SHOWALTER: WATERMELON COLOR
Am. Soc. Hort. Sci. 66: 146-154. (Various commercial fungicidal waxes are now available.)
13. Oberbacher, M. F., W. Grierson and E. J. Deszyck,
1960. Florida lemons for the fresh fruit market. Presented
to Am. Soc. Hort. Sci., August, 1960.
14. Oberbacher, M. F. and W. Grierson. Handling meth
ods for fresh Florida lemons: Low temperature studies on
the Sicilian variety. Presented to the Florida State Hort.
Soo, October, 1960.
15. Rose, D. H., C. Brooks, C. O. Bradley and J. R.
Winston, 1943. Market diseases of fruits and vegetables:
Citrus and other subtropical fruits. U.S.D.A. Misc. Pub. 498.
289
16.
Rose, D. H., H. T. Cook and W. H. Redit, 1951.
Harvesting, handling and transportation of citrus fruits.
U.S.D.A. Bibl. Bui. No. 13.
17. Wenzel,
F.W., R. W. Olsen, R. W. Barron, R. L.
Huggart, Roger Patrick and E. C. Hill, 1958. Finding the
best lemon for Florida —a report of progress II. Use of
Florida lemons in frozen concentrate for lemonade. Proc.
Fla. State Hort. Soc. 71: 129-132.
18. Winston, J. R. and
control in Florida lemons.
31-37.
G. A. Meckstroth, 1943. Decay
Proc. Fla. State Hort. Soc. 56:
WATERMELON COLOR AS AFFECTED BY MATURITY
AND STORAGE
Experimental Procedure
R. K. Showalter
Florida Agricultural Experiment Station
Gainesville
Internal color of watermelons is one of
the most important factors in determining
grade and market quality. Zechmeister and
Polgar (6) have reported that the pigments
in watermelon are carotene and lycopene in
a ratio of 1:12. Many studies have shown
a post-harvest increase in carotenoid pigments
in fruits and vegetables. In a previous study
(4) of post-harvest changes in watermelons
it was observed that a redder color developed
during storage.
Vogele (5) has shown that temperature is
an important factor influencing lycopene
formation in tomatoes but not in watermelons.
Temperatures higher than 86 °F inhibited
lycopene formation in tomatoes, but tempera
tures as high as 99° did not inhibit the forma
tion of lycopene in watermelons. According
to Kramer and Haut (3) the yellow pigment
in stored peaches increased at 88° and de
creased at 60°. Ezell and Wilcox (1) re
ported that storage temperature was an im
portant factor influencing carotenoid pigment
changes in sweet potatoes. Pigment content
increased at 60° and 70°, remained unchanged
at 55°, and decreased at 50 &.
The purpose of this paper is to present
information on the effects of storage tempera
ture and duration upon the internal color
and pigment content of watermelons. An ob
jective procedure was also desired which
would measure the observed color differences.
Physical measurements of reflectance and
chemical analyses of pigments were made.
Florida Agricultural
No. 1179.
Experiment
Station
Journal
Series.
Measuring the average color or pigment
of watermelon flesh was difficult because the
area was large and the color was not uniform
throughout the melon. A % inch cross-section
slice was cut from the sample melons about
midway between the two ends. The edible
portion was cut from the rind, deseeded, and
blended for Vk minutes to a uniform slurry.
Duplicate 4 gram samples of the slurry were
extracted with an ethyl alcohol-benzene mix
ture (5:3) by shaking in an Erlenmeyer flask
for 10 minutes. The solution was filtered,
made up to 100 ml, and the percent transmittance was measured with a Spectronic 20
Colorimeter at 475 millimicrons using the
alcohol-benzene mixture as the reference sol
vent.
Reflectance measurements were made on
a cross-section of the melon adjacent to the
slice which was removed for pigment analysis.
Eight to ten seedless areas, % inch in diameter,
on the cut surface of each melon were meas
ured with a Photovolt Reflection Meter, Model
610, equipped with tristimulus filters. The
three readings at each location were made
immediately after cutting the melon to avoid
changes in color. The reflection meter was
standardized with a light red ceramic tile
which was calibrated by a G.E. recording
spectrophotometer as follows: green 36.9,
amber 50.2, and blue 32.3.
Sampling
This study was conducted during the 1959
and 1960 seasons. Three lots of Charleston
Gray watermelons were obtained from com
mercial growers during 1959. In lot 1, the pig
ment content of melons stored 2 weeks at
72°-92°F was compared with that at harvest.
Melons from lots 2 and 3 were stored at 50°
FLORIDA STATE HORTICULTURAL SOCIETY, 1960
290
When the melons were selected in the field
an attempt was made to take only those with
pale red or good red flesh and to exclude all
immature and over-mature melons. A number
of melons in each field were cut before se
lecting those for the storage tests. In one lot
(No. 3, 1960) the same melons were sampled
at harvest and after 1 and 2 weeks in storage
to make certain that differences in color after
storage were not due to differences at harvest.
One half of each melon was stored at 50°
and 72°-92° and examined after 2 or 4 weeks.
Pigment analyses were made on six melons
from each storage temperature and examina
tion period. In 1960, two lots of Charleston
Gray melons were stored at 50° and 78°-88°,
and one lot of Congo melons was stored at
50° and 36°. Pigment and reflectance meas
urements were made on six melons per treat
ment after 1 and 2 week storage periods.
It was important that the melons in each lot
be harvested at a similar stage of maturity.
Table
Relation of 3Cnternal Color Ratings to Reflectance and Transmiittance >/alues
1.
ror
Watermelons.
Picmient
Photovolt Reflectance Values
Melon
Visual Color
Rating
No.
Converted C.I.E.
Green
Amber
Blue
filter
filter
filter
Y
X
Percent
Values
y
Transmittance
1
Pink
23.4
33.0
16.1
23.4
.409
.326
52
2
Pink
23.1
32.9
16.8
23.1
.406
.320
45
3
Red
18.4
28.0
11.2
18.4
.436
.328
31
4
Red
17.0
27.5
9.5
17.0
.457
• 327.
27
5
Red
16.6
26.8
10.2
16.6
. 443
.320
27
6
Dark Red
13.8
24.2
7.3
13.8
.480
.320
20
7
Dark Red
12.5
21.6
6.2
12.5
.481
.327
19
8
Dark Red
11.5
20.0
5.9
11.5
.480
.324
16
Table
2.
Effect of Temperature and Duration of Storage on the
Pigment Content
of Watermelons,
Percent Transmittance
At
Storage
Lot
Temp. °F
No.
Season
72-92
1
1959
72-92
2
1959
50
2
72-92
3
50
3
78-38
1
50
1
73-88
2
50
2
50
3
36
3
1959
Harvest
1 week
2 weeks
30.1
22.6
27.0
25.3
27.0
34.5
27.6
23.6
27.6
1960
1960
1960
at
475
mu
Storaqe Duration
4 weeks
26.1
37.9
32.5
23.0
23.4
32.5
35.8
38.4
32.2
22.5
22.7
32.2
33.0
37.3
33.1
38.5
42.6
33.1
33.6
42.2
SHOWALTER: WATERMELON COLOR
and the other half at 36°. Although no decay
symptoms developed at 50° or 36°, the 78°88° treatment was not included because spoilage occurs rapidly at the higher temperatures.
In another experiment to measure the efTable 3.
291
fects of maturation, watermelons of widely
varying maturities were harvested, The reflectance and pigment content were measured
in melons varying in flesh color from pink
to dark red.
Changes In Pigment Content of Six Watermelons after
Storage at 50° and 36QF for 1 and 2 weeks•
Percent Transmittance at
Melon
Storage (j1 50O
No.
Harvest
1 week
F.
Storagei
2 weeks
1 week
at 36°
2 weeks
31.5
37.5
43.5
39.0
42.0
2
31.0
34.2
33.5
37.0
40.0
3
27.0
33.0
37.0
34.0
33.5
4
35.0
41.5
44.5
40.5
43.5
5
44.0
43.0
48.5
45.5
50.0
6
30.0
37.0
43.5
35.5
39.5
33.1
38.5
42.6
38.6
42.2
Mean
Table 4.
Effect of Temperature and Duration of Storage on the Internal Color of
Watermelons as Measured with the Photovolt Reflection Meter
Lot
No.
Reflectance
Variety
Value
At
Harvest
Storage Temperature and Duration
•1 Week
:
2 Weeks
Temp. 78-83°
1
Charleston
Gray
Charleston
Gray
Temp.
2 Weeks
50°
17.5
14.1
Amber Filter
14.4
27.8
18.5
23.2
19.3
Blue Filter
22.9
11.2
23.2
7.8
23.9
7.5
12.8
12.5
CI.E.
• 441
.461
.459
.425
.427
x
Temp.
50°
Green Filter
17.2
13.2
Amber Filter
13.7
27.0
19.3
23.1
Blue Filter
23.0
11.0
29.9
7.3
30.8
8;4
13.0
13.9
CI.E.
.439
.475
.453
.427
.422
x.
Temp.
Congo
1 Week :
Green Filter
Temp. 78-38°
2
3
475 nip
Green Filter
50°
Temp.
20.8
36°
Amber Filter
17.3
26.9
23.3
33.7
24.9
24.4
35.0
24.2
Blue Filter
10.1
34.6
15.2
34.4
16.3
16.0
16.1
C.I.E.
.444
.419
.412
.414
.413
x
FLORIDA STATE HORTICULTURAL SOCIETY, 1960
292
harvest level at the end of the two week
Results
Measurements of the pigment content of
eight melons having a wide range of maturity
(Table 1) yielded transmittance values rang
ing from 52 for an immature melon to 16 for
a fully mature melon. Excellent precision was
obtained between duplicate samples of blend
ed melon used for pigment extraction.
Reflectance measurements
(Table
1)
for
the melons of varying maturities were gener
ally higher for the pink, immature melons and
lower for the dark red, mature melons. How
ever, the range in reflectance values was not
as great, nor the correlation with visual color
as good, as it was for the transmittance values
from the same melons. Since the values ob
tained with the tristimulus filters cannot be
interpreted in terms of visual colors, they were
converted to C.I.E. values according to the
formulas of Hunter (2). The green filter
values are equal to Y values and indicate light
ness or luminance. The amber and blue filter
values were converted to chromaticity coordi
nates x and y.
The Y values decreased as the maturity
ratings progressed from pink to dark red. The
y values showed no changes which correlated
with watermelon colors. The x values were
inversely related to the Y values and the
transmittance values. When the x and y points
in Table 1 were located on a chromaticity
diagram the .480 point was redder than the
.409
point.
During the 1959 and 1960 seasons, the 5
lots (Table 2) of melons stored for two week
periods at high fluctuating summer tempera
tures showed a considerable decrease in trans
mittance compared with the levels at harvest.
The internal color also became redder in 2
lots stored for 1 week and 1 lot stored for 4
weeks at high temperatures. The transmit
tance values in Table 2 are all averages ob
tained from the analyses of 6 melons in each
treatment.
In each of the 5 lots stored at 50° there
was an increase in transmittance, and the
melons were not as red visually as they were
at harvest. In the Congo melons where the
same melons were sampled before and after
storage (Table 3), there was an average in
crease in transmittance of 17 percent during 1
week at both 50° and 36°. The increase in
transmittance continued during the second
week and was 28 and 29 percent above the
period.
Reflectance measurements were made only
on the 3 lots of melons studied in 1960. The
values obtained with the three filters of the
reflection meter (Table 4) show a general
decrease during storage at 78°-88° and an in
crease at 50°. There was a decrease of about
20 percent in green filter values (luminance)
at the higher temperatures and an increase of
about 15 percent at 50°.
When the amber and blue filter values
were converted to x and y values, little differ
ence in y values was noted among the treat
ments. However, the x values for the melons
stored at high temperatures were always
higher than the initial samples, and the x
values for the melons stored at 50° and 36°
were always lower than the initial samples.
The similarity of the x values obtained at
50° and 36° indicated little difference in
response of the melons to the temperature
difference of 14 degrees.
Discussion and Summary
Changes in redness in watermelons during
maturation and storage were measured by
pigment extraction and light reflectance.
Differences in total extracted pigments were
measured as percent transmittance with the
Spectronic 20 colorimeter. Changes in red
ness were associated with the x values of
the C.I.E. color scale computed from the
tristimulus readings of the Photovolt Reflec
tion Meter.
Watermelons increased in pigment content
and redness during storage for two weeks at
72°-92°F. Ezell and Wilcox (1) attributed
the decrease in carotenoid pigments in sweet
potatoes stored at 50° to chilling injury. The
decrease in pigment content and redness of
watermelons during storage at 50° and 36°
may also result from chilling injury since
watermelons develop other symptoms of chill
ing injury at these temperatures. The absence
of a good red color in some watermelons
harvested early in the spring could also be
due to field temperatures too low for normal
color development.
LITERATURE
CITED
1.
Ezell, B. D. and M. S. Wilcox. Influence of Storage
Temperature on Carotene, Total Carotenoids and Ascorbic
Acid Content of Sweet Potatoes. Plant Physiology 27:
81-94.
1952.
2. Hunter, R. S. Photoelectric Tristimulus Colorimetry with
Three Filters. U. S. Department of Commerce Circular C 429.
1942.
KEW AND VELDHUIS: PECTINESTERASE
3.
Kramer, A. and I. C. Haut. Ripeness and Color Studies
with Raw and Canned Peaches. Proc. Amer. Soc. Hort. Sci.
51: 219-224. 1952.
4. Showalter, R. K., S. A. Harmon, B. B. Brantley, D.
W. Newsom, and J. F. Pittman. Changes in Congo Water
melons After Harvest. Proc. Assn. Sou. Agr. Workers. 52.
136-137. 1955.
293
5. Vogele, A. C. Effect of Environmental Factors upon
the Color of the Tomato and the Watermelon. Plant Physi
ology
12: 929-955.
1937.
6. Zechmeister, L. and A. Polgar. The Carotenoid and
Provitamin A Content of the Watermelon. Jour. Biol. Chem
istry
139:
193-206.
1941.
CITRUS PECTINESTERASE INHIBITOR IN GRAPE LEAF
EXTRACT
with distilled water was followed by drying
Theo. J. Kew and M. K. Veldhuis
U. S. Fruit h- Vegetable Products Laboratory1
Winter Haven
Freshly prepared citrus juices are normally
cloudy. Preservation of this cloud is of con
cern to the producers of frozen concentrates
and chilled juices. It has long been recognized
that activity of the enzyne pectinesterase
(PE) is generally associated with cloud insta
bility in orange juice and a correlation has
been observed (4). Complete or partial inactivation or inhibition of the PE is therefore
desirable.
Current methods for inactivating the en
zyme involve the use of heat, which may
affect the fresh flavor of juice products.
Control of enzyme activity by means other
than heat might be advantageous. Bell and
Etchells (1) found an inhibitor of the enzyme
polygalacturonase and cellulase in a water
extract of grape leaves. Etchells, Bell, and
Williams (3) used the extract to control soft
ening of cucumber pickles during fermenta
tion. Their work suggested the search for an
inhibitor of PE from similar sources.
Experimental Methods
Raw Materials. Leaves of domestic musca
dine grapes (Vitis rotundifolia, Michx.) were
obtained from the vineyard of Dr. Charles
Demko, Altoona, Florida. Varieties included
Topsail, Stuckey, Tar Heel, and Thomas x
Munsoniana. Leaves were also obtained from
wild grape (Vitis munsoniana, Simpson) wide
ly distributed in central Florida.
The leaves were transported to the labora
tory promptly after picking and rinsed in tap
water. They were then dipped in dilute hydro
chloric acid solution and rinsed again with tap
water to remove spray residue. A final rinse
lOne of the laboratories of the Southern Utilization Re
search and Development Division, Agricultural Research Serv
ice, U. S. Department of Agriculture.
v
in a current of air. Part of the leaves were
used to prepare an extract and part were
frozen for future use.
Preparation of extract: The stems were re
moved and 40 g. of leaf tissue were com
minuted with 400 g. distilled water for 3
minutes in a high speed blender. The mixture
was strained through four layers of cheese
cloth, then centrifuged in 50 ml. tubes for 10
minutes at 1400 r.p.m. with a tip radius of 8
inches. Sediment was discarded. The super
natant extract was used in this study and here
after referred to as GLE.
Partial purification of the wild grape leaf
extract was effected by concentrating 5 vol
umes to 1 under vacuum, and extracting re
peatedly with ethyl ether. The active principle
was returned to water solution, for comparison
with the crude extract, by evaporation of the
ether in the presence of distilled water.
Pectinesterase activity. PE activity was de
termined by the method published by MacDonnell, Jansen, and Lineweaver (7) and
further described by Bissett, Veldhuis, and
Rushing (2), except that a more concentrated
solution of pectin (2%) was used to facilitate
manipulation of concentrations. In this method
the reaction mixture is adjusted to pH 7.5 and
diluted to 40 ml., after which the rate of reac
tion is measured. Dilution is normally made
with distilled water. For the study of its inhibi
tory effect, GLE was added in place of part of
the water. It was therefore not necessary to
individually dilute each control sample with
out inhibitor to compare activities. Activities
were
expressed
as
pectinesterase units
per
milliliter of single strength or reconstituted
orange juice
mklO4).
multiplied
by
10,000
(PEu/
Cloud retention by visual observation. Por
tions
of
reconstituted
orange
juices
were
placed in 1 x 8 inch test tubes fitted with