69.
THEORY OF E E I U L S I O N S
P H Y S I C A L A N D C H E M I C A L N A K E U P O f SAUSAGE E M U L S l O W S
C L I F T O N E.
SWIFT and W I L L I A M L. SULZBACHER
MEAT
LABORATORY
E A S T E R NU T I L I Z A T I O N R E S E A R C H AND DEVELOPMENT D I V I S I O N
AGRl CULTURAL R E S E A R C HS E R V l CE
U N I T E D S T A T E S DEPARTMENT O F A G R I C U L T U R E
MARYLAND
.............................................................
BELTSVILLE.
In comminuted sausage, such as frankfurters and bologna, there i s
approximately 305 f a t ; yet, without magnification, inspection of well-made
products reveals l i t t l e evidence t h a t f a t is a major component. This is
because processing reduces a l l components t o an extremely small p a r t i c l e
s i z e . Fat d i s t r i b u t e d and bound properly a f f e c t s juiciness, tenderness,
and f l a v o r desirably. Fat unbound, o r only partly bound, coalesces during
processing, forming pockets, o r 'lcaps", which is f a t collected between the
casings and the product.
Present methods of manufacturing comminuted sausage, such as
frankfurters and bologna, although l a r g e l y empirical, generally perform
s a t i s f a c t o r i l y , if not optimally. Good judgment regarding the f a c t o r s that
a f f e c t f a t binding, such a s the t o t a l and type of f a t i n the formula, the
type and q u a l i t y of meat, and the e f f e c t s of variations i n processing procedures, i s the p r i n c i p a l a s s e t successf'ul sausagemakers possess. A challenge t o u t i l i z e the binding of r a w materials t o the f u l l e s t extent possible
a r i s e s from t h e competitive nature of t h e industry. However, optimal
efficiency i s seldom obtained; and t h e strongest e f f o r t s t o obtain the most
f r o m materials a r e most prone t o produce unsatisfactory, poorly-bound products. Obviously, t h e development of methods f o r evaluating the f a t emulsifying capacity of sausage ingredients and knowledge of t h e f a c t o r s involved i n
t h e process of f a t binding can provide an improved b a s i s f o r u t i l i z i n g
materials and processing them e f f e c t i v e l y and e f f i c i e n t l y . Efforts i n t h i s
connection have been underway i n our Laboratory f o r several years.
The experimental work presented relates t o meat emulsions prepared
by a process known a s emulsion curing. h u l s i o n curing, as generally conducted, involves 8 o r 1 0 minutes of comminution which converts i c e , lean
and f a t meat, and curing and flavoring agents i n t o b a t t e r , o r meat emulsion.
A recent investigation of meat emulsions by Hansen (1) indicates t h a t p a r t of
t h e f a t i n them e x i s t s i n the form of dispersed globules enclosed i n matrices
formed by protein membranes. These protein membranes are formed by t h e
mechanism f i r s t described i n 1840 by Ascherson who observed t h a t a coagulation
i n t h e form of a membrane occurs inevitably and instantaneously when albumin
comes i n contact with a l i q u i d f a t (2). In t h e ensuing period, considerable
work has been done i n studies of protein-stabilized emulsions; and extensive
information on emulsions i n mayonnaise, salad dressings, and homogenized
m i l k (3). This has provided a background f o r our studies which include work
on methods t o measure the emulsifying capacity of meat, the c h a r a c t e r i s t i c s
of meat-stabilized emulsions, the efficiency of meat proteins a s s t a b i l i z e r s ,
and f a c t o r s t h a t a f f e c t meat proteins as emulsion-stabilizers (4,5)
70
Our preliminary experiments indicated that f u l l employment of the
capacity of meat t o ennilsify f a t requires thorough disintegration and dispersion of t i s s u e i n a r e l a t i v e l y d i l u t e system and t h a t collapse of an
emulsion can serve as an endpoint i n determining t h e capacity of meat t o
s t a b i l i z e an emulsion, provided t h a t s u f f i c i e n t l y viscous emulsions are
formed
,
Then, using the equipment shown i n Figure 1 (Slide 1)
Slide 1
.
: Shows j a r , mixer, graduated cylinder with tubing t o j a r :
I
we studied the e f f e c t s of comminution of meat, dilution of meat slurry,
emulsification a t different rates of mixing, addition of f a t a t different
rates, e f f e c t s of temperature, and the s t a b i l i t y and r i g i d i t y of emulsions.
This atudy vas conducted by systematically varying the following basic method:
50 grams of ground meat were placed in a pint J a r with 200 ml of cold 1 M
N a C 1 solution. The mixture was connninuted for two minutes i n a Servall mimixer. During the operation, the jsr and contents were cooled by innnersion
i n an ice bath. Twelve and five-tenths grams of the resulting s l u r r y were
placed i n another j a r , 37.5 m l of cold 1 M NaC1 were added, and t h e mixture
was mixed f o r a few seconds. Then melted lard o r vegetable o i l was added
fmrn a graduated cylinder and high-speed cutting and mixing was begun. The
f a t was added a t 8 r a t e of 0.8 m l per second f r o m a graduated separatory
funnel through Tygon tubing into the stirred mixture. Elmulsion formed,
persisted, and f i n a l l y collapsed, the t r a n s i t i o n being marked by a gradual
increase, followed by a sudden decrease, in viscosity. Addition of f a t wEL6
inmediately terminated on observation of the abrupt transition. Occasionally
i n routine work, it i s necessary t o change conditions t o increase the
viscosity so that an endpoint is mre pronounced; in other cases, it is
necessary t o manually supplement the m i x i n g of very rigid emulsions with a
piece of tubing so t h a t the mixtures flow i n t o the blade of the Omni-mixer.
The volume of f a t added I s reported as emulsifying capacity, that is, m l f a t
emulsified per 2-1/2 g of meat.
Table 1 (Slide 2) shows the e f f e c t of varying the camminution of
50 g of meat i n 200 m l of' 1 M NaCl. Varying comminution influenced the
ennilsifying capacity of the sample, a maximum being attained with two
minutes of comminution.
7
Table 1, Ef'fect of differences i n t
camminution of meat s l u r r y l Of
Minutes
Usifying
: capacity/2.5 g t i s s u e
a t 13,000 rpn
.
1
2
3
4
ml
137
148
133
131
50 g t i s s u e i n 200 ml 1 M N a C l
-
71
.
Table 2 (Slide 3) indicates t h e e f f e c t of d i l u t i n g the emulsions.
Table 2.
Volume 1 M N a C l
22.5
47.5
100 0
.
ESnulsification a t d i f f e r e n t d i l u t i o n s
.
EInulsifying
capacity
ml
82
1 27
179
.
:
Ehulsion
Semi-solid
viscous, mixable
moderately viscous
The volumes, 22.5, 47.5, and 100.0 m l 1 M N a C l in the left-hand colunm represent d i f f e r e n t d i l u t i o n s of 2.5-gram samples of homogenized t i s s u e i n which
f a t was emulsified. Dilution increased emulsifying capacity from 82 t o 1 2 7
and 1 7 9 m l . Crith t h e lowest d i l u t i o n , a semi-solid emulsion was obtained;
i n 47.5 ml of solvent, the emulsion was viscous but mixable; use of 100 m l
NaCl yielded a moderately viscous emulsion. Increasing the d i l u t i o n decreased v i s c o s i t y and increased emulsifying capacity. J U i n g and detection
of endpoint was most readily accomplished on d i l u t i n g with 47.5 ml.
The data ahown i n Table 3 (Slide 4) indicate t h e e f f e c t of varying
rate of mixing on emulsifying capacity. Decreasing t h e rate of mixing from
13,000 t o 9,200, and then t o 6,500, incressed emulsifying capacity f r o m 142
t o 168 and t o 185. Each of these three speeds produced v i s i b l y d i f f e r e n t
emulsions; a viscous one a t high speed, a slightly viscous one a t medium
speed, and a grainy one a t low speed. Use was made of 13,000 r p m in most
of our work since t h e breaking point of the emulsions produced were most
readily detectable.
Table 3 .
Rate of
Emulsification of d i f f e r e n t rates of mixing
capacity
Description of
emulsion
13,000
142
viscous, mixable
9,200
168
s l i g h t l y viscous
6,500
185
grainy suspension
mixing
rpm
ZhlUlSiQing
ml
Figure 2 (Slide 5) shows the e f f e c t of varying the r a t e of addition
of the f a t t o t h e emulsifying mixture. EhiLsifying capacity was l i n e a r l y
r e l a t e d t o t h e r a t e of addition.
Slide 5
:Shows t h a t emulsifying capacity increased l i n e a r l y with:
:increased r a t e of addition
.
..
72
.
Figure 3 (Slide 6) shows the e f f e c t of varying temperature on
emulsifying capacity. The amount of f a t emulsified 'was inversely and l i n e a r l y
r e l a t e d t o the maximum temperature obtained during emulsification.
Slide 6
:Shows inverse and linear r e l a t i o n of' emulsifying capacity:
:and temperature
.
In view of evidence which will be shown l a t e r t h a t the emulsions a r e s t a b l e a t
7+C, heating i n t h e range shown ShGuld not have caused the emulsions t o break;
m t h e r , assuming t h a t a cause associated d i r e c t l y with the process of emulsification appears mrranted. This might be t h r o w an increased surface area
r e s u l t i n g from an increased dispersion of f a t produced a t higher temperatures,
possibly some denaturation of protein which would then be unable t o form
protective membranes, or possibly, too, production of an a l t e r e d , unstable
form of membrane.
Figure 4 (Slide 7) is a photograph of t h e membranes surrounding f a t
globules in a d i l u t e d emulsion, The membranes formed around each f a t globule
have a non-uniform, polyhedral form. Rigid rnenibranes, such as these, a r e
known t o be more o r less b r i t t l e and have a limited mechanical strength. On
the other hand, they can be heated without breakdown.
.
Slide 7
:Shows stained membranes have noa-uniform polyhedral form:
I
A heated emulsion i s shown i n Figure 5 (Slide 8 ) .
heated 30 min, a t 75OC wtthout separation of f a t ,
Slide 8
This emulsion had been
.
:Shows emlsion t o be r i g i d and s t a b l e a f t e r heating a t 75OC:
I n other work, studies were made of efficiency of proteins in s t a b i l i z i n g f a t emulsions. This involved the preparation of extracts of watersoluble and salt-soluble proteins and then determination of the amounts of
f a t t h a t d i l u t i o n s of these proteins would convert i n t o s t a b l e emulsions.
Table 4 (Slide 9) shows data obtained i n a study of the watersoluble proteins and sodium chloride-soluble proteins which indicate the
amounts of proteins removed fmrn d i f f e r e n t concentrations of p r o t e b solut i o n s t o form insoluble membranes. These exprimrents involved measuring the
protein content of the solution before and after emulslfication t o determine
how much protein had been removed, and measuring the f a t emulsif'ying capacity.
From these data indices of efficiency were calculated, i n terms of ml f a t
emulsified per mg of protein.
73.
Table 4.
Extract
.
Protein efficiency as emulsion s t a b i l i z e r
Protein
: Present
.
:
.. Fat emulsified
.
: Total : ml/mg Protein
:
Used
mQ
$
Water
646
263
60
75
175
1 M NaCl
512
102
80
81
250
145
ml
95
..45
.
48
61
1.75
The efficiency observed with water-soluble protein was 0.45, 0.42, o r 0.48
protein, while that of the salt-soluble proteins was 0.61 and 1.75
i n corresponding u n i t s . Concentration of proteins in the water-soluble ext r a c t d i d not a f f e c t emulsifying capacity appreciably. Variation of t h e prot e i n concentration of solutions of salt-soluble proteins produced an appreciable change; when the proteins were diluted, efficiency increased. The
removal of proteins f r o m solution i n the process of emulsification is
depicted i n the r e s u l t s of u l t r a c e n t r i f u g a l studies.
ml f a t / =
The ultracentrifuge patterns shown i n Figure 6 (Slide 1 0 ) indicate
the amounts of water-soluble proteins and salt-soluble proteins present be-
f o r e and a f t e r t h e solutions had been used in emulsification. Appreciable
water-soluble protein and most of t h e salt-soluble proteins were removed
during the emulsification process.
In work that followed, we f u r t h e r Investigated t h e f a c t o r s t h a t
a f f e c t t h e e m u l s w i n g efficiency of these proteins, p a r t i c u l a r l y the e f f e c t
of varying pH and sodium chloride on both water-soluble and salt-soluble
proteins, t h e e f f e c t s of d i f f e r e n t s a l t s on the e m u l s i e i n g capacity of
water-soluble proteins, t h e e f f e c t s of pH and NaCl on t h e emulsifying
capacity of meat proper, and the e f f e c t of varying t h e water content of
s a l t e d meat on emulsifying capacity.
The e f f e c t s on the emulsiFying capacity of water-soluble proteins
of varying NaCl a t 0,5, 1.0, and 2.0 M concentrations a t pH values ranging
f r o m 4.0 t o 7.85 a r e shown in Figure 7 (Slide 11) The results indicate t h a t
a t a l l pH values t h e emulsifying capacity of proteins increased i n increasing
concentrations of N a C l . Variation of pH had a marked e f f e c t with a maximum
a t approximately pH 5.2 and sharply reduced a c t i v i t y i n e i t h e r more basic o r
a c i d i c solutions. It is notable that water-soluble proteins exert t h e i r
maximum a c t i v i t y a t a lower pH than i s normally obtained i n meat and respond
favorably t o higher concentrations of NaCl than those desired f o r flavoring
purposes.
Also, i n connection with the e f f e c t of NaCl i n a c t i v a t i n g the
emulsifying capacity of water-soluble proteins, we determined t h e emulsifying
capacity of water-soluble proteins a s affected by potassium thiocyanate,
iodide, n i t r a t e , bromide, chloride, and s u l f a t e . The data shown in Table 5
(Slide 1 2 ) indicate that the emulsifying capacity of water-soluble proteins
74
.
decreased i n the order of t h e s a l t s named. This i s the order of the
Hofmeister series and appears t o be t h e s m e ef-fect t h a t a f f e c t s the spreading of proteins a s shown i n the previous studies of others (6). In i n t e r preting t h i s e a r l i e r work, the e f f e c t was a t t r i b u t e d t o t h e production of
d i f f e r e n t degrees of unfolding of proteins. On the same basis, the r e s u l t s
presented here suggest that N a C l increases t h e emulsifying capaxity of
water-soluble proteins by unfolding t h e i r structure, thus extending t h e i r
a b i l i t y t o enclose f a t a o b u l e s in membranes.
Table 5.
Salt s e r i e s
The e f f e c t s of d i f f e r e n t salts on t e emulsifying
capacity of water-soluble proteins-a7
Fat emulsified
d 4.80
M[
ICjCN
146
165
-.
mo3
K
B
r
134
130
KC1
119
KZs04
117
__I_-
rag protein/50 ml, pH values before and a f t e r addition of
s a l t s w e r e 5.52 and 5.12, respectively.
The r e s u l t s shown i n Figure 8 (Slide 13) were obtained on investigating t h e a f f e c t s of varying pH and content of NaCl on the emulsifying
capacity of s a l t - s o l u b l e proteins, The enulsifying capacity of salt-soluble
proteins was not s i g n i f i c a n t l y d i f f e r e n t in 0.3, O.G, and 1 . 2 M solutions of
NaCl, except that pH values approaching pH 5.4, approximately t h e accepted
i s o e l e c t r i c point of t h e salt-soluble proteins. In this pH range, increasing
NaCl produced a s i g n i f i c a n t increase i n the emulsifying capacity, an effect
that can simply be explained as the effect of s a l t in lowering t h e pH a t
which proteins a t t a i n minimLun s o l u b i l i t y .
In Figure 9 (Slide 14), t h e results obtained w i t h meat a r e shown
on comminuting and dispersing samples i n 0.3, 0.6, and 1.0 M NaCl and then
determining t h e i r errmlsifying capacity a t pH values adjusted i n a range
extending from 4.6 t o 8.1. The r e s u l t s apparently r e f l e c t differences i n
the a b i l i t y of the solutions both t o e x t r a c t proteins and t o disperse and
modify t h e i r c h a r a c t e r i s t i c s . Variation of both pH and content of NaCl
strongly influenced emulsifying capacity. An increased concentration of
N a C l increased the emulsifying capacity a t pH values i n the range 5.4 t o
6.0, but had no s i g n i f i c a n t e f f e c t otherwise. I n general, emulsifying
capacity increased markedly with increase in pH. The significance of these
r e s u l t s can be understood by comparing these data with that previously
shown that were obtained wtth water-soluble and salt-soluble proteins. The
curves l a c k maxima a t pH 5.2 a t which pR the water-soluble proteins exhibited
a maximum but have a tendency t o plateau a t pH 5 . 0 where emulsifying capacity
is approximately 100, These r e s u l t s indicate t h a t the apparent contribution
of water-soluble proteins throughout t h e e n t i r e range of pH values in a l l
three concentrations was approximately 100. Also, a comparison of t h e curve
shown here with Figure 6 indicates that t h e emulsifying capacity of meat and
the s a l t - s o l u b l e proteins of meat are genemlly similar i n the region p H 5-6
where increasing MaCl content apparently minimizes t h e e f f e c t of lowering
pH and favorably a f f e c t s emulsifying capacity. Further comparison of these
r e s u l t s with those previously shown indicates that the emulsifying capacity
of meat, but not of t h e salt-soluble proteins, increased a t pH values ranging
from 7 t o 8. The evidence suggests that the e f f e c t of increasing pH was not
75.
exerted by modifying t h e action of dispersed proteins. Rather, a l o g i c a l
explanation i s that increasing a l k a l i n i t y increased extraction of t h e proteins.
To be f u l l y effective, the proteins should be extracted and dispersed. In Table 6 (Slide 15), data a r e given showing the r e s u l t s of a study
of the e f f e c t on t h e emulsifying capacity of meat of varying r a t i o s of water
t o meat added t o cured meat before i t s use i n emulsification.
Table 6
Table 6.
-
The e f f e c t on the emulsifying capacity of meat of
varying content of added water
Ratio b r i y
t o meata
I
_
I-
.
..
&ulsifying capacity,
A
B
mlbJ
C
D
4.0
136
153
196
150
1.0
139
143
199
153
0.5
124
129
189
-
0.25
122
137
170
131
0.125
118
106
163
126
0.0
-
-
-
-
d Volume
of 0.6 M NaCl indicated added t o ground meat containing 5.85:: added NaCl.
'
Four samples, capacity determined on weights equivalent t o
2.5 g meat i n meat-brine mixture adjusted t o 0.28 M NaC1
and 50 m l volume.
In these experiments, aZter t h i s "curing", t h e operation of emulsification
was conducted a t low s a l t concentrations so t h a t proteins, not dissolved o r
f u l l y hydrated during the "curing", would not become dissolved; a t the same
time, conditions which would p r e c i p i t a t e dissolved protein were avoided.
This was obviously done i n an e f f o r t t o d i f f e r e n t i a t e the e f f e c t of d i f f e r ent l e v e l s of water i n curing while eliminating extraction of proteins i n
t h e brine used i n the emulsification process. The results show that emulsifying capacity m.s reduced 15 t o 305 by a d r a s t i c reduction of water content.
The g r e a t e r p a r t of the meat proteins was conditioned by the treatment with
NaCl s o t h a t they were d i s p e r s i b l e i n weak brine and a c t i n g during the
process of emulsification. Obviously the p o t e n t i a l emulsifying capacity i n
meats i s not obtainable when t h e water content of meat emulsions i s res t r i c t e d . On the other hand, reduction of added water apparently e f f e c t s
the i n t e r a c t i o n of NaCl with t h e proteins t o only a moderate extent. The
pH of ordinary meat i s approximately 5.4 t o 6.0, and t h e usual ionic
strength of sausage emulsions is approximately 0.6, o r approximately the
76.
equivalent of 0.6 M ITaCl. Und.er these conditions, the effectiveness of
emulsification is most s e n s i t i v e t o c b n g e i n pH and content of N a C l . The
r e s u l t s indicate t h a t increasing e i t h e r o r both pH and N a C 1 should improve
t h e emulsification o r d i n a r i l y obtained i n preparing emulsion-based meat
products
Some may be i n t e r e s t e d i n the recent work on t h i s project. Ve
found t h a t one i n a u s t r i a l f i r u using our method f o r determining emulsifying
capacity has used t h e r e s u l t s i n computing sausage formulations with the
I B M computer. In general, success was obtained insofar as emulsifying pork
f a t was concerned, but emulsifying beef f a t apparently constitutes a somewhat d i f f e r e n t problem. 'Po handle this problem, we a r e now studying the
emulsification of f a t s containing r e l a t i v e l y large proportions of s o l i d s .
(1) Hansen, L, J. 1960. Etnulsion formation i n f i n e l y comminuted sausage.
Food Technola 14, 565.
(2)
(3)
Ascherson, F. 14. 1925. On t h e physiological u t i l i t y of the f a t s and
a new theory of c e l l formation based on t h e i r cooperation and supported by several new f a c t s . Arch. Anat. Physiol. Lpz. p. 44
(1840) reprinted I n Hatschek, E, "The Foundations of Colloid
C h e m i s t r y , " Wcmillan Co., New York.
Becher, Paul. 1957. "Esrmlsions:
Publishing Corp., New York.
Theory and Practice."
Reinhold
(4) Swift, C. E., Lockett, C., and Fryar, A , J. 1961. Comminuted meat
emulsions
t h e capacity of meats f o r emulsifying f a t . Food
Technol. 15, 468.
-
Y
(5)
L, 1963. Comminuted meat emulslons:
Factors a f f e c t i n g meat proteins a s emulsion s t a b i l i z e r s . Food
Technol. 1 7 , 106.
Swift, C. E , , and Sulzbacher, 1.J.
L
(6)
Adam, Ne= K. 1941. "The Physics and Chemistry of Surfaces," 3rd ed.
Oxfoxd Press, London.
f4R. SAFIU:
papers a r e completed.
Ve w i l l have a discussion session a f t e r t h e next two
The next area that we want t o cover on the m l s i o n Type Sausages
is the Effects of Various Binders on Sausage Zbiulsions, and Nichigan S t a t e
has done considerable work i n t h i s a,rea, and Prof. Bratzler was t o give t h i s
Paper but has been i n t h e hospital the l a s t two o r three weeks. But you a l l
know t h e saying "Old Profs W l l IJever Let You Down", and I believe he contacted AI. Pearson who carted over a l l of the data so t h a t he could write the
Fig. 6 (Slide 10)
FAT EMU L S I F I CATION
Effect on Protein Solutions
WATER-SOLUBLE
SALT-SOLUBLE
BEFORE
Sedimentation of p r o t e i n s in solutions before and after emulsification.
Fig. 7
( S l i d e 11)
FAT EMULSIFICATION WITH
WATER-SOLUBLE PROTEINS
.
-
4
I
5
O.5M Na CI
I
6
I
7
PH
Influence of pH and NaCl on t h e mount of f a t emulsified by water-soluble proteins.
8
Fig. 8
ml
( S l i d e 13)
FAT EMULSIFICATION WITH
SALT-SOLUBLE PROTEINS
180
1.2M No CI
0.6M Na CI
160
140
120
100
6
7
PH
a
Influence of pH and N a C l on the amount of fat emulsified by salt-soluble proteins.
9
80.
E
-
I
m
0
0
0
I
--
I
0
c
00
I
0
.o
c
I
0
.t
c
V
0
z0
0
I
0
m
c
I
0
0
c
81
.
paper there a t the hospital, and we have Jim Price who i s now back a t
Michigan and who will present Professor Bratzler's paper.
MR. JIM PRICE : Thank you, Bob a
Prof. Bratzler, I am sure, regrets that he was unable t o be here
a t the Conference, I know t h a t he wanted very much t o reminiscence and v i s i t
e f e e l conwith h i s friends and colleagues t h a t attend t h i s Conference, W
f i d e n t t h a t Prof. Bratzler w i l l be back a t his desk when we return t o East
Lansing
.
Since I had an occasion t o review t h e formal paper of Dr. Rongey
who did t h i s research work, Prof. Bratzler asked me t o present h i s paper
here t h i s afternoon.
#######If####