FLORIDA
198
STATE
HORTICULTURAL
SOCIETY,
1965
CITRUS FRUIT RESPIRATION1
data were also possible with bulk samples since
H. M. Vines2
G. J. Edwards and
decaying, dropped or otherwise, mishandled fruit
W. Grierson3
could be unknowingly included in a sample.
Such
Abstract
An apparatus was devised to facilitate meas
urement of respiration rates of single fruits
using automatic switching and instrumental
recording. Fruits studied were 'Valencia' orange,
'Bearss' lemon, and 'Murcott' tangor. Respira
tion rates are presented as mG, CO2/kg/hr and
the effect of various factors expressed also in
terms of respiration rate as a percentage of that
of the control sample. Effect of various factors
were: rapid air cooling, 115%; hydrocooling, 120
to 130%; dropping 24 inches to a hard surface,
140%; idem 48 inches, 190%; 10 pounds steady
pressure for 30 seconds, 120%; idem 20 lbs.
165%; ethylene at 50 ppm, 400%; subnormal
oxygen (6 and 10%), 40%.
Introduction
The external manifestations of fruit
tion are the intake of 02, the evolution
and heat. By measurement of either
exchange, one can determine the rate of
tion which reflects the physiological
respira
of CO2,
gaseous
respira
effects of
various storage and handling practices.
Because
these
gaseous
exchange
rates
study
errors
by
have
been
investigating
handling practices on
eliminated
the
effect
of
in
this
various
the respiration rates
of
individual fruits.
Experimental Methods
Carbon
dioxide in
a
continuous air stream
was measured with a Model 215 Beckman infra
red nondispersion CO2 analyzer, designed to
record CO2 at 0 to 600 ppm.
passed
over single
enclosed
This air stream
fruits. To utilize
the equipment efficiently, a switching apparatus
was designed to allow the air stream from each
of the 12 sample fruit to be analyzed in sequence
(Figure 1). This instrument was fabricated to
our specifications by the Instrument Development
Company, Riverside, California.
Atmospheric
air was supplied by a pump and regulated with
flowmeters and manometers to a rate of 30 or
60 ml/min. The time cycle frequency was adjust
able so that CO2 readings could be made on
each of the 12 fruit at intervals that could be
varied from 1 to 6 hours. Analyses were record
ed on a Heathkit recorder in microamps (^a)
which were converted to ppm CO2 by reference
are
relatively small, especially in citrus, the methods
previously available for analyses of gases were
cumbersome or insensitive at very low concentra
tions of the gas being analysed. Because of this,
multiple fruit samples have been commonly used
for respiration studies. Such an approach has
been avoided here as it assumes that all fruit
within the sample behave the same, which is not
necessarily true.
Erroneous interpretations of
to a standard curve.
All respiration
data are reported as
milli
grams CO2 per kilogram fruit per hour (mg
CO2/kg/hr) according to the following equation:
ppm CO2 x air flow (ml/hr) x C.F.* =
1,000,000 x fruit weight (kg)
mg CO2/kg/hr
* Conversion factor for ml CO2 to mg CO2—
See Table 1.
Ethylene analyses were made on an Aero
600-B flame ionization gas
graph Hi-Fi Model
Florida Agricultural Experiment Stations Journal Series
No
2235.
lCooperative research by the Florida Citrus Commission
and the Florida Citrus Experiment Station.
2Associate Biochemist, Florida Citrus Commission.
3Assistant in Chemistry and Horticulturist, University of
Florida Citrus Experiment Station, Lake Alfred.
chromatograph equipped with a Model 328 bal
listic temperature programer.
Tank -hydrogen
and oxygen were used for the flame with nitro
gen as the carrier gas.
VINES,
EDWARDS,
GRIERSON—FRUIT
RESPIRATION
199
(-►OUT
Figure 1.—Flow diagram for respiration lines. A - Trap for moisture condensate; B - Air pump Neptune Dyna Model 3;
C - Bleed off hose clamp; D - Inlet manifold; E - Sample chamber; F - Manometer; G - Capillary; H - Flow control
valve on Instruments Development Co., Model V-12-C automatic sampling: system; I - Selector cam in sampling system;
J - Exit closing cam in sampling system; K - Outlet manifold ; L - Beckman infrared analyzer Model IR-215 sample cell;
M - Flowmeter; N - Heath Kit Servo Recorder Model EUW 20A; O - Sage Instrument Syringe pump Model 255-3.
The column was
%" x 35%" stainless steel
packed with 4.3 grams of Fisher's A-540, 80 to
200 mesh alumina.
The
instrument gas
flows
were standardized as follows: hydrogen flow at
the burner tip 34 ml/min, oxygen 600 ml/min,
and nitrogen carrier gas
10.3 ml/min.
Under
these conditions, the retention time was 1 min
ute.
for
The column was heated to 350 to 400° C
3 days
before use, and the
injection and
column temperatures were both 50° C.
The in
put impedance on the electrometer was
at 109
adjustable to allow any desired concentration of
ethylene.
Each
experimental
fruit was
weighed
and
placed in its gas tight container, and the con
trolled air flow was directed over the fruit and
into the CO2 analyzer.
All treatments were replicated from 3 to 6
times in each run, CO2 readings being made on
each fruit 4 times every 24 hours. Thus, each
point on the graphs shown in this study repre
sents an average of 12 or 24 analyses per day.
and the output sensitivity was at 1 X.
Standards were made up with C.P. ethylene
ranging from 5,000 ppm to 0.5 ppb and plotted
on the basis of peak height.
syringes
(1
ml)
were
used
Hamilton gas tight
for
sampling and
injections.
Table 1.
Conversion of CO2
Temperature
°C
(ml)
to CO2
Conversion Factor
°F
mg C02/ml CO2
0
32
1.977
ethylone
5
41
1.941
10
50
into the controlled air stream flowing over the
1.901"
15
59
1.879
20
68
1.870
25
77
1.811
30
86
1.781
35
95
1.752
Treatments
tions were
fruit.
of
specific
ethylene
concentra
obtained by injecting C.P.
To achieve this, a Sage syringe infusion
pump Model 255, capable of delivering as low a
rate as 0.42 ml/24 hours, was used. Both ethylene
injection
rates
and
air
stream
volumes
were
(mg).
FLORIDA
200
STATE
Fruit varieties used were
oranges, 'Bearss* lemons, and
HORTICULTURAL
'Valencia'
'Murcott';
late
the
latter a natural hybrid believed to be a tangor
(orange x
tangerine hybrid).
In repeating
a
of 140%
SOCIETY,
1965
and a 48-inch drop resulted in
190%
as compared to the control as 100%.
During
harvesting,
fruit in many ways:
pressure
is
applied
to
on bottom-fruit in a box
set of experiments, fruit from a different source
or bulk bin; on top-fruit in over-filled boxes by
or picking was used.
the succeeding box on top; pickers force their
bags
against the ladder, etc.
The
exact force
applied and time of applied pressure is open to
Results
question.
The apparatus, having been built and tested,
A pressure of 10 and 20 pounds between 2
was used in preliminary studies to check the
effect of various factors generally accepted as
liable to affect the respiration rate of fruits.
None of these had ever been reported upon for
Florida-grown citrus. For some of the varieties
used, no respiration data is known from any
flat surfaces for 30 seconds caused an increase
in respiration rate as can be seen in Figure 3.
The
fact that
age.
ently
source.
the
20-pound
The
10-pound pressure
exhausted
the
An increase in respiration rate of single
lemons or oranges which had become naturally
infected with Penicillium digitatum occurred 24
to 48 hours before decay symptoms could be
detected. The respiration rate increased from
an average about 12 mg CO2/kg/hr to approxi
mately 40 within the 1- to 2-day period before
the infection could be seen. This acceleration
of respiration rate continued to above 100 mg
CO2/kg/hr as the infection spread throughout
treatment
intercellular
causing any cell breakage,
Fungal Attack
pressure
treated
fruit did not return to normal within 7 days is
interpreted as indicative of internal fruit dam
and
air
the
appar
without
apparent
lower than normal respiration rate after 2 days
was an equilibration adjustment of the exhausted
intercellular spaces.
Ethylene Treatment
Ethylene has been used for many years
to
speed degreening of citrus (2) and is known to
200
the fruit.
Effects
natalensis
of
stem-end
and Phomposis
rot
fungi
citri)
(Diplodia
differed from
that due to P. digitatum in that the increase in
respiration rate after visible infections did not
attain as high a rate.
Effect of Refrigeration
Rapid cooling of 'Valencia* and 'Murcott'
oranges with a cold air blast was compared with
hydrocooling, both to a mass average temperature
of 45° F. The comparison was repeated 3 times.
In each case, the cooled fruit were allowed to
warm to a constant 60° F, at which temperature
respiration rates were measured. The air-cooled
fruit had a respiration rate of 115% of that of
control fruit which were allowed to equilibrate
at 60° F after harvest, and the hydrocooled
fruit had a rate of 120 to 130% of the control
CONTROL
fruit.
Rough Handling
Eaks (1) has shown that dropping California
'Valencia' and navel oranges on a hard surface
This was
caused an increase in respiration rate.
confirmed with Florida Valencia' oranges as can
be seen
in
Figure 2.
A
24-inch
drop
onto
hard smooth surface caused a respiration
a
rate
71
6.1
6.2
7.7
79
3
4
5
76 7.6
TIME-DAYS
Figure 2.—The respiration rate of 'Valencia' oranges at
60 o F as affected by dropping 24 and 48 inches to a hard
surface. (Numbers in the graph are respiration rate ex
pressed as mg CO2/kg/hr.)
VINES,
EDWARDS,
GRIERSON—FRUIT
Low
201
Oxygen
Controlled
170
o
RESPIRATION
atmosphere
storage
(in
which
oxygen is reduced below the normal 21%) has
been reported to extend storage life and delay
color development, and experiments on this tech
nique have been reported elsewhere (3). The
controlled atmosphere apparatus was intercon
nected to the equipment used in this study mak
ing possible the measurement of respiration of
lemons ('Bearss' strain of 'Sicilian') at reduced
levels of O2. A reduction in respiration rate
occurred at all 02 levels below normal (Figure
5). Both 6% and 10% 02 reduced the respiration
-20 POUNDS
|90
• 9.8
A8.0
IK
79
xo7l
loop
67 6.6\
S.3
7.6
78 7.6
rate to 40% of the control.
Summary
£3<
*♦_* XA
*—
CONTROL \ ,-O>
1. Before any visible symptoms are appar
ent, there is a pronounced increase in the res
piration rate of Bearss' lemons and 'Valencia'
oranges infected with fungi, particularly Pencillium digitatum.
10 POUNDS
_j_
J_
70
2
I
3
4
TIME-DAYS
Figure 3.—The respiration rate of 'Valencia' oranges at
60 o F as affected by mechanical pressure applied for 30
seconds. (Numbers in the graph are respiration rate ex
pressed as mg CO2/kg/hr.)
increase respiration rate as well as decay from
stem-end rot.
A thorough study has never been
made on the relationships between: concentration
of ethylene, temperature,
degreening rate, and
respiration rate.
The concentration of ethylene
for
commercial
degreening
1:30,000 (33 ppm)
is
although
recommended
approximately
1
to
10
ppm
of
ethylene have some degreening effect on citrus
(2).
Ethylene
adsorbed
is
apparently
by the fruit and
absorbed
and/or
containers
making
exact concentrations difficult to confirm.
Ethy
lene injected into the air stream over the fruit
to obtain a concentration of 10 to 50 ppm could
not be detected in the exhaust air although the
fruit degreened satisfactorily.
The increase in
24
hours
exposure
respiration
to
ethylene is shown in
rate
caused by
approximately
Figure
4.
The
50
ppm
increase
reached a peak of more than 400% on the sec
ond
day.
Thereafter,
the
respiration
clined but did not return to normal
control)
within
7 days.
rate
(100%
de
of
TIME-DAYS
Figure 4.—The respiration rate of 'Valencia' oranges at
60o F as affected by 50 ppm of ethylene for a 24-hour period.
(Numbers in the graph are respiration rate expressed as
mg CO2/kg/hr.)
FLORIDA
202
STATE
HORTICULTURAL
2.
O|00
12.5 15.6
14.5 115.0 15.0 16.0
SOCIETY,
1965
Rapid cooling by air or water may con
tribute
to
increased
respiration
in
'Valencia'
oranges and 'Murcott' tangors.
3. Dropping
'Valencia*
oranges
to
a
hard
surface or subjecting them to a pressure of 20
pounds for 30 seconds
respiration rate.
4.
caused
an
increase in
Exposure of 'Valencia' oranges to 50 ppm
of ethylene for a 24-hour period caused an in
crease in the respiration rate above the control
fruit. This higher rate continued during the
7
days under study.
5.
Oxygen concentrations below normal re
duced the respiration rate of 'Bearss' lemons.
REFERENCES
1.
Eaks I. L.
1961. Techniques to evaluate injury to
citrus fruit from handling practices. Proc. Am. Soc. Hort.
Sci. 78: 190-196.
2.
Grierson, W., and W. F. Newhall. 1960. Degreening
of Florida citrus fruits. Fla. Agr. Expt. Bull. 620.
3.
Grierson, W., H. M. Vines, M. F. Oberbacher, S. V.
Ting, and G. J. Edwards.
1965.
Controlled atmosphere
storage of Florida and California lemons. Submitted Proc.
Am. Soc. Hort. Sci.
Figure 5.—The respiration rate of 'Bearss' lemons at 60°
F as affected by subnormal oxygen levels. (Numbers in the
graph are respiration rate expressed as mg CO2/kg/hr).
PREVENTION OF FOAM IN JUICE FROM RECONSTITUTED
CITRUS POWDERS1
R.
E.
Berry,
O.
and on
W. Bissett and
Foam-mat drying enables the dehydration of
heat sensitive foods under relatively mild
con
ditions
The
without
undue
quality
change.
process has been under study for some time and
several commercial operations have developed.
The process has evolved in several basic forms
including
drying
on
a
Teflon-coated
an endless stainless
steel
belt.
Lemon
powders are presently being produced by a com
Charles J. Wagner, Jr.2
fiberglass
belt (3), on perforated stainless steel trays (5),
lCooperative research of the Florida Citrus Commission,
the Western Utilization Research and Development Division
and Southern Utilization Research and Development Division,
Agricultural Research Service, U. S. Department of Agri
mercial concern on a perforated tray or "crater"
type dryer
(7), and -.another company has pro
duced quite
a
number of fruit
and vegetable
products on an endless stainless steel belt dryer
which uses high belt speed and very short drying
time
(1).
Basically,
the process
may
be
de
scribed as follows: a fruit or vegetable juice is
mixed with a foaming or foam-stabilizing agent
and a stiff table foam is produced, this foam is
introduced
onto
one
of the surfaces
described
above and passed into a hot air drying chamber.
Many types of agents are used for production
culture.
of foams and each of them offers certain distinct
Haven, Florida.
advantages.
2TJ. S. Fruit and Vegetable Products Laboratory, Winter
3 One of the laboratories of the Southern Utilization Re
search and Development Division, Agricultural Research
Service, U. S. Department of Agriculture.
References to brand names do not indicate endorsement.
One most often used is the mono-
glyceride, or
fatty-ester
the capacity
to
produce
type.
This agent has
extremely
fine
foams