Literature Cited
1. Hardenburg, R. E., A. E. Watada, and C. Y. Wang. 1986. The com
mercial storage of fruits, vegetables and florist and nursery stocks U.S.
Dept. Agr. Agr. Hndbk. 66, 130 pp.
2. Ryall, A. L. and W. J. Lipton.
1979. Handling transportation and
storage of fruits and vegetables. Vol. 1, Vegetables and melons. 2nd
ed. AVI Publ. Co., Westport Conn.
3. Fresh Produce Mixer and Loading Guide. TransFresh Corp., P.O.
Box 1788. Salinas, Calif., 93902.
Proc. Fla. State Hort. Soc. 101:207-210. 1988.
QUALITY CHANGES OF CARROT STICKS IN STORAGE
Materials and Methods
Joseph H. Bruemmer
U.S. Citrus &? Subtropical Products Laboratory
600 Avenue S, N.W.
P. 0. Box 1909
Winter Haven, Florida 33883-1909
Abstract. A working hypothesis was developed that senes
cence of carrot sticks can be controlled by regulating
metabolism. The approaches used to test the hypothesis were
low temperature (2°C), modified atmospheres, infusion of
metabolites and cofactors, and growth regulators. Quality
factors were measures of senescence control: taste, color and
texture. Respiratory-CO2 formation and protein depolymerization were also measured. Carrot sticks retained color and
texture in storage at 2°C up to 5 weeks under several mod
ified atmospheres and with infused metabolites. However,
carrot flavor was lost under all treatments. Proteins of the
carrot sticks began to break down after 3 weeks storage. Car
rot tissue gave a weak and slow response to growth regulators
but the response was consistent with response of other plant
tissue to these regulators. The conclusion was drawn that har
vested carrot is physiologically too mature for senescence con
trol and therefore these techniques would be more approp
riately applied to the growing carrot.
Carrot roots grow in a near anaerobic environment be
cause O2-tension of the soil is low. When the root is har
vested it is exposed to the high O2-tension of the atmospfiere which brings about numerous metabolic changes.
Pyruvic acid, for example, contributes about 30% of the
total organic acids in the growing carrot. However, one
day after harvesting pyruvic acid is about 0.1 % of the total
acids and malic and isocitric acids increase to 95% from
about 25% of total acids (11). In addition, enhanced
aerobic respiration promotes depletion of soluble sugars.
When the carrot is processed into carrot sticks the respira
tion rate abruptly but temporarily increases 10-fold (9).
The monosaccharides are metabolized depleting the solu
ble sugars.
A conventional approach to retard respiration and
metabolic rates is to lower temperature of the product and
modify the gaseous atmosphere. A less conventional ap
proach would be to supply metabolites and growth reg
ulators to the product. We have examined these ap
proaches and measured their effect on quality parameters
such as taste, color and texture, and their effect on
metabolic changes such as decarboxylation and hydrolytic
reactions.
The author ackowledges with thanks the technical assistance of Ms.
Holly Hutchens and Ms. Aldys Foerster and the carrots from Charles
Kennedy of Zellwin Farms.
Proc. Fla. State Hort. Soc. 101: 1988.
Carrots (commercial Shamrock type) were obtained in
50-lb bags from Zellwin Farms, Zellwood, FL on the same
day or the day after harvest. They were stored at 2°C until
processed but were used within 3 weeks of storage. The
carrots were sanitized by submerging in cold 1% solution
of sodium hypochlorite for 30 min before they were peeled
mechanically in a Hobart (Model 6430-1) peeler. Carrot
sticks (10 mm2 x 60 mm) were prepared with a Hobart
(Model PD 70) power unit with dicer attachment. Carrot
sticks or cubes (1 cm3) were vacuum infused with solutes
in sterile solutions as described (4). About 300 g of carrot
sticks were packaged in Cryovac E bags (O2 transmission:
4000 cc per m2 at 20°C, 1 atm and 24 hr) or in Cryovac B
bags (O2 transmission: 5 cc per m2 at 20°C, 1 atm and 24
hr). The bags were evacuated and sealed, or flushed and
filled with various gas mixtures and sealed with a Super
Vac, Type GK 115G (Smith Equipment Co., Clifton, NJ).
The packaged carrots were store at 2°C.
Taste preference. A panel of 20 tasters were given 3 or 4
samples of carrot juice to be ranked for preference. The
samples were ranked from 1 to 3 or 4, with 1 for best and
3 or 4 for worse. Ranked sums were used to determine
significance of difference between samples (7, 8). The juice
was prepared by blending carrot sticks with equal volume
of distilled water which was served to the panel at room
temperature.
Color. The color of the carrot juice served to the panel
of tasters was measured in a Minolta Chromameter CR-200
(Minolta Corp., Ramsey, NJ) and expressed as L, lightness
factor, and chromaticity coordinates (a) and (b).
Texture. Texture of the carrot sticks was determined as
resistance to shear using the Kramer shear-compression
cell and the Instron Universal Testing Instrument, Model
1101 as described by Bourne (1). Individual carrot sticks
were measured and the results expressed as Kg per cm2 of
a 5 cm stick.
Protein extraction. Soluble carrot proteins were extracted
from acetone powders of carrot sticks treated with various
regimens of solutes and storage. Acetone powders were
prepared from carrot sticks (400 g) by blending liquid N2
frozen sticks to a powder. Cold acetone (1 L at -90°C) was
added to the carrot powder and stirred for 2 hr in -20°C
room. Then the acetone was decanted and the carrot pow
der was dried in large (25 cm dia) Buchner funnel attached
to water aspirator. The mat of powder was finally rinsed
with 200 ml of -90°C ethyl ether and vacuum dried in
desiccator for 24 hr at 25° with desiccant. The dry sample
was ground to a fine powder and stored at —90°C.
Proteins were extracted from the dried acetone powder
with buffered solution at pH 8.1 containing 0.05 M Tris
HC1, 0.001 M dithiothreitol, 0.005 M EDTA, 20% polyclar
207
AT and phenylmethylsulfonyl fluoride (50 g per ml of
buffer dissolved in ETOH). The acetone powder was
added to 4°C buffer at 5% w/v and stirred for 4 hr at 4°C.
After centrifuging at 10,000 x g for 30 min the supernat
ant was decanted from the extraction mixture and proteins
precipitated by 80% saturated (NH4)2 SO4. The precipita
tion occurred over 6 hrs stirring at 4°C, after which the
precipitate was recovered by centrifugation at 10,000 x g
for 20 min. The (NH4)2SO4 solution was decanted and the
residue was dissolved in 20 ml 0.1 M PO4 buffer pH 7.2.
The protein solution was again centrifuged at 10,000 x g
for 20 min and then the decanted protein solution was
dialyzed against 0.01 M PO4 buffer; pH 7.2, 12 to 18 hrs
at 4°C. The dialyzed solution was again centrifuged at
10,000 x g for 20 min and the supernatant recovered and
stored frozen at -90°C.
Electrophoresis and densitometry. Protein content of the
extracts was determined by the method of Bradford (2).
SDS-denatured proteins were separated on gradient and
homogeneous polyacrylamide gels using the Phastgel Sys
tem (Pharmacia, Piscatany, NJ). Gels were stained with
Coomassie or silver dyes for visualization. Density of bands
on the tracts were compared and related to treatments with
an Ultra-Scan XL Laser densitometer with computer as
sisted software (Pharmacia, Piscatanay, NJ).
Respiratory CO2 . Carrot cubes (1 cm3) were sterilized by
placing them in 70% ethanol at 25°C for 30 sec and then
rinsing them in sterile distilled water and then in 0.3 M
mannitol before planting them in semi-solid media (3, 10)
containing 0.1 M potassium pyruvate and various growth
regulators to be tested. All manipulations were carried out
in a sterile laminar flow hood. The flasks (50 ml erlenmeyer) containing 15 ml of the semi-solid media and four
carrot cubes were capped with rubber sleeve stoppers. CO2
was sampled from flasks by withdrawing 5 ml gas with 10
ml syringe through the rubber sleeve stopper. The sample
loop (0.5 ml) of the gas chromatograph (Perkin Elmer
8500) was flushed with the 5 ml gas sample and then the
gas was valved on to the Porapak-S and molecular sieve
columns which separated the CO2 from other gases with
Table 1. Preference scores for stored carrot sticks.7
He carrier. CO2 was detected with a hot wire detector.
CO2 content of the gas sample was calculated from the %
of CO2 in the flask and expressed as ml of CO2 formed.
Results and Discussion
Taste preference. In the first experiment (Table 1) the
ranked sums for the shrink pack carrot sticks were signif
icantly higher than other treatments during the first week.
Over the 25 day experiment 6 of the 12 ranked sums for
the shrink pack were significantly higher than other treat
ments. Thus, the panel preferred carrot sticks from the
other treatments to those from the shrink pack. However
both air storage and 8% CO2 plus 4% O2 in N2 elevated
the preference scores over the fresh cut samples. Gas trans
mission properties of the bags did not consistently influ
ence the preference ranking for any of the gas treatments.
Freshly cut sticks from stored whole carrots were preferred
by the taste panel throughout the experiment. Thus, the
presence of air, low O2 with high CO2, or low pressure
atmosphere did not modify the damage of storage to carrot
flavor.
The preference scores from experiment 2 (Table 2)
also illustrate that freshly cut sticks from stored whole car
rots are best liked and that the atmosphere cannot com
pensate for the adverse flavor effects of storage. In this
experiment the atmosphere of 2.5% CO2 and 2.5% O2
partially modified the flavor damage that resulted from
storage in the carrot sticks because only one score at 16
days was significantly worse than other test samples. The
CO2 concentration in the modified atmosphere is critical
in storage of many vegetables (6). Concentrations higher
that 3% CO2 in gas mixtures increased respiration and
decay in stored whole carrots (14, 17).
Vacuum infusion of glucose, sodium pyruvate and cal
cium chloride into carrot sticks significantly decreased taste
preference after storage (Experiment 3; Table 3). These
compounds improved texture and color of carrot sticks in
storage (4). Gassing the infused carrots with 8% CO2 plus
4% O2 in N2 slightly improved the preference score com
pared to gassing with air after 28 and 34 days. Fresh cut
carrot sticks and shrink packed sticks were preferred by
the panel to the infused sticks. Results of these experimeats
Days in
Gas
Fresh
Shrink
storage
trans.
cut
pack
Air
8.0% CO2
4.0% O2
in N2
High
37
62
56
45
Low
36
57
57
50
High
24
64
61
51
Low
22
69
53
56
High
29
43
60
68
Low
37
51
47
65
3
7
8
12
17
25
High
20
69
56
55
Low
32
68
47
53
High
23
70
54
53
Low
30
53
55
62
High
42
28
56
50
47
63
55
Low
59
zPanel of 20 tasters ranked 4 samples: 1 (best, liked), 2 (next best), 3 (less
P liked), and 4 (east liked). Significant differences between ranked sums
(P < 0.01):62 or higher, 38 or lower (ref. 7, 8) are underscored.
208
en:ipiiasize
me
neea
co
laenuiy
icne
reactions mat
adversely affect flavor during storage.
Ranked sums after storage
Table 2. Preference scores fbr stored carrot sticks.
Ranked sums after storage2
2.5% CO2
2.5% O2
in N2
Days in
Gas
Fresh
storage
trans.
cut
Air
High
31
48
41
Low
36
48
38
43
46
9
12
15
High
31
Low
26
High
33
30
43
35
47
High
26
54
40
Low
29
36
55
Low
16
43
55
"Panel of 20 tasters ranked 3 samples: 1 (best liked), 2 (next best), and 3
(least liked). Significant differences between ranked sums (P < 0.01):48
or higher, 32 or lower (ref. 7, 8) are underscored.
Proc. Fla. State Hort. Soc. 101: 1988.
Table 3. Preference scores for stored carrot sticks.
Ranked sums after storage2
2% glu,
0.01% pyr&
0.02% CaCl2y
8% CO2,
4%O2
Days in
Gas
Fresh
Shrink
storage
trans.
cut
pack
Air
in N2
7
3
28
34
High
29
40
64
64
Low
32
41
63
64
High
24
57
64
55
Low
25
48
62
65
High
33
50
55
42
38
75
Low
61
46
High
37
32
73
70
49
53
Low
41
45
zPanel of 20 tasters ranked 4 samples: 1 (best liked), 2 (next best), 3 (less
liked), and 4 (least liked). Significant differences between ranked sums
(P < 0.01): 62 or higher, 38 or lower (ref. 7, 8) are underscored.
yCarrot sticks were vacuum infused with a solution containing 2% glucose,
0.01% pyruvate and 0.02% calcium chloride before being bagged and
gassed with air or a mixture of 8% CO2 and 4% O2 in N2.
Texture. The shear resistance of all the stored carrot
sticks in experiments 1, 2, and 3 differed only slightly from
the freshly cut sticks from stored whole carrots. The stored
and fresh carrots ranged between 58 and 80 kg/cm2 for 5
cm stick. Even the carrot sticks stored for 25 and 34 days
were not significantly different from the fresh cut sticks.
The effective barrier to moisture loss that film provided
prevented gross changes in the texture of the carrot sticks
during storage. (Data are not shown).
Color. No significant difference was detected between
color of fresh cut and stored carrot sticks as determined
by the L, a, b system of measurement. L ranged from 58
to 69; a from 24 to 32 and b from 48 to 64. Measurements
of color were made on juice so that variation in color of
the individual carrot stick would not contribute to the read
ings. (Data are not shown).
Growth regulators. Respiratory CO2 formation is an
index of general metabolism. Agents that affect CO2 for
mation are potential regulators for controlling senescence.
Several phytohormones were tested for regulator activity
in the carrot. CO2 production by carrot tissue was not af
fected by 1(H, 10-3 or 10"2 M Gibberellic acid (GA) (Table
4). Experimental variation between flasks in CO2 forma
tion was large as noted by the large SD for the various
means. Benzyladenine (BA) and abscisic acid (AA) at 10~2
M suppressed CO2 formation but the lower concentrations
of these growth regulators were not effective inhibitors.
The 2,4-dichlorophenoxyacetic acid (2,4-D) concentration
of 10~2 M stimulated respiration after four and six days.
Failure to get a response to the lower, more physiological
levels of growth regulators may be explained by di
minished respiratory CO2 production by the carrot tissue
because of handling in preparation for the culture
medium. Also transport of the growth regulators may be
impeded in the gelled medium. Vendrell (16) found that
vacuum infiltration was more effective than dipping in ri
pening response to GA. He also observed no effect of GA
on CO2 formation. BA was also observed to decrease respi
ration in broccoli (5) and in apples (13). Vendrell (15) re
ported that 2,4-D increased respiration in bananas when
clipped in 10"2 and 10~3 M solutions. Thus the response of
carrot tissue to the growth regulators is consistent with
reports on other vegetable tissue.
Protein changes in storage. During storage of vegetables
the protein level falls with a concomitant increase in lower
molecular weight polypeptides and free amino acids. Most
of the postharvest transformations in amino acids and pro
teins of vegetables are regulated by enzymes within the
storage organs. In ripening and senescing fruits synthesis
of hydrolytic enzymes have been shown to increase (12).
Comparison of Phastgels of SDS-denatured proteins
and polypeptides separated electrophoretically on gradient
polyacrylamide from extracts of carrot sticks stored for 1,
2 and 3 weeks and freshly cut carrot sticks indicated differ
ences in position of the bands (Table 5). As the carrot
sticks aged in 2°C storage from 1 to 3 wks the position of
Table 4. Response of respiring carrot tissue to growth regulators.
CO2 production ;cc/flaskz
Growth regulator
Gibberellic acid
X10-3M
2,4 Dichlorophenoxy-
acetic acid
4 days
6 days
0
0.30 ± 12
0.35 ±0.11
0.78 ± 0.33
0.61 ± 0.27
1.0
0.38 ± 0.26
0.32 ±0.11
0.74 ± 0.34
1.20 ±0.31
0
0.82 ± 0.20
1.42 ±0.50
0.1
0.60 ± 0.30
1.00 ±0.63
1.0
0.78 ±0.28
0.49 ±0.22
075 ± 0.44
10.0
Abscisic acid
2 days
0.1
10.0
Benzyladenine
lday
0
0.1
1.0
1.37 ± 0.77
1.01 ± 0.36
0.94 ± 0.61
1.24 ± 0.50
1.20 ± 0.87
0.74 ± 0.23
0.46 ±0.16
0.91 ± 0.25
10.1
0.93 ± 0.37
0.53 ± 0.26
0
0.81 ± 0.28
0.1
0.95 ±0.11
1.00 ± 0.01
1.0
0.71 ± 0.32
10.0
1.65 ± 0.48
0.82 ± 0.39
1.89 ±0.53
zMean ± SD of 4 flasks. Values underscored are significantly different (P < 0.05) from untreated value for that treated series, as determined by
Tukey's Studentized Range (HSD).
Proc. Fla. State Hort. Soc. 101: 1988.
209
Table 5. Protein bands from SDS-PAGE of carrot extracts.z
Position of band (mm)
1st
Fresh
week
2nd
week
13.00
12.84
13.36
15.36
15.64
13.96
16.44
15.28
17.76
17.40
17.80
16.72
17.72
18.68
18.96
21.80
22.84
24.16
Peak height (AU)y
3rd
week
1st
Fresh
week
0.33
0.26
0.41
0.33
0.30
0.48
0.38
0.42
0.49
0.53
21.84
19.12
22.20
23.48
23.04
25.72
26.04
0.62
25.40
26.48
25.72
26.08
27.36
27.04
27.88
29.84
26.92
30.12
30.72
30.56
32.80
33.20
31.92
30.12
31.08
33.24
2nd
week
0.31
17.36
18.32
20.36
33.76
24.04
30.44
Conclusion
0.57
0.52
0.51
0.53
0.56
0.58
0.50
0.58
0.61
0.59
0.62
0.79
0.78
0.53
0.62
0.53
0.55
0.76
0.71
0.77
0.57
0.57
0.57
0.59
0.58
0.64
3rd
week
0.25
0.38
0.46
0.55
0.57
0.54
0.62
0.53
0.44
0.75
0.51
zGradient gels: 8-25% polyacrylamide starting from stacking gel. Values
are densitometer readings with peak heights normalized to highest peak.
yAU, Absorbance Units.
The harvested carrot is a senescent tissue on the basis
of the weak and slow response to the growth regulators.
None of the experimental approaches attempted arrested
the senescent state as the flavor was rapidly lost and the
proteins began to depolymerize in storage. Since the har
vested carrot is physiologically too mature for senescence
control, these techniques would be more appropriately
applied to the growing plant.
Literature Cited
1. Bourne, M. C. 1968. Texture profile of ripening pears. J. Food Sci.
33:223-223.
2. Bradford, M. M. 1976. A rapid method for the quantitation of microgram quantities of protein. Anal. Biochem. 72:248-252.
3. Bruemmer, J. H. and J. M. White. 1986. Use of phytoalexin produc
tion in carrot cell cultures to evaluate leaf blight susceptibility. Proc.
Fla. State Hort. Soc. 99:156-157.
4. Bruemmer, J. H. 1987. Stability of prepared carrot sticks in storage.
Proc. Fla. State Hort. Soc. 100:36-38.
5. Dedolph, R. R., S. H. Wittwer, V. Tuli, and D. Gilbart. 1962. Effect
of N6-benzylaminopurine on respiration and storage behavoir of
broccoli (Brassica oleracea var. Italica). Plant Physiol. 37:509-512.
6. Herner, R. C. 1987. High CO2 effects on plant organs, p. 239-253.
In: J. Weichmann (ed.). Postharvest Physiology of Vegetables. Marcel
Dekker, New York.
the bands increased in distance from the stacking gel and
toward the 25% gel. This shifting in position indicates
change from high molecular weight proteins in fresh car
rots toward lower molecular weight polypeptides in stored
carrots. Peak heights of the bands were normalized in each
tract to the highest band peak in that tract. The highest
band peaks were positioned at 29.84 mm and 30.44 mm.
At the lower end of the tracts bands were registered at
13.00 and 12.84 for fresh and 1 wk stored carrot sticks but
not below 15.64 mm for 2 wks stored sticks or below 17.36
mm for the 3 wk stored sticks. The pattern of band posi
tions and peak heights for fresh and stored carrot sticks
suggest that proteins are depolymerizing to lower molecu
lar weight polypeptides in carrot sticks during 2°C storage.
We have also examined the separation of SDS-denatured
protein from the carrot extracts on 7.5, 12.5, and 20%
homogeneous polyacrylamide gels. For homogeneous gels,
the intensity and position of the high molecular weight
proteins showed the same inverse relationship with storage
time (data not shown). We are in the process of estimating
the molecular weight of the protein bands and locating the
proteases and peptidases on the gels to quantitate the
changes of the enzymes in storage.
210
7. Kahan, G., D. Cooper, A. Papavasiliou, and A. Kramer. 1973. Ex
panded tables for determining significance of difference for ranked
data. Food Tech. 27:61-68.
8. Kramer, A. 1960. A rapid method for determining significance of
differences from ranked sums. Food Tech. 14:578-581.
9. Laties, G. G. 1978. p. 421-466. In: G. Kahl (ed.). Biochemistry of
Wounded Plant Storage Tissues, de Gruyter, Berlin.
10. Murashige, T. and F. Skoog. 1962. A revised medium for rapid
growth and bioassay with tobacco tissue culture. Physiol. Plant.
15:473-497.
11. Phan, C.-T. 1987. Biochemical andd physiological changes during
the harvest period, p. 9-22. In: J. Weichmann (ed.). Postharvest of
Vegetables. Marcel Dekker, New York.
12. Sacher, J. A. 1973. Senescence and postharvest physiology. Ann. Rev.
Plant Physiol. 24:197-223.
13. Smock, R. M., D. Martin, and D. H. S. Padfield. 1962. Effect of
N6-benzyladenine on the respiration and keeping quality of apples.
Proc. Am. Soc. Hort. Sci. 81:51-56.
14. Stoll, K. 1974. Storage of vegetables in modified atmospheres. Acta.
Hort. 38:13-20.
15. Vendrell, M. 1970. Relationship between internal distribution of
exogenous auxins and accelerated ripening of banana fruit. Aust. J.
Biol. Sci. 23:1133-1142.
16. Vendrell, M. 1970. Acceleration and delay of ripening in banana
fruit tissue by gibberellic acid. Aust. J. Biol. Sci. 23:553-559.
17. Weichmann, J. 1977. Physiological response of root crops to control
led atmosphere. Proc. 2nd National Controlled Atmosphere Re
search Conf., Mich. State Univ. Hort. Rept. 28:122-125.
Proc. Fla. State Hort. Soc. 101: 1988.