were
hydrogen
phthalate
then
and
43 ''''
adjusted to pH values of 3.0, 4.0, 5.0 or 6.0 with either Bel
or NaOH
( 1 • 0 N)
final weight of
( 1 .0
AlI solutions were
N).
125 9
adjusted to a
with glass disti11ed water.
portions
('0 mL) of the pH adj usted solutions were pipetted into Erlen-
rneyer flasks (50 mL).
The
ionie strength was
increased for
each solution by adding different amounts of NaCl (0.05, 0.10,
0.15
To
g).
prevent
stoppered
immedia~ely
of
fatty
.mL
each
volatile
10ss,
sample
after eaeh procedure.
acid
solution
aeted
were
An aliquot of 5
as a
determining the percent retention after
flasks
reference
freeze-drying.
for
Both
sample and reference were frozen as described previously.
(iii)
EfCeet of
type
and
amount
of
volatile
:;::::::;
on
volatile
,
retention
The effect of changes in type and amount of volatile on
volatile retention was studied in bath freeze-dr ied corn ~yrup
solids and pectin solutions.
syrup solids (5% wj:/wt)
'"~nd
portions
(10 mL)
of
pectin (3.' wt/wt) stock solutions
were pipetted into tared Erlenmeyer flasks (50 mL).
, tdltion range between 50 to 1500 ppm (vol/vol)
,tile 'lias achieved by
acid
into
syringe.
each
These
stock
the corn
A concen-
for eaeh vola-
injeeting appropriate volumes of fatty
solution vi th a 10
flasks
were
~hen
or
stoppered
ensure complete mixing of aeids and solution.
~S
)J
L Bamil ton
and shaken
to
A referenee ior
each ,freeze-dried sample was obtained by pipetting an aliquot
(5 mL) from this fatty acid solution into a tared Erlenmeyer
"
.
'.
"
..
,
flask' (50
mL).
80th
sample
and
reference
-
44 -
solu tions
were
frozen as described previously.
Effect'\ of
(iv)
( CaC1 2)
calcium chloride
and
the rate of
D
freezin2 on volatile retention
Portions of pectin
(3% wt/wt) ,
gel,atin (3% wt/wt) , and
corn syrup solids (S% wt/wt) stook ~olutions were weighed into
tared Erlenmeyer flasks (500 mL).
A concentration of 600 ppm
~\
, ' ~xol/vol) for each volatile was obtained by injecting 120)J L
"
'
of each fatty acid into different stock solutions using a 1.0
These
mL Hamil ton syringe.
flasks j.were
shaken" to ensure complete mixing.
then stoppered and
Various amounts of a CaC12
solution (6.02 9-(100 mL)-l) .were pipetted
into each
fatty
acid solution to obtain five different calcium chloride concentrations (12.4, 24~8, 37.2,62.0 mg mL- 1 ).
mL)
of
each
CaC12-fatty acid
Erlenmeyer flasks
(50
mL).
solution
An aliquot
were
Portions (10
pipetted
lnto
of 5 mL from each
CaCl2-fatty acid solution was used as a reference in determinlng volatile retention.
The procedure was done in duplicate
,\n order ta freeze both the sample and i ts appropriate reference either s10wly or rapidly.
were
frozen
s10wly
when
Samples and their references
t:hey were
freezer at -20·C for at least 12 h.
ready ta be
fr~eze-dried.
frozen
in
a
still
air
The samples were then
The rapidly frozen samples, and the
references were frozen by immersion in 1 iquid
air
(-196· C) •
The rapidly frozen samples were then freeze-dried immediately
after immersion in liquid air, while the references were held
in a still air freezer at
-~O·C
until analysis.
"~
- 45 -
1
Freeze Drying of Sallples
D.
While
in
the still air freezer,
the stopper
from each
Erlenmeyer flask was removed and then the flasks immediately
transferred
to
the
freeze-dryer.
AlI
dried under the fOllowing conditions:
~
charnber pressure of
3 • C,
drying,
moisture
10p Hg for
samples were freezeRopm temperature 23 :1:
24
the Erlenmeyer flasks were weighed
loss
from
the sample.
stoppered and then stored
~t
AlI
After freeze-
h.
to determine
Erlenrneyer flasks
the
were
-20·C for not longer than 2 weeks
before analysis of the sample and its reference.
E.
,.1
Fatty Acid Analysis
The freeze-dried samples were rehydrated wi th glass dis-
tilled water to their original weights.
The frozen reference
solutions were thawed at room temperature (23 ± 3·C).
of
Hl
(4N),
were' pipetted
tions.
containing
the
internaI
standard,
into both the sample and the
Two mL
benzaldehyde
reference solu-
Hydrochloric acid was added to ensure that
the vola-
tile acids vere present in the protonated, volatile forme
The
solutions vere stirred using a magnetic stirrer for at least
15
min
matrix.
in
order
to
completely
dissolve
the
freeze-dried
Aliquots (0.5 PL) of both the sample and the refer-
ence solutions were injected onto the column of a gas-liquid
chromatograph to determine
the amount of each acid
present.
The quantity of each acid retained was represented by a peak
on the chromatogram.
The ares of each peak was estimated by
•
.- 46 -
••
measuring the peak height ,(mm).
The percent retention of each
volatile fatty acid (VFA) was determined as follows:
r
peak height of VFA in sample
, VFA retention :
Differences
in
peak he fiht of VFA in reference
peak heig t of internal standard
phy~ical
properties (solubil i ty, dissociation
constant, boiling point) for
Il
homologous series of volatile
fatty acids can be related t'o ap increase in carbon number of
fatty acids.
An index for volatile retention was
to reflect the retention of aIl
solution
This
1
\' .
by
index
effects
of
solution.
considering
for
The
the retention
volatile
solubility
the volatile
fatty acids in
of each
fat ty
acid.
retention would also consider
and
index was
establis~ed
dissociation
for
represented by the
each
the
acid
in
average of
the
retentions for volatile fatty acids in solution and determined
as follows:
(
1
-1
Average
Retention
of VFA
% Re~.+
= Acetlc
% ~et •. + % Ret.
+
% Ret.
+ % Ret.
ProplonnlC Butyric
Isovaleric
V~leric
5
1
P.
Statistical Analysis
The
obtained
reported
retention
from
wi th
at
values
least
their
were
three
standard
calculated
replicates.
deviations
differences among treatments were determined
Multiple Range Test (Steel and Torrie, 1960).
from
All
0
resul ts
means
are
Si9n~ficant
by Duncan' s
New
-
47 -
J
XV.
RBSULTS AND DISCUSSION
i)
rntroduction
~
1he response of the
flame
ionization detector (FlO) ta
acetic F butyric and valerie acids present in different hydrocolloid solutions 15 shown (Figures 1, 2 and 3) for a concentration range of 50 to 1500 ppm.
The response of the FID is
described by the ratio of acid peaJ( height to peaJt hcight of
the internaI
standard for
each VFA
(Figure 1), gelatin (Figure 2)
3).
The function
range
between this
of VFA was
tound
to be
in solutions
of
pectin
and corn syrup sol Ids (F igure
ratio and
the concentration
linear for
each
hydrocolloid
solution (Table 2).
,
The arnount of each volatile fatty acid decreased (Tables
3,
4
and
5)
in
solutions prepared
with
hydrocolloids
solute after freez lng and storage at -20·C for 24h.
Smyrl (1982) have
alsa~repo~ted
dextran solutions
shown
in Table
3,
after
Gero and
los ses of carboxylic acids in
freezing and storage at
significant
and
differences
-20 oC.
(p<O.05)
in
As
the
retention of eâch volatile fatty acid were found among pectin
solutions containing different
In generaI,
pect!n solutions
low rnolecular weight solute.
containing calcium chloride or
potassium hydrogen phthalate showed greater losses of volatile
fatty acids' than solutions prepared with gly'dne 'or sucrose.
This
was
not evident
-
wi th
solutions of
qelatin and corn syrup solids (Tables 4 and 5).
The presence
•
type of difference
..
~
,.
,.tol"".r...poo~-;~
_ _ ~'ll~~""" •
-
....
•
.,
Table 2.
Linear regression parameters for standard eurves of volatile fatty
acide (C2' C41 CS) in solutions of peetin (3% wt/wt), gelatin (3%
wt/wt), and corn syrup solids (5% wt/wt).
~
Hydrocolloid
Correlation
Coefficient (r 2 )
Linear Regression
Volatile Fatty
Equation 1
Acid
,.'1'
Pectin
Aeetic
y =
{5.40· 10- 3 )x + 1.56
.99
Butyric
y
(5.33 • 10- 3 )x + 0.86
.99
Valerie
y ::: (3.63 ·10- 3 )x
+ 0.71
\
.98
H
Gelatin
Corn Syrup Solids
,
Aeetic
y = (5.58 '10- 3 )x
Butyric
y
Valerie
+ 1.26
.99
(6.27 • lü- 3 )x + 0.80
.99
Y
=
=
(4.55 • 10- 3 )x + 0.57
.99
Acetic
y
=
(5.82 • 10- 3 ) x + 1. 31
.98
Butyric
y
=
(5.98 .10- 3 )x + 0.95
.98
Valerie
- y
= (4.41 • 10- 3 )X + 0-.64
.99
y represents ratio oL- a-cid peak height to internaI standard peak height,
represents concentration of volatile fatty acid
x
8;
~.'....,
5
- 49 -
<,1
,
8
>
...<
~
.:"'
.....<
~
Z
::l
"
\J
5
'\
\J
o
ci
lO.
f
-
('1
lHOl3H
J
1 H 0 13H
.'
.~
)i't3d -aiS
)t 't
3 d al::> 't
- 50 -
r
>-
~
...
~
-'"
3
'WI"
..
A
~
f)
V
;.:
•
,
'
~
::1
~
~
,.,.Z
t..J
-1
~
.~
~
,
Z
~
(L
•
....
0
~
0
0
E-t
j
oz
>:-1
!
~
·S j .
0-'"
~ ~
~
~
>Z l
=~,
~
:J
0-"'1
tO
~Oll
·n
1
",ri"
~v
uU
~~a:
~
rIl
ü::l«
~.~
cn~
r-f~
~<).
-
'V ~
N Q ;J
«al>
d
~
~z
ê-tOO
t->-ùJ
Wt-...,J
0
.
QO
II)
....:
~OO
LI)
0
•
CI'
•
U')
::J
lHOl3H
)t 't
3d
-OlS
.L HOl3H
)tv
3d
a I~'t
Cl
i-4
~
<~
/
- 51 ./
1
,
)
t
>,
P
~i
Ir;
i\'
~
.
.~
\
i'
•
,
•
- 52 -
of salts in pectin solution would affect both the growth of
{(
ice citystals during freezing and the electrostatic charge of
y
the pectin Molecule.
~,
~.
"",
~;.
Furthermore, these factors affect the
diffusion coefficient of the volatiles and the location of the
~~:
'~-
i;'),
•
~'
~
~'.',
.
"
~;."
volatile during freezing.
Lambert et al. (1973 a:b) indicated
that a portion of butanol's 10ss from solution during freezing
was
due
to
its
presence at
the
sample surface.
Similar
\
observations were made by Taborsky (1970) who reported that a
large amount of solute or volatile would be found in the part
of the aqueous solution frozen last due to the rejection of
solute by growing ice prystals.
Another source for the loss
of butanol during freezing was attributed to
~he
diffusion of
butanol to cracks at the. interface of the frozen matrix.
/
The
greater volatile concentration at the interface of the frozen
matrix would change the equilibrium between the atmosphere and
'the
in'terface.
The ex change of volatile
from
the
frozen
interface to the atmosphere would favor
vo~atile loss from. the
,
matrix.
The loss of volatile fatty acids would be expected to
ocqur by mechanisms similar to those reported above.
In this study, volatile .loss during storage was not expected to diminish much below the losses found for the 24 h
storage period, because aIl flasks were firmly stoppered and
held at low temperature (-20·C).
Since volatile losses due to
the overall freeze-drying process were generally mu ch greater
than those incurred during freezing 'and storage at -20·C, the
percent retention was determined wi th respect to the frozen
reference.
:,'
.'c
v,~ ~~<"."."
'; ..
~
...-.' .'{.....
1f:"
'-;:;-",~
~
....
....
"
"
.
Table 3.
Retention of volatile fatty acids (C2-CS) in pectin solutions after
freezing and storage at -20·C for 24h.
Percent retention 1 of volatile fatty acid'
Solution composition
,.
98.4 a
98.S ab
(1.2)
(1.9 )
Pect!n (1' wt/wt) Glycine (2' wt/wt)
99.9 8
97.2 8b
(0.7)
(2.0)
pectin (1' wt/wt) Sucrose (2% wt/wt)
99.4 8
(3.3)
98.5 a
pect!n (3% wt/wt)
87.6 bc
90.9 cd
( 1 .1)
(2.2)
(2.5)
Isovaleric
valerie
Average
97.9 a
(2.2)
98.1 a
98.0 a
(2.0)
(2.0)
97.3 ab ,
(0.6)
97.6 a ,
97.4 a
(0.8)
97.9 a
(0.3 )
99.8 a
(6.0)
96.0 ab
(2.9)
98.2 a
(2.5)
98.4 a
(3.4)
88.2 c
89.7 bc
87.8 b " 88.8 c
(2.4)
(3.3)
(0.9)
(1.3)
(2.1)
~
b~
92.S b
(3.6)
91.8 b
(6.0)
85.8 c
8S.,c
84.6 b
85.2 d
(2.7)
( 2.1 )
(2.5)
(2.2)
(2.7)
87.3 e d
91.4 bc
91.0 be
90.8 b
90.9 bc
(8.3)
(6.8)
93.2 bc
93.0 ab
(2.9)
(3.9)
86.0 d
( 12.4 mg/ml)
84.7 C
(4.2)
pectin (3% wt/wtL- CaC1 2
93. 9 ab
pectin (3% wt/wt)
- pH 5.0
pectin (3% wt/wt)- CaC1 2
,
Butyric
(S.O)
- pH 3.0
'"
propionic
16 • 9a
pectin (3%wt/wt)
1
"Acetic 3
(62.0 mg/ml)
93.6 ab
( 1 .1)
92.5
(S.9)
(S.9)
(7.3)
(6.4)
(3.6)
1 Each value represents the mean of three samples ~nd the standard deviation is given
in brackets.
2 values within the same column and which have the same letter are not si9ni~cantly
different (p<0.05).
3 Th~ ,initial concentration of each volatile fatty acid is 600 ppm (vol/vol).
~
c'
t:
,
,.
-. . . "':.:,. "~~'''I~:?-:,..':~~~"t
•
.. ~~:~~~~
..._.;"..- .....,,<~~
.~
.-
-
...~
".
.,
Table 4.
tot.
Retention of volatile fatty acids (C2-CS)
freezing and atorage at -20·C for 24h.
Percent retention 1 of volatile fatty acid
l'
~
"
"
Solution composition
Acetic 3
Gelatin
91;2 a
97.5 a
94.3 a
99.a a
(3.6)
{S. 2)
(4.6)
Gelatin (1% wt/wt) Glycine (2% wt/wt)
91:8 ..
92.7·
95.0 a
(5.8)
(4.1)
Gelatin (1% wt/wt) Sucrose (2\ wt/wt)
96.0 8
(3.7)
Gelatin (3% wt/wt) pH 3.0
Valerie
Average
97.6 a ,
(4.0)
99.2 a
(2.1)-
(3.4)
96.4. b
(1.7)
95.4 a
(3.8)
94.3 a
(3.8)
96.7 a
96.0 a
97.2 ab
95.7 a
(0.3)
( 1 .5)
(1.1)
(2.9)
97.4 a
(2.0)
96.2 a
( 1 .6)
96.0 8
(3.6)
97.2 ab
98.3 8 -7
96.3 8
(1.9)
97.0 a
( 1• 1)
(2.1)
(2.1)
Gelatin (3% wt/wt)
pH 5.0
91.8 a
(5.9)
93.8 a
(4.3)
94.6 8
93.6 b
96.8 a -
94.3 a
(4.4)
(5.5)
(7.3)
( 5.5)
Gelatin (3% wt/wt) Ca~12 (12.)4 mg/ml)
95.8 a
(0.6)
96. la.
(2.0)
95.3 a
95.7 ab
(2.0)
94.6 a
(0.6)
95.;a
('1.7)
Gelatin (3% wt/wt) CaCl2 (6~.0 mg/ml)
97.S a
(1.7)
97.0 a
(2.6)
97.7 a
(3.8)
97.3 ab
97.7 a
(4.4f
97.4 a
(3.6)
1
/
in gelatin solutions after
(3\
wt/wt)
propionic
o
Butyric
(3.4)
Isovaleric
(5.1)
(3.9)
Bach value represents the mean of three samples and the standard deviation is given
in brackets.
2 Values within the same cQlumn and which have the ·same letter are not significantly
different Cp < 0.05).
3 The initial concentration of each volatile fatty ,Cid is 600 ppm (VOl/vol).
.
,
~
) J.
)
~
)
,.
,
k
.
-
-to
-,
j
"
...
.. "
Tllble S.
\
percent~etentionl of volatile fatty acid
1
Solut~on
,
1
compositioQ
90.7 a
Corn Syrup (1% wt/wt)-
93'.0 8
(3.5)
Glycine (2\ wt/wt)
Corn Syrup (1' wt/wt)-
Sucrose (2% wt/wt)
Corn Syrup (S% wt/wt)-
pH 3.0
Corn Syrup (5' wt/wt)··
pH S.O
,
v
90.4 a
(4.2)
•
92.S a
87.6 a
88.3 8
(8.7)
(10.5)
88.,a
?~:B~
91. ,a,
(9.2) "
90.4 a
91.3 a
(7.4)
89.6 a
(6.1)
89.S a
(2.0)
90.1 a
(7.8)
,90.S a .
(6.8'
94.3 8
(7.5)
(8.4)
(4.9)
(6.2)
91. 2 8
91.5 8
(10.5)
(8.1)
90.3 8
(5.6)
92.4 a
96.1 8
(10.5)
93.1 8
(6.3)
95.8 8
(7.2)
93.9 a
(5.6)
92.5 8
(2.9)
93.2 8
C3.9)
93.0 8
(3.6)
91.8 a
(6.0)
92.8 a
93.,a
94.5 8
93.9 8
93.9 8
(8.0)
93.6 a
( 1. 7)
(3.6)
94.6 8
(6.5)
93.4 8
( l . 4)
(3.7)
(2.7)
"(1.1)
(3.0)
Corn Syrup (5% wt/wt)-
95.3 8
(0.7)
92.S a
94.2 a
97.6 a
96.4 a
(3.0)
95.2 a
(3.3)
(5.5}
(3.3)
1 E8Ch value represents the mean of three
in brackets.
f»
(6.2)
Corn Syrup (S% wt/wt)CaC12 (12.4 mg/ml)
CaCl2 (60.0 mg/ml)
<1
------~~----~--~------------------------------------------------~
A~etÎc3 propionic
Butyric
Isovaleric' Valerie Average
Corn Syrup Sollas
(S\ wt/wt)
!
-.
-",
.
Retention of volatill! fattv acids (C2-CS) in solutions of corn- syrup solids
after freezJnq- and storage at -..20·C for 24h. _
~
1\
Il
1
!
~
•
~
sa~ples
".
(3.2)
\
and the standard deviation ls given
~
')
1
2 Values within the same column and whieh have the same letter are not significantly !
qifferent (p ~ O.g~).
.
1.
3 The initial concentration of each vOlatile",fatty acid is 600 ppm (vol/vol).
...
~
)
,
.:>
•
(
VI
,VI
- S6 -
ii)
The
Effect of Solida
Cœpoaition on the R.etention
of
Volatile l'atty Acids.
Low molecular weight solutes were added
solutions to study their effect
on volatile
to hydrocolloid
retention.
As
shown in Table 6, significant differences (p<O. 05) in the retention of volatile
pectin-sucrose,
phthalate.
fatty
acids occurred among solutions -of
pectin-glucose,
The average of
pectin-glycine,
the
retentions
and
for aIl
pectin-.
volatil~
fatty acids in solution was found to be significantly different
(p<O .05)
pectin-phthalate,
pectin-
glucose, pectin-glyc ine and pectin-sucrose (Table 6).
In this
study,
among
solutions
the average of the
of
retentions for aIl volatile fatty
aCidSç"
n solutiqn;
, , was used as an index of volatile retention.
1
This
•
ntion ,index describes
e
the behavior of a
homologous
in solution.
index aIso
~
1
series 'of volatile
fatty
acids
The
provides a measure of the overall effect of each treatment by
taking
tUes
into account
in
solution
the ,preEjence of a large number of vola":',,_
during
freeze-drying.
ThijSS~~' (l91~1) ~~ ~~
demonstrated that the behavior of a homologous series of alcohols
(C2-CS)
mechimism of
in
~todextrin
solutions
selective diffusion.
i~
described by
This mechanism was
the
des-
cribed in terms of a ratio which compared the diffusion coefficient of the volatile to that of water.
size of the alcohols increased,
As t-he molecular
the diffusion coefficient of
the alcohols decreased in each of the maltodextrin solutions
prepared
to
decreasing
moisture
levels.
The
decrease
in
~I""'~' ~ _~
",
~"'f~",,;-"iV ~,,~..,~"I~'r~~~'~·~
)
.~-;;.~
I--~':
/
~
~
•
,
~
i
~
•
~
t
'fabl. 5.
~
..t.ntion of .olatll. fattr acid. ,C2-CS' .ft.T fT ••• e-drylng
.olution. containlng addlt onal .olut••
Solution ooapo.itlon
fi vt:/wt)
PecUn
hoUn
(n,
Ac.tio
21.4· l2
(4."
46 ••e
proplonio
23.7'
'6.0'
autyrlo
Jeo.al.rio
Val.rie
Ay.rag.
40.,lOd
( •• , »
co.t b
55.,e
('7.4)
(7.0'
CO.6d
(5.1'
70.lb
l7.t·
(1."
.S.Ib
(1.2'
61.0 b
(2.0'
23."
(O.ll
17.2'
U.t(
tI.S'
27.,f
41.1 0
(O."
... t a2
35. ,cl
(3.2)
(3.16
Pectin ,'l'-Gluco,, '21'
c
n.'
(1.4 )
51.5 0
(2.2)
7J.,b
(3.7\,
l7.sa
(3.6 )
Sucro •• (21'
71.2 b
59.,b
41.9 0
(6.2'
(6.4'
(5.2)
Oluco.e (2t,
"
Pectin ('I)-Sucro.e (21'
Glycine (2.,
"
Percent retention of YOlat11. fatty acld. (t,
'
(1.')
(lt)
peetin Il''-Glye1n. (2')
Phthalate
(2\)
~ctln
10.7'
IS.S·
90.2'
'6.1)
(l.l»
Il.6)
ll.19
I.2g
5.39
(0.1)
(l.S,
".7'
... lab
6II.tb
(l.2)
(1.')
31.2 d
]6.S·
(4.9)
SO.2 e
(].6,
91.9 a
( 1 .0)
94.S·
(1.7)
Il.6'
4.6 f
(0.2'
5.0 h
(0.5'
7.0 h
(0.5'
(J.7)
(S.3)
(3.2)
, 1 .1)
(0.5'
34.6d
36.6d
(3.1)
tO.lad
(0.2'
n.6 c
45.ad
41.1 d
( 1.1)
17.2 f 9
11. ef
14.; t
13.le
(1.0)
',cttn ("'-Phthalat. (21' 25.5·
(1.2)
(0.5)
(0.4)
(1.1)
11.39
(0.5,
( 1 .0)
15.29
(0.8)
25.0'
n.3 d
33.3 e
(6.6)
SI.l c
(1.6)
/2S.5 f
(0.5)
( 1 .2)
(6.0)
(0.6)
(D. 8'
B.ch v.lu. repre.ent. th. . .an of thr.e .a.ple. and the .t.nd.rd devi.tion 1.
given ln bracket.
2 v.lue. withln th • .... coluan and whlch h ••• the •••• l.tt.r .r. not
.lgnifieantly different (P<O.OS)
l The initial concnetT.tlon of .aeh .ol.til. fatty aeld 1. 'OO,~ (.ol/vol,.
:J)
)
r
"
VI'
.....
•
i,
- 58 -
1
diffusion
of
volat.ile~
in
solution
due
to
an
increase
in
molecular size, wi 11 cause an increase in volatile retention
during freeze-drying.
Gero and Smyrl (1982) have shown that
"
the retention of volati le fa tty ac ids in freeze-dried dextran
.~~
{.
~
.
,'f'
\
i5 greater for propionic acid as compared to acetic and formic
acids.
of
In
this.,~study,
increasing
the retention of volatile fatty acids
molecular size
was
observed
to
freeze-dried pectin and pectin-solute solutions.
in the average of the
increase
in
An increase
retentions for aIl the volatile fatty
..
4cids in solution would reflect an increasing
trend
individual retentions of the volatile fatty acids.
for the
The magni-
tude for the average of the retentions indicates the influence
of
each
treatment
on
volat ile
retention.
'The
beneficial
'f '.
influence of adding sucrose to pectin solutions la shown by
comparing the average of the retentions for aIl volatile fatty
acids in pectin-sucrose solution to that of the pectin s01utian (Table 6).
These retention indices reflected the trend
of the individual retentions for each fatty acid present
pactin solutions after freeze-drying.
1
r
in
The retention index was
also used ta describe the average of'the retentions for l'Ill of
the volat i le fat ty ac ids (Table 7)
in solutions of gelatin,
gum arabic and corn syrup solids after freeze-drying.
The combinations of glycine or phthatlate with any of the
hydrocolloid solutions (Tables 6 and 7)
resul ted
in
a
lower
•
average of the retentions for a11 the volatile fatty acids in
solution.
Bellows and King (1973)
~/'
t'
reported that hydrocol1oid
J
'
•
~.
1
r
- 59 -
Table 7.
Average retention of volatile fatty acids (C2-CS)
after
freeze-drying
8olutions
of
gelatin,
corn
"
syrup solids and gum arabie containing additional
solute.
Avera~e Retention'
of Volatile
Fatty Aeids
solute Composition
(, wt/wt)
Gelatin
Gelatin
Gelatin
Gelatin
Gelatin
Gelatin
( 1%)
(3t)
(lt)-Glueose
(2\)
/
(lt)-Sucrose (2')
(l%)-Glyeine (2')
(l%)-phthalate (2')
GUJIl4 Arabic
Gum Arabie
Gum Arabie
Gum Arabie
Gum Arabie
Gum Arable
Corn
Corn
Corn
Corn
CorQ
Corn
"
............
Syrup
Syrup
Syrup
Syrup
Syrup
Syrup
(là )
-
50.8 *12.,ab
2
46.1 c9.l b
26.0 • S.O.Ç
67.,'.22.0 a
34.0
47.1
-
='=
='=
b
1.6 ~
3.5·
48.1 ='= S.Sc
81.2 ... 2.2 a
69.6 '" 3.0 b
a
82.9
(1 %)
(3%)
(1%)-Glucose (2')
(1%)-Sucrose (2'>
(l%)-Glycine (2')
(l%)-phthalate (2\'
.'0.6
57.0 ... 1.6~
38.5 • 4.2
(1 %)
(3 %)
35.1 .. 5.6c
71.6 .5.1 a
74.7 '" 2. Sa
71.8 .2.9 a
(t%)-Glucose (2')
(t')-Sucrose (2%)
(lt)-Glycine (2%)
(l%)-phthalate (2')
55.4 :t 7.6 b
36.2 • 1.2 c
;
"~"
Y
'..,...-g4Ch - value. _represents an av'erage of' the retention for eaeh
of the fatty acids
2 Values for eaeh group of hydroeolloids whieh have the same
letter are not 'significantly different (p < 0.05)
.
w ,-.
~
_ _ - ... ,.
•
_-IW_- _... __
~
... _" ........
.
3 The initial concentration of eaeh volatile fatty aeid ls 6do
ppm (vol/vol).
.....
...
~.
..
~
....... --,...
- 60 -
solu~ions
prepared vith either amino acids
experience a decrease in the collapse
reflect a new but
namic equilibrium for
soHds
form, the freeze-dried matr ix.
lowered
"
and
the
would
A lower
temperature.
collapse temperature, would
the
or salta,
lower thermody-
concentration
required
to
1 f the collapse temperature ls
freeze-drying
conditions
are
maintained,
structural collapse of the CAS would occur in the model soluThe occurrence of
tions.
adversely affect the
solutions
volatile
structural collapse \'las
retention of eth}"l acetate
(Bellows and King,
fatty
acids
sho\'m
to
in sucrose
The poor retention for
1973).
in aIl hydrocolloid solutions prepared
with phthalate or glycine is attributable to the occurrence of
•
.,.
st~uctural
collapse in the freeze-dried solids matrix •
The binary combination of sucrose
ahowed a
superior retention for each of the
acids when compared
wi thout
and pectin
solute.
to those of a
Ofcarcik
volatile fatty
pectin solution
and Burns (1974)
(Table 6)
showed
prepared
that \r,h0
addition of sucrose to a lactose solution exerted a oynergiatlc
effect on the retention of pyruvic acid.
( 1957)
reported
stabUity of
that
the
addition of
the pectin molecule
Whistler and Corbett
sucrose decreased
by reducing
around the negatively charged carboxyl groups.
the
the
hydration
The presence
of protons from the dissociation of volatile fatty acids would
neutralize the negatively charged carboxyl groups and promote
8ggregation
.a
t
(>
i'
of
the
pectin
molecules
(deMan,
1976).
The
ramified networJe 'of partially assotiated, partially hydrated
micella
(Hodge
and Osman,
1975)
from pectin molecules would
/"
- 61 -
1
1
lncrease solution viscosity and decrease the diffusion
r~te
of
volatiles durlng both freezing and drying.
Thus the combined
effect
from
and protons would
result
in an
drying.
the presence of bath sucrose
increase
ln this work,
in volatile
retention during
the pectin-sucrose combination
freeze(Table
6) showed a beneficial effect on the average of the retentions
for all volatile fatty acids in solution.
Rowever, the bene,
Hcial
influence (Table 7) of adding oucrose to other oolu-
tians of hydrocollolds such as
syrup sol ids,
!
!;laS
retention
of
retention
for
gum
arable
and
corn
ShO\<1O not to be as pronounced on the average
volatile
fatty
The
acids.
these combinations' of
lower
-
sucrase
indices of
point
ta
the
,-_,Jmportance of the interactions between hydrocolloid and solute
ln eorming the freeze-dried soHds matrix.
(1973)
Bellows and King
have stated that large molecules such as gelàt.in and
pectin are capable of
intermolecular cross-linldng.
Inter-
molecular association between hydrocolloids \'iould promote an
increase ln collapse temperature by increaslng the viscosity
of the
CAS
during bath freezing and drying.
solution viscosity would
enhance
volatile
Any increase in
retention
during
freeze-drying.
The presence of different types of solute will affect the
size and the shape of the platelets found in the solids matrix
after
freeze-drying.
The
freeze-dried
solids
matrix
of
different hydrocolloids and combinations of hydrocolloids with
1
"
- -- ~'-
solute, wa!:f examined by scanning electron microscopy (Figures
4-:9) •
The platelet structure was observed in solutions of
62 -
,
l
!-
'.
,
r"
~'
t
r
,
Figure 4 Scanning electron micrograph of a freezedried solids matrix containing pectin(l% wt/wt)
and sucrose(2% wt/wt).
1
)
Scanning electron micrograp
dried solids matrix containing gelatin(3% wt/wt) •
- 63 -
Figure 6 Scanning . electron micrograph of a freeze-'"
dried solids matrix containing gum
arabic(3% wt/wt).
\.
Il
,1'"
o
-
Figure 7 Scanning electron micrograph of a freeze- ,
dried solide matrix containing pectin(l% wt/wt)
and glycine(2% wt/wt).
"
~.
----------
,
,-
9 ....
...
"
". J
,,
Scann1ng electron m1crgraph of the
solids matrix containing pectin(3% wt/wt) and valerie aeid(l% v/v).
~
,
~.
"
,.
"
..
...... ~
.'
~V r...:.-r~'F-""~ ~~~M"'''''''''~$",''''l
*,
~ ~ .. j"'
.. ,
1
J.... ,~
.:,,~
-
-
--
•
.
.
solids matrix containing gum alabie(3% wt/wt) and valerie ae1d( 11tY/v).
(JI
VI
-'
~
.\
-------
"
pectin-sucrose
(Figure
4),
gelatin
(Figure
5),
gum
arabie
r
(Figures 6
and 9)
and pectin
(Figure 8).
Flink and
Gejl-
Hansen (1972) also observed the platelet structure byelectron
microscopy in the solids matrix of freeze-dried maltodextrin.
A different
type of platelet structure (Figure 7) was 06served
,.
for the hydrocolloid combination of pectin and glycine.
difference
,,
The
in platelet structure indicates the importance of
type of solute in the formation of
the solids matrix during
freeze-drying.
The
molecuiar
examined by
assocJ,ation
infra-red
analysis
in
pec,tin
using a
solutions
calibration
file
was
of
water (Figure 10) which ran in tandem with a sean of pectin
dissolved
\
in water.
The inte...uolecular association between
pectin Molecules was examined in pêetin solutions p~epared to
different concentrations by infra-red analysis
(Figures 11 -
F
13).
An
evidence
5.76~)
increase in
of
shifting
the concentration of pectin showed no
for
carboxyl
or hydroxyl group bending
group
stretching
(7.4-7.9~).
Any
sh~ft
(5.71-
in the
bending' or stretching of the groups would be interpreted as
sorne form of molecular association.
tion
between
pecti'n
and
\
low
Intramolecular associa-
molecular
weight
examined in pectin solutions containing sucrose,
solute
was
phthalate or
,
glycine by infra-red analysis.
,NO
boxyl group stretching (5.71-5,. 76}J)
shift was observed for carwh en sucrose (Figure 14),
phthalate (Figure 15) or glycine (Figure 16) were added to the
pectin solutions.
showed an
The pectil1-sucrose solution
(Figure
14)
increase in absorption in' the reqion of hydroxyl-
"
r
,
"t
g
-: 68 -
'b
.
-
•
0
"1
\..
.
"
•
-
~
"~
v
~
1.
, ..
r-
,
~
~
i
i
,
ï',
~
~
"'{.
0
• ri!
'.
>
~
~ fit<
0
.
,~
.
1
.
Eo4
orzl"·
-
~
(c
~ï '
N
...
N
.
"
...
1
~
<0
~o
~
~t
..
~
I~
~
U')
,
il
~~
.~.!I
.
,
Q~
OP
~
~
~
'"
)'
•
,
-
'.
.
.
.,
"
- 69 -
q
-
"
1
,.....
~
.-:-
V
~
i
~
.'
,
..
<
:
~
~
CI
,
~~
0
r.c
0
1
0)
,...:
' ,
",>
~
~
~
.
'"
~
r:1
:>
"
~
.,
r"
1'''- ~
o•
~;
,3
m)
rtl
!
,;"
,..
'il
•
C\I
N
~
V.
~o
co
1-1
~~
...
..:1
,
\
.r
~~
,....
~
ld
r
~
ra.
8
-
( % )
~
:!J:>NV ..L.L1:WSNVU.J..
.---
\
J
,
oN
o
o
co
,
~,'
{'
.
-
\'
!).
-
"
0
-
.
\
- 11 -
0.
-
o
"
~ ,~
JJ
C')• V
~
i
~~
1
~
>
Z
0
~
~~
i~
~ <"",
S~
Î~
~
0)
1
il
1'-
,
!~~
'~
O~ "
1
~
~VZ'
ta Z 3
t-I,
g oiJ
~
~O 3
-q;
t~
<0
1-1
,,~;
/
/'
Z'"
t-I
Z rzl.
I-IUl
~<
i
~~ 0
1'-
LO•
•
~8~'
0
1-1'
f&.
--~,
,
(,~
0
<Xl
~
:ol~NV.LJ. IWS~ •• L
~
0
C\I
q
U')
./
/'
.
-,~\~,-;t'
~..".' t-,...."..,~\ -
\-
,~
.--
~
-
.,
..
â
'.
,~,
~
\
"lŒf
l
~
v
-
-
--t'
~....
~.
.. """
.~~<
/'
r---
\
~....-fl!'.-:"\
t
'"
~
~ SO· /
r.
~
H
r
l
SO.-
'"
"
~
r-
,1-
..:.1oJo
40
t
C
2
""
,
t
5.0
5.7
il
FIGURE
15
INFRA-RBD
. CONTA:I:N:I:NG
PHTHAI..ATB
7.9
7.2
SPECTHUM OF
PBC-r:I:N
(12'"
9.4
WAVBI..RNGTH
(~
...rt;/...,t)
~t/~)_
fi
A
()J)
SOLUTroN
.AND
lOD
-.J
N
,
,.....
t
t'''"
~
l...
0 ....
~
'"
,j'
~
"»1
v
•
r:J
f
{
o
~ 80
f0r....
..
----
I
~~
z
r:<
r-:'
~40
20
l i ,
5.0
5.7
6..4
,
,
7.2
7.9
t~7
'9.4
WAVELBNGTH
FIGURE 16 INFRA-RED SPBCTHUM O~ A SOLUTION
CONTAINING PBCTIN (~ ~/~) .AND
GLYCINE: (12'110 ~/""t)_
\
,10.0'
()J)
.....
w
\-J
,
- 74 -
group
bending
which
18
explained
by
the
contribution
of
absorption from hydroxyl groups of sucrose molecules.
These
between
pectin
results
suggest
molecules and
that
molecular
low molecular
as.sociation
c;
\'leight solute
is
not
ionic
in
nature but in the form of hydrogen bonding.
In
this
study,
the addition of hydrocolloids
increased
volatile retention by preventing structural collapse of
<
solids matrix during
freeze-drying.
the
The add i tion of hydro-
colloids such as pectin would increase volatile retentlqn in
frui t juices by preventing structural collapse c of the sol i,ds
matrix during
freeze-drying.
.
.
sucrose
demonstrated
a
'"
combin~ion
The
beneficial
effect
by
of pectin and
enhancing
the
,
retention of volatile fatty acids.
\
When phthalate or glucose
was addèd to the hydrocolloid solutions, volatile
/
deerersed due
'
struc{~~~"l
the occurrence of
retention
collapse during
freeze-drying.
\
Iii) 'l'he Bffect
of
pO and Ionie strength on the Retention of
Vol?tile Patty Acide.
The effects of
solution acidity and
volatile retention i.n Golutions
ionic strength on
buffered "it.h potasàium hy"
drogen phthalate to different pH Y'alues (pH 3.0,4.0, 5.0, 6.0)
\
were'examined
after freeze-drying.
The average of the reten-
tions for each of the volatile fatty acids in solution was
. . i _
used as an 'index to evaluate volatile 1055 after freezedrying.
~mong
Signîficant differences (p<O.05) (Table 8) were shown
solutions buffered
to pH
values of 3.0, 4.0,
5.0
and
,
'.
-
Table
8.
Average
7S -
retention of volatile fatty acids (C2- CS)
after freeze-drying aqueous solutions adjusted for
pH by a phthalate buffer.
Average
Phthalate Buffer
Retention 1 of
Volatile Fatty Acidl..'
(% )
11 .2
:1:
3. 7 a2
pB 3.0 4
12.8
i
5. 4 a
pH 4.0 4
12.6
i
2.3 a
pH 5.05
79.4 i
4.S b
82.7
6. Ob
~bthalate
salt solution3
'pH 6.0 5
.'
i
1
Each value represents an average of the retention for each
o~ the fatty acide and the standard deviation
2 Vall,les
which have the same letter
different (p < 0.05)
.;
3
Pht~alate
are
not
significantly
buffer solution (pH 4. 0)
4 Phthalate buffer solution was adjusteè with p.1N HCI ,
5 Phthalate buffer solution was adjusted with O. lN NaOH
(
\
- 76 -
6.0.
The high losses of volatile fatty acids in aqueous solu-
tions buf6ered to pH values of 3.0 and 4.0 are attributable to
the predominance of the unionized form of the acid.
In con-
trast, the elevated retentions of volatile fatty acids
8)
(Table
in aqueous solutions bufféred to pH values of 5.0 and 6.0
are attributable to the
the fatty acid.
"HIe
and
whereas,
higher propOrtion of ionized form of
The unionized form of the fatty acid is vola-
would
be
~rom
lost
solution during
the ionized form of
fatty acid is not volatile and
consequently would be retained.
acids
which
occurred
in
freeze-drying:
The los ses of volatile -fatty
aqueous
solutions' ,bu'ffered
to
pH
values of 5.0 and 6.0 are attributable to the small population
0\
\~
of fatty acids in the unionized forme
acids
in the unionized
expected
as a
occurs for
large
result of
at pH values of 5.0 and
the
dissociation
6.0
equil ibrilJIU
in
solutions
retention
puffered
for
to pH
volatile
values
fatty
of
5.0
is
which
fatty acids in aqueous solutions (Table 11) •
increases
aqueous
form
The presence of fatty
The
acids
and
in
6.0,
indicate the overriding influence of the ionized form of fatty\
acids on volatile
The
effects
...
~etention
of
during freeze-drying.
adjusting
solution
strength on' volatile retention were
colloid
solutions
(pectin,
gelatin,
acidity
ahd
also examined
and
corn
in
lonic
hydro-
syrup solids)
,
after
freeze-drying.
AlI
the
hydrocolloid
solu tions
were
}
buffered with potassium
3 • 0,· 4. 0 ,
5 • 0,
and 6.0.
hydrogefl phthalate
to pH
Significant differences
values of
(p<O. 05)
in
"
the average of
the retentions
for volatile
~atty
t
r"
acids were
1
- 77 -
....
Table 9'
Average
after
retention of
volatile
freeze-drying
pectin
fatty
acids
sol utions
(3%
(C2-Cs)
wt/wt)
r'\
adjusted for pH and sodium chloride content.
pH
Sodium Chlor:ide
(9/10 mL}'
6.0
6.0
0.00
0.05
6.0
0.10
0.15
6.0
1
"
(,)
76.6 ± 5. 4 a2
62:5 :!: 8. 1 abc
63.9 :i: 8. 9 abc
72.3
.1:
8. 1 ab
5.0
~.O5
0.10
79.8 ± 9. Oa
51. 1 ;f: 3. Scde
42.4 ±15.7 def
5.0
0.15
50.8 '" 6.4 cde
4.0
4.0
O~,OO
,
0.05
55.9
39.9
4.0
4.0
0.10
0.15
37. 1 :1:
51 .5 :i:15.6 cde
3.0
3.0
0.00
0.05
50.7 ±11. 2 cde
30.0 t 6.9 f
3.0
3.0
0.10
0.15
39.0 ± 9.1 def
34.8 tlD.S e f
5.0
5.0
1
Average Retention1
of Volatile
Fatty Acids
0.00
:1: 10.
:!:
3 bcd
6.7 def
7.S ef
Each value given with its standard deviation represents an
average of the retention and i ts standa1d deviation for
each fatty acid.
2 -Values which
different (p
have
the same
< 0.05)
.--....
. -
~
letter are
not
significëlntiy
.~-
\.
)
•
,.
- 18 -
"Table 10
Aver4ge retenÙon of
after' freeze
drying
volatile fatty acids
gelatin
(~,
solutions
(C2- C S)
wt/wt)
,adjusted f~H and sodium chloride·~ontent.
Average Retentionl
~.()latile
C
Sodium Chloride
(g/10 mL)
pH
Fatty Acids
(' )
80.3 :t:13.1 4 1:>
2
6.0
6.0
0.05
6.0
O. 15
85.1 • 6.94
84.4 ... 6.0 a
5.0
0.00
77.2 '. 6.0aoc
5.0
5.0
5.0
0.05'
0.10
0.15
62 • 8 ± 1 2 • 5 be d e
4ef
55 .0 ±16.9
15. 3 ± 8. 1abcd
0.00
56.1 ± s.a c4 • f
'50.2 :t:21.0. f9
0.00
,.
0
4.0
4.0
4.0
0.·15
4p.5 ±12.9 f9
3.0
0.00
3.0
3.0
0.05
0.10
3.0
0.15
36.4 ± 5.3!9
Ir
29.5 3: 8.8 9
... 6.6 efg '
39.3 :i:: '8.7 fg
0.05
0.10
38.6
III:
8.7 f9
Ç"7
1
Each value given with i ts standard deviation represents an
average of the retention and its stan,dard deviation for
each fatty aci~.
\
2
Values which have the
different (p < 0.05)
J
/
same
letter are
not significantly'
"
- 79
1
Table
11
Solubility
and dissociation
constants1
2
for
volatile fatty acids in aqueous solutiotls.
Acid
Structure
"
,$
;'
-. CH3COOH
Aceti'
':.,...
l,
c:.o
t
1.76 x 10- 5
1.34 x 10- 5
propionic
CH3CH2COOH
ClIC)
n-Butyric
CH3CH2CH2COOH
OC)
1.54 x 10 ... 5
Valerie
CH3CH2CH2CH2COOH
S
1.51 x 10- 5
Isovaleric
(CH3 ) 2CHCH2COOH
S
1.70 x 10- 5
;'
~
Ka 4
1~;POlubilïty
"
"
LI
1 Weast, 197ï
2 €halmers and Watts, 1972
,
3 S-Slight
sol~ble
1
infinitely soluble
00
4 Acid dissociation constant
.,
\
•
!, ......
0
~
~.
'0
7'"
shown-among solutions buffered to pB values
3.0and6.~
pectin and gelatin solutions (Tables 9 and 10).
The
80 -
for both
pr~domin-,
ance of the unionized, more volatile form of the acid at pH
values
of
3.0" and
4.0
would ,~xplain
the decrease
.
!volatile fatty acids
'\
average
of
the
retentions
for
in
the
'
during
\
freeze-drying.
No significaJ;tt differences in the average of
the retentions for volatile fatty acids vere shown among solutions buffered to pH values(Table 11,) 3.0, 4.0and 5.0 for corn
syrup solids.
.'
of dissolved
Flink (1975) indicatc!d that ,the higher content
solids and
the
type of dissolved solids were
parameters which influenced volatile retention during freezedrying.
The higher initial dissolved aolids content of corn
ayrup (5' wt/wt) aa:comparedto thelOther, hydrocoll o 1ds (3' wt/\.rl),
retention~
.ay account in part for the hiqher average of the
for
volatile
Purthermore,
fatty acids during
the
ability of
1
freeze-drying
corn syrup solids
(Figure
1
17).
•
to assoclate
intermolecularly due to both the small chain length and the
'presence of hydroxyl groups on the sugar moleclues May a~coun~
(;
for part of
the increase in the retention of volatile fatty
acids durtng freeze-drying.
Further evidence of the effect of
initial dissolved solids content is shown in Figure 17 by com,~
Il
paring the average of the retention of volatile fatty acids
~n
that of buffer solution~'
)
prepared to pH values of 3.0 and 4.0. The increase in vola-j
buffered hydrocolloid solutions
to
tUe fatty acid retention indicates that the presence of dis..:.
."
s01ved 501id5 reduces the 105S of fatty acids during freezedrying.
,
..
"
.-,
. '.
..
.......,:..
.
~
.
~'::
')
,
-
~an'
-,
"-'
•
B- PHTHALATE
Z80
,
:..
Z60
'"
~
1
,
W
~50
1
~40
..
wO~
.
BUFf"ER
.1
....QJO
20
P- PECTIN
B "'"
OLIDStB--
Il Il l,. IBI
lOtl_ Ir.pH 3.0
~
t
<:rGELATIN t8.'."
c- C§0RN SVRUP .
"
1. 1.
pH 4.0
pHS.O
II'
.'
pH 6.0 -
'b
~
I··IGURE
..
17
AV,ERAGE
RJ4-:TENTION
OF
TI ni!
VOI.. ATILE FArr-rv ACIDS(C2- C 5 ) '
IN HYDROCOI. T"'<Y.LI> SOLUT;I.ON$
RUF ......ER..~D
"
TO
DTFFERENT
pH
~
.
....
QI
VAI.. UF.S.
., '.. .........
..
,
/'
The effect of
ionie strengt;h on volatile retention was
examined by monitoring the average of retentions for votatiie
fatty
aeids
in
buffered
hydrocolloid
solutiofis
different amounts of sodium chloride.
molecular weight solutes such as sal t
The
containing
add i tion of
to hydrocolloid
tions has been reported by Bellows and King (1973)
structural
eollapse
during
freeze':drying
and
'decrease the retention of volatile fatty acids.
low
solu-
to promote
consequently
i
Bowever, the
?
higher
tile
"
average of the retentions for vola-
(Tables 9 and 10)
fatty
aclds
in
buffered
hydrocolloid
solutions
as
compared to that.,f aqueous solutions prepared to pH values of
3.0 and 4.0,
...
i~dicate
proteet~,on
certain degree of
l
during
1
'b)
that pectin and gelatin solution exert a
freeze-drying_
increase
the
molecular
The presence
viseosity
of
association due
..
to prevent structural , collapse
the
to
of hyd,rocolloids
CAS
as a
water
solids during freezing and drying _
result
removal
of
from
would
inter-
areas 'of
•
The inerease in viseosity
of the CAS would affect - diffusion coefficients of
the vola-
.1 ••
tiles
and
èonsequenHy
reduce
volatile lb'ss
(Thijssen
and
Q
Rulkens, 1968) ..
AS
the
ionie
solutions by
chloride,
the
freeze~drying
,
was
addition of
the average of the
acids (Tables
retention
strength
inereased
increasing
in
hydrôcolloid
amounts
of, sodium
retentions for volatile
9 1 ,,10 and 12) was shown to be affected
•
could
Bowever,
-a
....,
not
be
signifieant trend
established
in' pectin
..
or
duri~g
volatile
gelatin
............_--- _....- ...
• ..........
...-
.
for
fatty
.~_
.
"
-.-,\
. ...
, -
... 83 -
1
4
Table 12
Average retentiorf of volatile
fatty
'"
acids' (C2-C S)
-after freeze-drylng solutions of corn syrup Bolids
(5'
wt/wt)
adjusted
for
and
pH
sodium
chloride
content.
Average R-.tention 1
of VOl,tile
Patty Acids
Sodiua Chloride
(g/10 ilL)
pB
(t)
..
•
~
,
'~
(
,
6.0
0.00
6.0
6.0
6.0
0.05
0.10
0.15
5.0
5.0
0.00
0.05
5.0
0.10
5.0
0.15
4.0
4.0
4.0
. 4.0
0.00
0.05
..
89.6 • 1.labc
'88.3 *10 •••bcèl
*
85.8
7.3.bect.
83.6 • 2.1a~4.
82.3 • 5.2abcde
75.3 • 7.1 4ef
3.0
3.0
0.10
~.o
0.15
91.5 • ".9 ab
79.4
2.3 bcd.
67.2. 5.1 f '
60.8 .12.9 9
*
,
0.'15
o~oo
9 .... 7 • 2.,.2
83.2
7,.2·bcèle
*
0.10
3.0
~
O.OS
,
"
7 S • 7 • 3.8 cSe f
7.7 • 8 • 2. 9 cde
73.2 • 2.8 et
56.2 .13."~
1
Bach value given vith its standard deviation represents ah
avera,g.e of the retention and its standard deviation for
each fatty aeid •
.2
Values whicb have
differ~nt
the sue letter !~e not significantly
'(P-<-:O.OS)
..-'
'.
•
-
84 -
solutlon,s preplr"ed with increasing amounts of sodium ch10ride
('l'ables 10 and 11).
vola~ile
in
~hen
retention
these
The lack of any signifieant trend fot'
sodium chloride content ïs increased
hydrocollo.Ld· solutions,
collapse
may
be
freeze-dr1ed
/
occurring
matrix.
in
The
sU9gests
that
local1zed
structural
regions
locaHzed nature
of
of
the
structura-1
collapse is supported by results wh.ich show migration of low
molecular veight
(r._bert
~
al.,
reg-ions where
solute
1973a:
fre~zing
in model solutions during freezing
If solids accumulate in
1973b).
occurs last, other regions
of the
matrix will collapse due to a lov concentration of solids.
Bowever,
,
\
the average of
acids was
chlori~~
not
th~
retentions
for
affected when increasing
volatile
alllounts of
fatty
sodium
vere added to solutions of corn syrup solids buffered
to pB values of 3.0 and ..... 0 (Table 12).
The results from
solutions of corn syrup Bolids suggest the importance of both
type and
•
initial dissolved
•
solide content in reducin9 the
occurrence of structural collapse during
fre~ze-drying.
ExeerilIIental results indicate that the dissociation of
fatty acids to the ionized, non-volatile form is an important
influence on volatile retention
during
freeze-drying,.
The
1
retendon of organic acids during the freeze-drying of
would
be promoted by pB adjustment so as to produce a
population of
acids
in
the
ionized
form.
jui~es
lar~
However,
the
addition of salta çdecreases V'olatile retention by promoting
structural
collapse
in
the solids
matrix
during 'freeZ:~-
'.
l,
i
,
é
---
1
--}------,-•
"
1 "":
~
,,-
85 r,
drying.
Bydrocolloids
show a
SUCo
as pectin Ind corn syrup soUds
protective effect in preventing structural collapse
when lov 1I\01ecuiar we1gh t solute la added.
This effect would
,
be beneficial in
where
freez .... dryin9 juices slich as orange
Iddi tional
pectin
would
ilot' affect
the
juice
colloidal
suspension present.
.'
~be
1'1)
8ffect of !'n!e4Dd AIIOUnt of Volatile
the volatile
OD
~
PattI Acids.
f
:In thls study a homologous series of volatile fatty acids
t-
vas used to evaluate hov the molecular size of a volatile
~
.
~.
" '
v'
f.,
affec~
would
r;~
;
(
:
•
,
retentlon
during
freeze-drying.
1hijssen and ttulkens (1968) have shown that volatile retention
is dependent
"!-
volatile
o~
the diffusivity of the volatile through the
solids aatrix during freeze-drying'.
These authors also shoved
that the cUffusivity of volatiles through the sollds lIIatrix' is
-
-
dependent on the
~hain
length of the volatile.
dextrin solution, the diffusion
coefficie~ts
for a homologous
t~e
chain length of
series of alcohols (C2-CS) decreased as
the
for
alc~hols increas~d
(Thijssen, 1971).
the diffusion coefficients of
lDal todextrin
solutions.
In a malto-
No data was reported
volatile
The diffusion
fat~y
acids
coefficients
of
in
a
,
. hOlllOlogous series of volatile fatty acids would
•
/
as chain length increased.
,.
"
t
'(l
,-.
~!.!.
(1970) have shown
that the logarithm of tl\e diffusion coefficient of a volatile
la proportional to the molec:ula'r diOleter of the diffusant.
J
fi'
Menting
also de.crease
...,_.............
,
~
~_
.
- - --- .- ._.
...
............
,. .
...~..:......-_--~._--, .......-'
-.' ..
-
,
A
o
.
86 -
1
decrease in the diffusion coefficients of the fatty acids i S )
expected to cause an increase in the retention of volatile
fatty acids during freeze-drying.
T,he retention of valerie
/
/
acid (Table '13) was significantly greater than that of acetic
/
,
.
/
acid in aIl of the hydro'colloid solutions. ' Gero and smyr}:
1
J
re~ention
(1982) have also reported that the
:
of propionic açid
. ,
vas greater than that of either aCI'ti.Q or fomic acids in
freeze-dried dextran solutions.
Ba ever, the retention of
volatile
1
~
fatty
acids
during
freez -drying
~iSS'OlVed
consideree! in terms of the type of
preparlng the _ e l solutions.
each
fatty
acid
('l'able
hydrocolloid solutions.
must
Thus,
differed
1
also
solids used in
retentlo~. for
The m1gn1 tude of
13)
be
among
the
four
both molecular size of the
volatile and the type of dissolved solids influence volatile
retentlon during freeze-drying.
The affect of solubility and dissociation of an
al
volatile
in
solutions
vas evaluated
by
monitoring
present as
an
additional
volatile
the
Wh~ valerie
retenUon of butyric acid during freeze-drying.
acid vas
addi~on­
at
éoncentrations (0-1500 ppm v/v), the retention of
increasing
butyri~
acid
(Table 14) in the pectin solutions (3\ wt/wt) did not differ
significantly (p < 0.05).
ences
(p
observed
Furthe~ore, no significant differ-
< 0.05) ilr""the retention of butyric acid vere
Ulong
solutions
of
corn
syrup
solids
(St
•
wt/wt)
, (Table 15).
During both freezing and freeze-drying, the expulsion of
vater fro. ,ragions 'of concentrate would pr,omote the formation
,
\
'1
~~';:::;'t1h'"\~l>~ .. I\,J,,I'.'''~,''''''''r~~~'''~~-',"'fI'l'l'lI~,..t~~, ~ ....... J'><,,~l
..,
~
r-:
~
.
..
~
"
Table 13.
Retention of volatile fatty acida (C2-CS) after freeze-drying
solutions of pectin, (3' vt/vt), gelatin C3' wt/wt), gum arabic (3'
wt/wt) and corn syrup solids (5\ wt/wt).
Retentign 1 of volatile fatty acid (l)
/
..
Solution composition
Acetic 3
pect!n (3' v/w)
46.8 c
( 1 .8)
t8.8 c
(0.9)
70 •.a b
(2.0)
87.9 a
(1.8)
85.6 a
30.lb
50.1 a
(12.3)
6Q.2 a
64.1 a
(6.1 )
;32.0b
(8.0 )
54.9 d
(2.9)
71.0 c
( 1.1)
'88.4 b
64.,b
73.2 a
74.7 a
(2.0)
(0.1)
(4.9)
Gelatin (3' v/v)
Gum Arabic (l'v/v)
~corn
Syrup (5' v/v)
propionic
Butyric
(4.0)
,tto)
~leric
Isovaleric
(1.2)
~(13.8)
..
(11.3)
96.0 a
(2.4)
95.S a ,
7s.2 a
(.6.2)
73.9·
(7.1 )
(1.8)
..
"
1 Each value given with its standard deviation represents an average of the
retention and its standard deviation for each fatty acid
2 Values which have the sarne letter vithin a row are not significiantly
different.(p < 0.05) by 'Duncan'a New Multiple Range Test.
3 The initial concentration fo each volatile fatty acid :i8 600 ppm (vol/vol).
..
~
'---
....
..... " _~ ,-' 0:': ~:;;'- ...~::_.J'i"~,,,~~"'_:~..!.r:."'.. ,~ ~~~ .. ~
"
•~
,
,
~
",
',1
~-
,
.
,
~
(
---
- ~-
,
....--..-
,
'
- 88 .; .
.
Table 14 . Retention of butyric acid after freeze..drying peetin
solutions (3' vt/wt) eontaining valerie aeid as an •
addition&! volatile.
.
volatile .compos i t ion
.
!lutyric Aeid
(pp.)
1
,,' .
("
'
Retention 1 of
Butyrie Acid
(t)
valerie Acid
(ppm)
69.1 z
6.5 a2
600
0
600
300
600
600
6.3 a
63.9 z 10.)4 a
600
900
63.4 z 10 .. 2a
600
1200
600
1500
64.1 z
"
-,
65.1 z 11.7 a
68.9 z 12.9 a
Bach value given vith 1ts ~tandard deviation represents'the
Mean of at least three, samples
'2
iii
,
,
.)
values which ha~ve the saille letter are not signifieantly
different (p < O~OS)
- ·89- -
9
..
.
'l'able 15 "Retention
-l,
of
butyric
acid-
after
.,.._
freeze-drying
solutio.ns of corn syrup solids (St wt/wt) eontaining
valerie acid as an additional volatile.
volatile composition
,
. Butyrie Acid
Retention1 of
Butyrie ~cid ,
Valerie Acid
(ppm)
(ppm)
300
/0
300
90.4 • 6.1 a
900
' 83.1 • 8.1 a
1500
86.3 ~ 7.S a
300
300
"
300
,
(')-
81.9 .11.8 a2
"
"\
~.
'\
1
Each value9iven with its standard deviation represents the
mean of at least three samples
2
Values which have the same
differe~t (p < 0..,05)
'
letter
are
not significantly
..
)
,,
••
.
---,- - -.-. ---' - . - -.. - ..-...
'
- --.
-\--
-~--"-
/
'
\
)
,
---
[
\
t
of
.' .
\1 '
1
secon~ary
a
- 90 -
1
phase
Bexanol, a
~latile
solutions,
wa~
\
tions after
~I
volatile" of
for
l1aited solubUity.
~
which shows ltmHeeS solubility in aqueou8
il
observeeS microscopically in mal todèxtriln Bolu,
fr~zing
(Flink
\
~
al., 1973).
Flink and Gejl-
Bansen (1972) have also stated that the appearance of alcohol
droplets in freeze-dried maltodextrin cakes couleS be related
to
the
solubility
of
volatile
Itayaert
alcohols.
(1974)
"reported that the loss of hexanol
during freeze-dryillg could
,
be estimated by determining the amount of aftermarks pre'Jent
on the platelet surface of a tt (wt/wt) dried gum by electron
.
'.
seanning
'
In this study,
microseopy.
freeze-dried
cakes of
pectin and gum arabie contain'ing valerie acid were examined by
scanning electron microscopy.
As shown in Figures 8 and 9,
visible aftermarks were observe<! on the' platelet surface of
,
"
pectin and gum arabie after freeze-:drying.
_-"~"""'l,
Mas~di
,'.,
~
and King (1974b) have shown that the presence of
... /
a aecondary phase in solution vould promote volatile
in9 freeze-drying due te
phases.
1065
dur-
the partition of volatile between
'.
The solubility limit of valerie acid in water Is 30
pplll (Weast, 1977).
valerie acid would fom a secon9ary phase
•
in the fom of dropiets during freeze-drying of· hydrocolloids
solutions if
the concentration of valerie
grea ter
the
than
sol ubi 1 i ty 1 im it.
ts
acid present
During
freeze-drying,
butyrie acid would partition between droplets of valerie acid
and
1·
the
hydrocolloid
containing valerie
solution.
acid,
the
In
hydrocolloid
10s8 of
solutions
butyric aeid during
"
...... . .....
~
\
-..
........... - .....,- ....
_----
r'
,
,
/
1
Table 16
91
Retention of b,ùtyrie acid after freeze-c1ryinq peètin
,
(3',
wt/wt)
eontainlng
volatile
fatty
adds
as
"
additional volatiles.
Volatile Composition
-
primary Volatile"
(600 ppm) ,
t
~
:"....
.
'I
\-L.
';
r
Retention1 of
Butyrie Acid
(t)
Addi tional, volatiles
~,
b2
65 ... 5 • 1.6
45.7 • 2.0 d2
Btltyric Acid
None
Butyric Acid
A~etic
Butyric Ac'id
Valerie Acid (1500 ppm)
76.3
Butyric Acid
Acetic Acid (300 ppm)
Valerie Ac~d (1200 ppm)
77 .2
* 3.0 a
* a:6~
Butyric, Acid
Acetic Acid (750 ppm)
valerie Acid (750 ppm)
Butyric Acid
Acetie Acid (120P ppm)
valerie Acid (300 ppmj
45.9
* O.8 d
-'
, Butyric Acid
1l '
Acid (1500 ppm)
, Acetle Acid (500 ppm) ,
, . propionic Aeid (500 PPIIl)
Valerie Acid (500 ppm)
1
J •
"
f
1
Bach value qi.ven wi th its standard deviation represents' the
Mean of at least three samples
2
Values which have the, same
4ifferent (p < 0.05)
~
~.
f
1
1
f
!~~
,
o
~
t~'#
,
.
,
,
,
......
.
.
_--.~
-- -_ ... ...
~ ~
-
~-
....
-
---~
...
_-- --
letter
are not significantly
/
•
1
,.
- 92
Table
n
Retention
of
butyric
acid
after
freeze-drying
'solutions of corn syrup solids (5. vt/wt) containing
volatile fatty acids as additional volatiles.
voiatÙe Composi tion
primary Volatile
~690 ppm)
-
-
Retention 1 of
'-Sutyric Acid
(t)
AdditionaJ, vblatiles
Butyric Acld
None
88.1:!: 8.9 b2
Butyric Acid
•
Butyric Acid
Aeetic Acid (1500 ppm)
82.1 ., 8.4 c
Aeetic Acid (1200 ppm)
Valerie Acid (300 ppm)
86.8 :!: 5.7 b
r
Butyric Acid
Aeetic Acld (750 ppm) L
Valerie Acid (750 ppm)
Butyric Acid
Aeetic Actd (500 ppm)
~ropionic Acid (SOO ppm)
Valerie Acid (500 ppm)
Butyric Acid
Aeetic Acld (375 ppm)
propionic Acid (375 ppm)
Valerie Acld (375 ppm)
Isovalerlc Aetd (315 ppm)
Butyric Acid
Aeetie Acid (300 ppm)
Valerie Acid (1200 ppm)
84.3
::Ir
4.9 bc
\
\
1
2
Bach value given vith its standard deviation
Mean of at least three samples
Va)ues which
different (p
have the seme letter are
< 0.05)
\1
repre~ent~
\
the
r
y
not Si9n ificJ
\
,
\
,
.\
\
\
:~
...
)
c
,
,
\\'
.'
- 93 -
1
.
freeze-drying .ay be eapl.lned ln part by
the~vaporization,of
butyric acid from the interface between the 4roplet of valerie
acid and the void.
The presence of other volatile
solutions (Table16) was shown to
fatty
acids
in pectin
cau~e
significant differences
•
in the retention of butyric acid during fr~eze-drying.
The
inf~~ence
of additional volatiles on the retention of butyric
aclef can be eaplained in terris of the dissociation constants
•
and the 1I01ecular si~ o~ the v~latile fatty acids. In this
study, acetic and butyric acids were added at
equal concentra,
'<>
tions on a part. per .i11ion (pp.) basls to the pectin solu-'
tions.
Bowever, due to the smaller size of the 'acetic acid
-.alecule, the number of acetic acid molecules wou1d be greater
tban the number of butyric acid molecules per unit volume of
pect!n solution.
A larger number
of acetic acid molecules
would increase the protoQ concentratiof! due to the dissociation of acetic acid to fom the ionized .pecl•• of the acid
and a proton.
. r.IIO••1 of "ater .urinq debydr.tion.
th.
du. te
wou Id
Tbe o•• rall ·incr.... in pro,ton concentr.tion
eventually
diaplace, the di ••ociation equiUbriua of
butyric acid towards a greater Concentration of the unionized
'species
~f
the acid.
The unionized species of butyric acid is
volatile and would be lost during freeze-drying.
butyr~c
acid from solutions of pectin and corn syrup soUds
lorables 1~ and 17)
. 1 ')-.
containing acetic acid
volatile, _ay be explained in part'\by the
aIIOunt of unionized butyric acid.
_____
,_~iW"""""_--"
The loss of
""".V'''''''''~~
as an additional
increase in the
\
Smaller losses of butyric
___
' _ _ _ _ _ _'_'' _____ '' __ '''''____ ... __ . . _._ .......
-
94 -
- acid (Tables 16 and 17) occurred in both'pectin and corn syrup
"
solutiorlJJ containing v~~erid aeid as cOIQpared to pectln and
corn syrup solutions containing acetic acid.
~cular
size of
valerie acid as
AQain the larger
eompared
to
acetie. acid
~Uld reduce the number of valerie acid molecules per uni t~
v~lunae
of hydrocolloid solution.
··f
As a consequence of the
r
~al1er
number of
valerie acid molecules
in solution,
the
effect of averall proton concentration on the dissociation of
.'
butyric acid w,ld not be as great.
Thus, more mOlecules of-
butyric a'cid W~ld exist in the ionize..d fortll which shows no
,
volatility.
~urthertllore,
the negative charge of the ionized
!
1
1
.j-
form May lnteract vith the dissolved soUds and consequently
iapede its diffusion through the concentrated aIilorphous s01u-
!
The diffusion coefficient of the
tion.
ionized
forta would
decrease and consequently increase the retention of butyric
acld during freeze-drylng.
In this study, the retention of volatile fatty acide during freeze-drying vas shown to increase with increasing chain
length of fatty acid.
"
Thus to ensure a full body arol'lla for a
f~?d
product after freeze-drylng, a
processor would add back
'low molecular weight volatlles as compared to high molecular
weight volatiles.
(lurthermor,'t, the presence of' volatile com-
pounds whlch surpass tbeir solubility limit during freezing,
will
fom
drying.
dropleta and
eventually
be
lost during
freez!t-
Volatile 10s8 of thia type must be considered when
supplementing the
n~oÇ'
composition of
both processe4, ,and
--1
formulated foods.
'l,
t
(
.
95
,
Iffect of Calci.. Cbloride
and l'rH'!" 1 late on
I.tention
of VolatUe l'atty Acids
,
,
1.
1
retention during freeze-drying were
average of the retentions
f~r
exa~ined ~~
volatile
Monitoring the
f.atty acids ·in
l~h,
ted of freezing at -20·C in still air for at least
the
wbere-'
as, fast freezing was perfomed by immersion of the sample
,
.-
In~o
liquid air
(~196·C)
•
freeze-dried.
and
~hen
the sample was itlilediately
diff~renc~
As shown in Table 18, a'significant
-
(p<O.OS) in the average .retention of' volatile fatty 'acide was
foùnd
\'
~
hydrocolloid solutions." In this study, slow fr,eezing consis-
1
t-
(j
The affects of both' fast and. slow freèzing on volatile
between- fast
and slow freezing
,
fo~ pecÜn
treatnaenfs
.
.olutlona pr.pared without calciulIl:chloride.
tion of' ·f.~y .cid. was
pr!v~ou.ly ahowQ to d.èr.... wt..ft
7'
dextran
(Gero
and
(Ettrup-Peterllon
frozen rapidly
SIIyrl,
1982) and maltodextrift
!S aL, 1973; l'Hnk and Karel"
.s cOIlp.red
solutions
197Gb)
vere
to a slow. freeling treatllent.
The
higher volatile retention which "'as seen
vi th
ing treatment, is explained by the migration of
microregions during frdeze-drylng.
the slow fra.zs~lids: to/fo~
,The formaÙon
of
aicrO-
ragions would reduce the pemeabil1ty of volatiles through the
soUds matrix during drying (~ollnk and Karel, 1970b).
,
.'
-
_._-_..-.__
.,-,.~--._-,-
-----_._---_..
A
fastlr
,-,
- - - -.... r--
,
-
Table 18
ret~ntion of
Average
96 -
volatile fat~"y acids (C2-CS)
after'freeze-drying pectin solutions (3% wt/wt) con, '\
taitling calcium chloride frozen at different rates.
Average Retention 3
of Volatile
~'atty Acids
(t)
Calcium Chioride
Rate of lo'reezing
, (mg/ml')
Slow l
71.5
:1:
12.4
Slow
54.3
:1: 2.9 b
Slow
48.2 :i: 8.4 bc
Slow
-51.6
:1: 2.S b
40.4
:i:
24.8
.,
0
..
37·2
62.0-
,(L
,
,-
Slow
,
~
7.1 cd
~,L2 :1: 2.7 de
"ast 2 .
0.0·
,
12.4
"ast
31.,9
:1:
7.0 de
...24-.-8
"ast
29.6
:l;
6. Ode
"ast
27.8
:1:
4.2·
"ast
26.9
:1: S.S
..,
37.2
.,
62 ... 0
i
.8.7 a4
Ott·O
e
Sl~w f~eezi'ng rftpresents freezing in still air àt' -20°C (or
,12 h.
.
2 ,Fast ofreezing répresents immersion, in, liquid air (-196°C)
and freeze-drying illlllled~ately .
'.
.•
3 Each value given· vith its st'andard dev.iation represents an
average of the retention and its standard deviation for each
of the fatty aclds
4 values vhich have the' same
different (p < 0.05)
letter
ar~
not significantly
r
"'.:'
,
......... _
...1..
_
,
.
"",
~
.-
_.
__
.-
---~--
-
1
97,-
.......
Table 19
Average retention of
after
freeze-dryino
containing
volati.l...e fatty acids
...,
gelatin
calc tum. =hloride
SO,lu~ns
fr'ozen
(n
at
\
(C2-CS)
wt/wt)
different
rates.
1
Averagé Retention 3
of ·Volatile
~atty Acids
(\,
,\,
Calciwm Chloride
(1D9/lII l,
Rate of "reezing
Slowl
69.5.,.,2 S.l a4
12.4
Slow
68.2' 2 7.2 a
24.8
Slow
40.8 2 3.5 4
37.2
Slow
41.9
Slow
39.0 2 7. 7 d .
"ast 2
67.3
:i:
66.7
:i: 6.~a
0.0
62.0
oC -
{
:i:
,
.
6.9 d
/~
0.0
--:;:
"
-- >
12.4
"ast
3.6 a
•
24.8
"aat
60.8 :t 7.8 b
37.2
"ast
57.2 :t 4.8 bc
"ast
54.8 :t 8.l c
..·.ç--"i,.....
62.0
·f'
".
1 Slow freezing represents freezinc;, in stUl air~ -20·C for
12 h.
2 "ast. freezinc;, represents immersion
and' freeze-drying illllledi~tely
in 1 iquid air
.ft-.
(-196°C)
3 Each value oiven with its standard deviation represents an
average of the retentlon and its standard -deviation for each
of'the fatty ~cids
\
#
4 Values which have the
, different (p < 0.05)
l
same
~etter
are
'
not slgnificantly
J'
\
"
- 98 -
1
'1'a.,le 20
\
Average retention of volatile fat.ty adds (C2-CS")
t7
after freeze:"drying solutions of corn sy:rup solids
(St' wt/wt)
containing
calcium chloride
frozen
at
different rates.
ft
Average Retention 3
of VDlatlle
P.at.ty Acids
, CalciUli Chlor ide
(1l9/_1)
Rate of Freezing
.
Slowl
84.8 .12.8 a4
12,.4
Slow
79.f • 8.,ab
24.8
Slow
79.'
:1:
8.,ab
37.2
Slow
76.4
:1:
7.5 abc_
62.0
Slow
89.,.3 • 2.8 a
0.0
Fast 2
69.2 • O.2 bcd
12.4
rast
70.5 • 1.0 bed
24.8
Fast
0.0
l
•
Ct)
.
37.2
..
62.0
a
-
68.4
• e.s bcd
cd
rast
62.5 :f:l.3
Past
59.9 • 2.8 d
•
.
1 Slow freezing represent8 freezing ln still air at -20·C for
12 h.
2 Fast freezing represents immersion in liquid air (-19'·C)
and freeze-drying immediately
,1
Bach value given with ita standard deviation represents an
average of the retention and its standard dev~ation for eacn
of the fatty a c i d s '
.
"Values whlch have the same letter are not ,significantly
different (p < 0.05)
•
-
...... ~_ ......... , ..
·~
..
--,~.-.
...
~t
~ .....
~
#
_ _ _ . _.. _ _
~~
~--_ .._--~
,
j
\
j
o
.. 99 .
f-reeaing treament permits àhorter tille for the migration of
solids and coosequently forms fewer microregions vithin the
solids matrix.
Thus,
permeability ta
the solids matrix vould show greater
volati~es
during drying.
The lack of any sig-
nificant difference between slow and fast freeaing treatments
iI#
for .olution. of gelatin (3' vt/wt) .ugg•• te
both type
-
'.portance of
and concentration of di ••olve6. .011d.
fOrllation of
.lcror~ ions.
In
.
the
in
the preparation of gelatin
solution., the initial heating and then cooling of the gelatin
solution
~onspecific
_ay cause
bond
ordered segments of the chains.
would
c~oss-bond
formation
between
the
As a result, gelatin chains
and fortll a gel (paul, 1972).
In this study,
oel formation vas observed after coolinO the gelatin solutions.
The formation of a gel by intermolecular association
lIlay reduce the contribution ·of lIicroreoion format'1on by freezlog.
,
This, would suooest
entrapped
-,
vithin
the
that
solids
volatil.s could already
lIlatrlx
befor.
the
be
freezlng
r
treat:11lents- baoan.
retent,ion
Thus, the lack of difference in volatile
batveen freeaino
treatlllents could be explained by
gel formation.
,,
:.i
In
r:0-
this
study,
freeze-drying vas also
f:
the
formation
investiga~ed
of
microreoions
during
by adding a oelling aoent,
v'
"
i
t
~
~,
,l~
• l
•
1
~
'.
,
_"'\0._ . . . ,...... , __ ..
~
'.,
:!
fr ,
,
•
calcium
chloride,
~ctin
to
solutions,
wt/wt).
(3'
T,he
presence of calcium cations. would be expected to neutralize
the negatively' charged 'carboxyl groups of pectin and' promo te
l
'
gelation
by
cross-linking
of
pectin
chains (Whistler and
. ~,
association between pectin
"-".)
Corbett,
1957).
..
.
Tbi~...,.
type
of
viscosi~y
chains would be expected to increase the
of the CAS
1
inc~ease
and oonsequently
\
volatile retention.
The addition of
4ifferent aaounts of calcium chloride (Table 18)
show~d
no
trend UIOng diff.rences in the average of retentions for the
volatile
fatty
slowly.
CaC12
(.
acids
pectin-CaCl2
in
solutions
frozen
Similar results ...JTable 18) were shown among pectin-
samp~es
frozen rapidly.
volatile retention
for
The significant decrease in
pectin
solutions
containing
calcium
cl{'loride (Table 18) as compared to pectin solutions prepared
without calcium chloride, would suggest that salt ls producing
structural collapse ln localized areas of the solids lIatrix
durin~ freeze-drying.
ence of.alt
Purther evidence to support the influ-
in localized .reas ..of
the solide •• trix
ls the
'significant differences in the retention of individual fatty
aclds found among pectin (3' wt/wt), pectin (3' wt/wt) - CaCl2
~
(12.4 mg/ml), and pectin (3' wt/wt) - CaC12 (62.0 mg/ml) solutions (Table 3) durlng freezing.
The significant d1fferences
1
(Table 19) in the average of the retentions for volatile fatty
acids in gelatin (3' wt/wt,),'~"CaC12 (24.8, 37.2, 62.0 mg ml-1)
solutions
1
frozen
slowly,
pr~sence
of
calcium
éOllapse
in
localized
would
chloride
areas
of
'"
-- -.
.....
~.-.-.....--.............
. .. . . . . . . . . . -
_ _ _ . . . . ._
-- ._-
~,,-
-
-
R
-.
~.,..., -'~~f
also
which
the
- . . , . . . .................. , .... _ ... ..
'f
\
be
explained
promotes
solids
by
the
structural·
matrix
during
.....
fl
r.
101
.,
t
1..,
t
;
".
•
freez~drying.
p
~owev~~,;' ttie . influence
"
,
of CaCl2- on fatty acid
r
retention ('l'able 4) in 801utions of gel.tin (3' wt/wtr, gela-
..,
tin (3' w/.,,) - CaC12 (12.4 1119/_1), and gelatin (3' ."t/wt) CaC12 (62. mg/ml) ."as not evident after slow freezing.
behavior
sugge~t
lDay
tpàt
the
This
interaction occurring among
gelatin chains
is sufficiently great to
stabilize the sol Ids
,
,
matr.ix and reduce the occurrence of·'
freeze-drying.
8truc~ural
collapse.during
No difference in the average of the retentions
for volatile fatty acids (Table 20) ."ere shown among solutions'
of corn
syrup
solids cOntaining calcium chloride
frozen slo."ly.
the
that were
This behavior for the retention would suggest
importance
of
the
higher
initial
concentration
of
dissolved solids (5\ ."t/wt) and the type of dissolved solids
,
"
in preventing structuràl collapse of the solids matrix.
A significant
difference
in
(p<O.OS)
the
average
of
•
volatile retention was shown (Table 19) betwen either gelatin
(11 ."t/wt- l ) or gelatin-CaCl2 (12.4 mg ml- l ) and gela~in-CaC12
(24.8,
37.2,
62.0 mg
ml- l )
solutions frozen
rapidly.
This
behavior ·suggests that the interaction occurring among gelatin
chains i8 sufficiently qreat to protect gelatin solutions from
collapsing at
concentration~
lower
CaC12, 12.4 mg ml- l ).
b~~en
of
(eg.,
gelatin-
No significant differences were found
the averages of volatile fatty acids in rapidly frozen
.
solutions of pectin and pectin-CaCl 2
f
r
CaC12
(Table
18)
or rapidly
frozen solutions of corn syrup sol ids and corn-syrup solids-
)
CaC12 (Table 20) •
_
........ ~-r~I ......~..."''V ........ _-................-.. ..
_
_
.
The reduced
............_~_ _ . ,... ,_...,........_ .....
~
........~.-
migration of
,
............... _."
solute d'uring
•
.;
- 102 -
j
f •• t-free.lng
wouleS decre.se
\
collapae during
the
occurrence of
sttuctuJ;al"
t
freeze-dr~ing.
However,
the
presence
of
calcium chloride did not promote an increase in the retention
of
volatile
solutions.
not
fatty
aclds
for
any
of
the
hydrocolloid
This behavior would suggest that thé' calcium is
effective
.
r.qu~red
for
in
promoting
enhancing
".
further
'"
volati'le
molecular
association
re,tention
during
freue-drying •
..
~.
l
t1
l,
•
~.
,.
~
f
t
f.
"
~
}>
;0
i'~
f-..
1
~
:/
1
..
~
~
-\
/
..,.
I
,
•
,
-1
.
';
'\
\
1
li.
'1
..
r·
- 103 -
V.
SUIOIARY AND CORCLOSIOMS
The
r~tentlop
of a
homologo~s
series of volatile, fatty
pectin~
actds (C2-CS) was measured in solutions, of
gelatln,
gum arabic and, corn syrup solids after freeze-drying.
The
influence of solution properties (solute-solute interaction,
pH and
ionic strength,
calcium chloride
volatile concentration) on volatile
concentration and
r~tention
was monitored by
determining the retention of volatile fatty acids.
'l'he presence of sucrose
shown
to
retention
increase
was
volatile
found
to
in hydroeolloid solutions was
retention.
decrease
when
However,
either
phthalate was added to hydrocollold solutions.
volatile
glycine
or
Sucrose
is
consldered a dehydrating agent causing the hydrocoUoid chains
to unfold and increase solution viscosity.
An increase in the
f
viscosity of the solution decreases the volatile' s diffusion
!'
.
coefficient in solution resulting in a greater retention of
1
the vola'tile.
,
'l'he addition of elther glycine or phthalate
,
'~
caused structural collapse in the solids matrix and a decrease
,
i
*,.
.. in the retention of the volatile fatty acids . .
~
;'
The adjustment of solution pB to values of 5.0 and 6.0
i
produced a larger population of ionized fatty acids and conse-
"é~" •
f
;,
quently promoted an
f
increase in fatty
acid retention.
The
,
r
addition of sodium chloride to solutions buffered to different
i
pB values reduced volatile retention.
t
1
\
',.
Bowever, no significant
trend for volatile retention could be established for the con-
l
centrations of
sodium
chloride
used.
This
behavior
was
•
-I~·
"~
.
"
...-
sÙ'ggested to be due to the< localized nature of structural
collapse in the solids matrix, during freeze-drying. -=
/
The presence of additional volatiles at different concentrations was shown to affect the retention 'of butyric acid in
solutions o.f pectin and corn 'syrup solids.
concentration of
volatile 'would 'influence
acid retention by changing bath the dissociation
,f
between
the~
fatty
equi~ibrium
ionized and unionized forms of the fatty acid and
the electric charge on the hydrocolloid molecule.
The reten-
tion of volatile fatty acids d\Jring freeze-drying was demon-
~"< ,
~
additional
An increase in the
-, t
strated to increase with an increasing chain size of the
f~tty
acid.
jL,
.;
.~
For a
pec~in
solution,
the retention of volatile fatty
acids was greater in the sampl.e frozen slawly as compared to
î
~
li
the sample frozen rapidly.
1
centration of dissolved solids and differences in the chemical
;?
Bowever, an increase in the con-
.~
"
i.
composition of the dissolved solids were shawn. to
the
;-,
,
,-
effect of freezing on volatile retention.
the •
€
addition of a gelling agent such as calcium
-
"
"
n •
f
improve the retention of volatile fatty
le,
~
,-t
,
~.
,
~
Fùture studies should investigate the effect
eithèr fatty
~
in
solutions during !reeze-drying.
~
i·
!
a~~ds
acids
or organic acids on
the
retention of
different types of volatiles (alcohols, ketones and aldehydes)
~
~
!
in hydrocolloid solutions during freeze-drying.
(l
Studies of
\
,
this type could then be applied to a food system in order to
/
1
- 1
l,
-
~
...... _ _ · f
• _ _ •• _
...... _
..................
'
.....
L~1
l
--,
- 105 -
{'
t.~
-.
evaluate
.-
,
effect of solution propertiés on volatile reten-'
~he
~uri.ng fre~ze-drying.
t!on
'one of the ahortcomings of this
\
(
study
,l
~as
'not evaluating objectively the amount of structural
collapse occurring in the sol ids matrix.
Since structural
.
,
collapse of ~olids matrix../ during freeze-drying .does' not
c~~~e co~plJte l~sS o~
-;-
1
whi~h
volatiles, any beneficial effect
increases volatile retention should also be evaluated in terms
•
An e~ample
,. of, its effect in preventing ' structural, collapse.
~,
of
t'his. would be to evaluate the effect of
~.
eolloids
adding, hydro-
•
-1
auch as, peê:tin or corn syrup sol Ids
reduce the occurrence
~f.
in' order
to
•
struc'tural collapse and consequently
improving volatile retention in
free~e-dried
•
juiee erystals.
,"
In conclusion, the effèct of solution properties, such as
t,the molecular si:te of
volatile,
the charge of
the
hydro-
colloids and the influence' of' solute-solute interaction h'as
/
/
;
been shown to .affect the retention of .volatile fatty
dü~ing
freeze-drying.
1 .
'
~cids
,
. .
,.
,.
...
..
r .
•
.i
"
('l
)~
--
,'!
•
,.
~!"i,
;r,'
:,(
"
....
~\oo
- ..
...... ,....-#4ft!oI''''-Al./''''
-te• •
_ ... • .....
~....-t
__ •
.a.~...,._
... _ . .
~
•• ., ..
p
....
~
. " ' _ _ _ ~ _ _ . ._
. . ._
.....
_ _ __
;;
~
\
"
;-'
,\
- 106
L~
ft;
1
~
VI.
"-
tJ
RBPBRBRCBS
AMERICAN HAIZE PRODUCTS COMPANY.
Barmond, Indiana, USA.
Alnaizo Powdered Fro-Dex 24',
-
,
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1970. Studies on flavor components'in soybean. Part
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1975.
Mechanïsms of volattle" retention in freeze-dried food
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1942.
The significance of the ·v· X-ray
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/
'
Comple?, formation between starch and.
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1944.
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Maximum allowable operating temperature.
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-.
BELLONS, R.J. and King, C.J. 1973. product collapse during
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(
"
8BNSON, S.W., and Rïchardson, R.L. 1955. A study of hystere818 in thé sorption of polar gases by native and de~atured
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1
~
CBALMERS, R.A., and watts, R.W.E. 1972. Studies on the quantitative freeze drying of 'aqueous solutions of some metabo11cally important aliphatic acids prior to gas liquid
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'Ic'
i
i,
CBIRIFE, J. and Karel M.
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<1
!
,..
"
1
L
{
\
,
~
t.
CBIRIPE, J. and Karel M. 1973b. Contribution 'of adsorption
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,
•
"W....
.
l .. ..,.",.. . . . . . . . .~~ftC_za
_
..................-......:'t
....
1"""·
[
"
'
j'
.
...
,..';r~~~~tIIlJIo'\,..I\"'.....·,..,~OQlW.* ~
~
,
:1
,,<1
,,
- 107 -
CBIRIP~"
J. arAd Karel M.
1974a.
Effect of structure
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,
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"-~
~.
DAMODARAN, 5., and Kinsella, J.E.
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,
'~
ETZEL, M.R. and King, C.J. 1980. Retention of volatile components during freeze-drying of substances containing
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,
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l'
..
. ,
FLINK, j .M. and Gejl-Hansen, F.
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\ \'
\ '
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\
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t
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J. popd
. ---. ---,. --=- -- -~ . . . .~--- ~\ _. -"
\
.....
_--_._,
(
- 108 -
FLINK, J.M. AND Labuza, T. 1972. aetention of 2-propanol at
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"
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c
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.
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"
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~
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~
_...........
(
.'
_._.~
_ ..... '"
~
. . . p. _-.
~
1 ..... '
.. t r _
1
~
,
';;
,
,1
f
'.J~
,.;J",
<
,
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~
~
#
.
•
;'._-;:".~;-."
.~
......
~
' .......- . -r._ ..... _
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\,
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1
~.
'.
.. ..
.
----...
_--_ -..
-'""..
-~----
-
...
'.
- 111 /
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Ilulti-component aqueous
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.\"
,.
f
;1>.
"
•î
TO, 'E.C-. and FUnk, J.M.
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