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DEHYDRATION STUDIES OF LYCHEE FR

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					                                            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.
ida lychees.
                                                                                    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
150°F.
                                                                                    ence     of     mold,    for     bitterness,       and    for   flavor
    In 1962, studies with lychee fruits were made
                                                                                    preference.
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
final product.
                                                                                    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
No. 1581.
                                                                                    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.


                                                            Treatments
                              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*

  AH2            X

  BE2
  CH2
  DH2                                                                                        X

  EH2                                                                                        X

  FH2
  GH3                                X



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.


                                                                                                  Treatments

3 Fruit grown in Sarasota area                                                    10   Min. Dip1         2 Hour Dip1     Blanched

                                                                                0.8
                                                              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
                                                               AL2       X
the drying was terminated at 26 hours was slow
                                                               BL2                                             X
and   nearly   constant.    This   condition   would   be
                                                               CL2                       X
expected, because water from the seed and flesh
                                                               DL2                                                             X
would be constantly passing through the peel. No
                                                               EL3       X
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
                                            component s.



                            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.
        Percent                                                                                                 Percent
           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
                                          brown

  CH         25.5             0           Light        Too           Too             0           Med.    Moist       Strong
                                          brown        moist         tart                        brown    and       tartness
                                                                                                         Tender

  DH         31.9            25           Brown        Good          Very          100
                                                                     bitter

  EH         26.0             0           Light        Good          Very            0           Light   Moist          Very
                                          brown                      bitter                      brown    and           bitter
                                                                                                         Tender


  FH         29.9            62           Light        Tough         Bitter         50           Light   Fair           Bitter
                                          brown                                                  brown

  GH         27.6             0           Light        Good          Bitter          0           Med.    Good           Bitter
                                          brown                                                  brown
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
                                                                                                          fc
                                                                                                             70 °C
               of            Flesh                          Va         Sealed                              hsealed polyethylene
                                                                                                              a led
Group         Fresh         Moisture         Moisture        *K»                                   Mo i sture TTei
                                                                                                                Flesh
Code         Weight         Percent          Percent         Color      Texture        Flavor      Percent      Color

     AL           35.9            23.1             30.9      Light          Moist        Fair          24.2         Med.
                                                             brown                                                  brown

     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
                                                             brown                                                  brown

     FL           36.5            29.7             29.4      Very           Tough        Fair          24.6         Light     Tough
                                                             light                                                  brown
                                                             brown



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.

				
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