KUHN: LYCHEE DEHYDRATION STUDIES 273
DEHYDRATION STUDIES OF LYCHEE FRUIT
G. D. Kuhn1 tion. To study the reduction of moisture in fruit
components during dehydration, 13 groups of 10
Florida Agricultural Experiment Station
fruits were weighed and dried in a dehydrator
Gainesville with atmospheric conditions of 61.5 °C dry bulb
and 43 °C wet bulb (38 percent relative humid
Professional counseling suggested in 1957 that
ity). At 2-hour intervals, one group was re
dried lychee fruits, frequently referred to as
moved from the dehydrator, weighed, peeled, and
"lychee nuts," offered interesting opportunities
pitted. Component weights and moisture con
in domestic and foreign markets (4). Available
tents were determined in the manner described
lychee fruits, sun or charcoal-dried, are from
above. The flesh from each group dried 12 hours
the Orient. While they are of acceptable quality,
or more was diluted with 100 ml of water and
improvements in color, flavor, and stability are
blended 3 minutes in a Model 45 VirTis Homog-
thought to be possible with dehydration of Flor
enizer before moisture analysis.
High Temperature Dehydration Study. Six 2-
Limited studies of lychee dehydration were
pound groups of Clermont and one 4-pound
initiated in 1956 and continued in 1957 (1).
group of Sarasota fruits were selected randomly,
Macfie (3) reported acceptable lychee fruits
treated as shown in Table 1, and dehydrated 22
after drying at 150°F for 42-72 hours, the spe
hours with 61.5°C dry bulb and 43°C wet bulb
cific time being dependent upon fruit charac
air conditions. Component weights and moisture
teristics, relative humidity, and the dehydrator
contents of a 10-fruit subsample from each group
efficiency. Higher drying. temperatures were
were determined immediately after drying and
undesirable because of excessive quality deter
after 2Y2 months in vacuum-sealed cans and in
ioration. However, a 1961 study (2) revealed
unsealed polyethylene bags stored at 21 °C.
extreme bitterness in lychee fruits dried at
Stored lychee nuts were examined for the pres
ence of mold, for bitterness, and for flavor
In 1962, studies with lychee fruits were made
of the moisture reduction in the peel, flesh, and
Low Temperature Dehydration Study. Six
seeds during dehydration; the effects of blanch
2-pound groups of fruits handled and analyzed
ing, sulfiting and citric acid predehydration
in the manner described for the high tempera
treatments; and the effects of 43° and 61.5°C
ture dehydration study were dried with 43 °C
air-drying temperatures upon the quality of the
dry bulb and 26°C wet bulb air conditions until
the final fruit weight reached approximately
Experimental 36 percent of the fresh weight. The predehy
Sixty pounds of the Brewster variety were dration treatments are shown in Table 2.
harvested July 2, 1962, in the Clermont area,
Results and Discussion
and stored in Gainesville at 7°C. Ten pounds
of the Brewster variety were harvested July 2, The percents of fresh fruit components and
1962, in the Sarasota area and stored the fol their respective moisture contents are shown in
lowing day in Gainesville at 7°C. Table 3. Measurements were made on random
Three replications of 20 fruits each from ly selected fruits. The variation between the
Clermont were carefully weighed, peeled, and replications was probably due to the large vari
pitted. Seeds and peel components of each repli ability in fruit and seed size, and perhaps fruit
cation were collected separately, placed in tarred maturity. Approximately 2 percent of the fresh
moisture dishes, weighed, and dried to constant fruit weight was lost as juice while the lychees
weight in a vacuum oven at 70° C. Moisture were being peeled. If it had been collected and
analyses were made in the same manner on 10 g measured with the flesh component, 67 percent
subsamples of the flesh after it had been com of the fresh weight would have been fleshy tissue.
minuted 3 minutes in a Waring Blendor. Moisture Losses in Components During De
Moisture Losses in Components During Dehydra- hydration. The reduction of moisture in fruit
components during dehydration is shown in
lAssistant Food Microbiologist, Department oof Food Tech
nology and Nutrition. Figure 1. Peel moisture was reduced from 69
Florida Agricultural Experiment Stations Journal Series
to 29 percent in the initial 2 hours of drying.
274 FLORIDA STATE HORTICULTURAL SOCIETY, 1962
Table 1- Pretreatments of lychee fruits prior to drying 22 hours at 61.5°C dry
bulb and 43°C wet bulb temperatures.
10 Win. Dip1 10 Min. Dip1 Blanched 2 Hrs. Dip1
Group 1% NaHS03 + 1% NaI3SO3 + 2 Min. at 1% Citric Acid
Code Control 0.51 Citric Acid YL Citric Acid 100°C. + 0-11 NaHSU*
1 Room temperature, approximately 30°C
Pretreatm.nte of lychee fruits dried at 43°C dry bulb
2 Fruit grown in Clermont area and 26°C wet bulb temperatures.
3 Fruit grown in Sarasota area 10 Min. Dip1 2 Hour Dip1 Blanched
Group NaHSO3 + 1% Citric Acid 2 Min. At
Code Control Citric Acid +0.11 NaHSO? 100'C.
The rate of moisture loss from the 4th hour until
the drying was terminated at 26 hours was slow
and nearly constant. This condition would be
expected, because water from the seed and flesh
would be constantly passing through the peel. No
change occurred in the flesh moisture during the
FL3 X X
first 2 hours. After 4 hours, the rate of mois
ture loss from the flesh was rapid and constant.
1 Room temperature, approximately 30°C
Moisture loss from the seeds began after 8 hours
2 Fruit grown in Clermont area
of drying and progressed at a moderate and con
stant rate. The rates of .moisture loss from whole 3 Fruit grown in Sarasota area
fruit and flesh were nearly parallel for approxi-
TaJble 3. Percent of the fresh weight of lychee fruits contributed
by each fruit component and the moisture contents of the
Percent of fruit weight Percent moisture content
Replication Peel Flesh Seed Pee 1 Flesh Seed
1 18.1 64.9 15.0 70. 0 79.,5 44. 6
2 17.6 64.4 16.0 67. 5 78.,9 43. 0
3 17.7 66.7 14.0 70. 5 78.,2 45. 5
Mean 17.8 65.3 15.1 69.4 78.9 44.4
KUHN: LYCHEE DEHYDRATION STUDIES 275
9 12 15 18 27 30
Figure 2. Lychee fruit component percents during dehydration.
Hours or Drying
and low relative humidity. There was a cor
Figure 1. Moiature content of lychee fruit components
during dehydration. responding trend of increased percent peel and
seed relative to flesh. The mean moisture con
mately 16 hours of drying; from 16 hours until tent of all treatments decreased from 30.0 to 21.1
drying was terminated, whole fruit and seed percent in the fruit flesh.
moisture loss rates were similar. The storage stability and quality analyses of
The changes in the component percents during fruits dried at high temperature are reported in
dehydration are shown in Figure 2. The rapid Table 5. In groups CH, EH, and GH, which
weight loss of the peel during the first 2 hours were dried to about 36 percent of their fresh
of drying is reflected in the sharply increased weight, no mold growth was* observed. Fruits of
proportion of flesh. Thereafter, the component other groups, regardless of predehydration treat
percents of peel and seed increased similarly, ment, were partly or entirely infected with Peni-
and the flesh component decreased proportion cillium molds. This indicated that the best con
ately. The fresh and final weights of peel were trol of molding was the reduction of flesh mois
17.8 and 18 percent; for flesh, 65.3 and 47.5; ture to at least less than 30 percent.
and for seed, 15.1 and 32.5. The flesh color of vacuum-sealed fruits seemed
High Temperature Dehydration. The com to be lighter than that of those in unsealed poly
ponent percents and moisture contents of the ethylene; however, an objective analysis was not
flesh immediately after drying and after 2% made. Regardless of predehydration treatment
months' storage are given in Table 4. As expec and growing area, the flesh of the fruits dried
ted with random sampling, much variation was at high temperature was bitter.
observed. But, two trends of this non-replicated Low Temperature Dehydration. At the lower
study warrant comment. temperature of 43 °C dry bulb and 26CC wet bulb,
In groups CH, EH, and GH, fruits were dried the drying time required to reduce the dried fruit
to approximately 36 percent of their fresh weight, weights to approximately 36 percent of their
and the flesh moisture contents were between 25 fresh weights varied with the predehydration
and 28 percent. The fruits of the remaining treatments and the source of fruit. Groups AL,
groups were dried to approximately 38-40 per BL, CL, DL, EL, and FL required 88.5, 78.5,
cent of their fresh weight, and their flesh mois 88.5, 78.5, 64.5, and 53.5 hours, respectively.
ture contents were between 30 and 35 percent, Sarasota fruits, groups EL and FL, required
or proportionally higher. considerably less drying time than Clermont
The data indicated that desiccation of dried fruits. Groups treated by blanching, blanching
fruits probably occurred while they were stored sulfiting, and the 2-hour citric acid-sulfite dip,
unsealed in an air-conditioned room at 21 °C BL, DL, and FL, required significantly less
276 FLORIDA STATE HORTICULTURAL SOCIETY, 1962
Table 4. Relative component percents and flesh moisture content of lychee fruits
after drying at 61.5°C dry bulb and 43°C wet bulb temperatures, and after
2i months storage at 21°C.
of Percent of Component Parts Moisture Content
Group Fresh Peel Seed Flesh Flesh
Code Weight II III"" I II III I II III _I II III
AH 38.7 16.1 17.2 18.9 24.8 28.1 30.7 59.0 56.2 50.1 34.9 40.7 25.3
BH 40.1 17.4 20.3 18.0 29.3 28.2 30.7 53.3 53.8 48.7 34.3 35.1 26.5
CH 36.1 17.0 18.2 19.0 28.1 27.9 30.9 54.9 57.8 47.9 25.5 21.5 20.6
DH 38.1 17.6 19.0 21.0 31.8 22.6 31.6 50.6 58.7 43.2 31.9 38.3 23.7
EH 36.5 18.6 18.5 18.3 30.8 27,4 35.1 50.5 52.9 46.0 26.0 23.6 16.4
FH 38.4 17.9 18.0 19.1 28.9 27.4 27.9 54.0 56.2 50.7 29.9 27.3 14.6
GH 34.4 26.4 21.6 26.4 20.2 23.5 22.6 53.3 52.1 47.3 27.6 22.8 20.9
Mean 37.4 18.7 18.9 20.1 27.7 26.4 29.9 53.7 55.3 47.7 30.0 29.9 21.1
I. No storage following dehydration
II. 2-i months' storage, vacuum sealed
III. 9A months' storage, unsealed polyethylene
Table 5. Moisture contents of flesh and quality indices of lychee fruits dried
22 hours at 61.5°C dry bulb and 43°C wet bulb temperatures, and stored
2* months at 70°C.
Vacuum Sealed Unsealed in Polyethylene
Flesh Moldy Moldy
Moisture Fruit Flesh Fruit Flesh
Code Percent Percent Color Texture Flavor Percent Color Texture Flavor
AH 34.9 53 Light Too Very 55 Brown Good Very
brown moist bitter bitter
BH 34.3 56 Light Moist Bitter 100
CH 25.5 0 Light Too Too 0 Med. Moist Strong
brown moist tart brown and tartness
DH 31.9 25 Brown Good Very 100
EH 26.0 0 Light Good Very 0 Light Moist Very
brown bitter brown and bitter
FH 29.9 62 Light Tough Bitter 50 Light Fair Bitter
GH 27.6 0 Light Good Bitter 0 Med. Good Bitter
drying time than groups of other predehydratior. high temperature experiment. The moisture
treatments. ' contents of the flesh, before and after storage,
The percent components of fruits for this and flesh color, texture, and flavor are shown
experiment are not presented in tabular form in Table 6.
because of their similarity to the data of the The moisture level after drying in group FL
KUHN: LYCHEE DEHYDRATION STUDIES 277
Table 6. Moisture contents and quality indices of lychee fruits after drying at 43°C dry
bulb and 26°C wet bulb temperature, and after storage.
Percent Initial Stored Months
of Flesh Va Sealed hsealed polyethylene
Group Fresh Moisture Moisture *K» Mo i sture TTei
Code Weight Percent Percent Color Texture Flavor Percent Color
AL 35.9 23.1 30.9 Light Moist Fair 24.2 Med.
BL 36.6 24.9 27.9 Light Very Good 21.3 Light Very Good
brown brown good
CL 36.6 22.2 26.9 Light Good Very 23.0 Light Good Very
brown good brown good
DL 36.1 23.6 22.8 Light Very Very 19.6 Med. Very Very
brown good good brown good good
EL 35.2 22.5 Light Fair Fair 25.4 Med. Fair Fair
FL 36.5 29.7 29.4 Very Tough Fair 24.6 Light Tough
Mean 36.1 24.3 27.5 23.0
was 29.7, and 43 percent of the dried fruits and seeds during dehydration; the effects of high
stored unsealed were molded after 2% months. and low (61.5° and 43°C) air drying tempera
The dried fruits of all other groups were free of tures on the quality of atmospherically dehydra
mold growth. Their moisture contents were be ted fruit; and the effects of blanching, sulfiting,
tween 22.5 and 24.9 percent. Desiccation of un and citric acid predehydration treatments on
sealed dried fruits was less noticeable com dried lychee fruit quality were studied.
pared to the same variable of the higher tem The moisture contents of fresh peel, flesh,
perature experiment. and seeds were 69, 79, and 44 percent respec
The flavor was influenced by the predehydra- tively. During dehydration, the moisture level
tion treatment. Blanching and the citric acid- of the peel was reduced rapidly, followed by a
sulfite dips for 10 min. and two hours provided typical falling-rate loss. Moisture reduction in
the most acceptable flavor in dried fruits. Bitter the flesh began after 2 hours, and was rapid
ness was not detected in the flesh of fruits dried and constant thereafter. Water loss from the
at low temperatures. This indicated that the seed did not occur until after 8 hours of drying,
presence of bitterness in the fruit flesh may be whereupon it was slow and constant.
dependent upon the drying temperature. The fruits dried at 43°, low temperature,
A panel evaluated vacuum sealed dried fruits were superior in quality to those dried at 61.5°C,
from the high temperature experiment. After 18 high temperature, which were bitter and tough.
judgements, the order of decreasing preference Panel judgments reflected superior quality in
was CH, EH, GH, FH, and AH. Another panel lychee fruits which were blanched, sulfited, and
evaluated vacuum sealed dried fruits of the low dipped in citric acid prior to drying.
temperature experiment. After 15 judgements, After two months' storage at 21 °C, Peni-
the order of decreasing preference was CL, DL, cillium molds had developed on dried lychee
BL, AL, and FL. fruits, whether vacuum-sealed or in unsealed poly
The preferred fruits from both experiments ethylene bags, provided their flesh moisture con
and imported lychee nuts were evaluated by a tent after dehydration was 30 percent or higher.
third panel. After 15 judgments, the order of LITERATURE CITED
decreasing preference was BL, CL, GH, EH, and 1. Dennison, R. A. and C. B. Hall. Notes on Drying
imported lychee nuts. of Lychees. Proc. Fla. Lychee Growers' Assoc. 25-27. 1957.
2. Kuhn, G. D. Dehydration of Lychees. Progress Re
port, Fla. Agric. Exp. Sta. 1961.
Summary 3. Macfie, G. B., Jr. Lychee Processing Equipment.
Proc. Fla. Lychee Growers' Assoc. 33-35. 1957.
4. Palmer, G. New Developments in Lychee Marketing.
The moisture reduction in fruit peel, flesh, Proc. Fla. Lychee Growers' Assoc. 35-39. 1957.