Proc. Fla. State Hort. Soc. 91:112-114. 1978.
SECTIONING GRAPEFRUIT BY ENZYME DIGESTION
Joseph H. Bruemmer, Alicia W. Griffin Preliminary tests
U. S. Citrus and Subtropical Products Laboratory1
P. O. Box 1909, Winter Haven, Florida 33880 In our first attempt to peel grapefruit by vacuum in
fusion with solutions of commercial pectinase, we hand-
Oladipo Onayemi scored the peel of a grapefruit in quadrants and placed it in
University oflFE, a solution of 1.0% Irgazyme (one of the commercial
Department of Food Science & Technology pectinases used later in the study) in a vacuum infusion
ILE-IFE, Nigeria apparatus, a heavy-walled glass desiccator connected to a
vacuum pump. We held a vacuum of 28 in. Hg in the ap
paratus for about 5 min, then released the vacuum and re
Additional index words, pectinase.
placed the gas in the fruit with about 100 ml of pectinase
solution. The grapefruit and solution were maintained at
Abstract. Mature 'Duncan' grapefruit were vacuum in room temperature. Within several minutes after infusion,
fused with a solution of commercial pectinase complex to the peel began to slowly disintegrate. The peel was easily
evaluate enzyme digestion as a method for sectionizing. removed, and the slimy coating covering the fruit washed
Treatment with 100 ppm enzyme effectively loosened the away under the faucet with a gentle stream of water. The
peel and segment membranes and freed the intact juice peeled, washed grapefruit was then easily separated into
sections, which could then be easily removed. A 16-member hemispheres, which were then fanned out on a flat surface.
panel of tasters scored the sections "like moderately" for The segment membranes were easily separated from the
flavor and texture. Six commercial pectinase complexes were vesicular tissue, so that intact sections could be removed.
evaluated for effectiveness in preparation of intact sections None of the juice sections were broken.
at standardized treatment conditions (122°F for 30 min). The In preliminary tests, we standardized the pectinase treat
pectinases contained cellulase, pectinesterase, polygalac- ment and determined the minimum effective concentration
turonase and polymethylgalacturonase. Their effectiveness in for each brand of commercial pectinase used. Ease of peel
peeling correlated best with the activities of polygalac- ing, lack of adhering albedo, ease of removing sections from
turonase and polymethylgalacturonase. The major advantage segment walls, and appearance of sections were evaluated
of enzymic digestion is high recovery of high quality sections. and given scores of 1 = good, 2 = fair, or 3 = poor. Con
Because the sections are not cut from the membrane, loss of centrations for each brand were selected so that 45 min of
juice is minimal and dry packaging could be used for market treatment at 50°C (122°F) was adequate for effective treat
ing the product. ment (Table 1).
Table 1. Minimum concentration of 6 brands of pectinases required for
The small portion (2 million boxes) of grapefruit pro effective peeling and sectionizing.2
duction that is processed as sections has remained relatively
constant over the past 5 years. Current processing technology Pectinase brands
is a major deterrent to expanded markets for sections. Proc A B C D E F
essing costs are high because sections must be cut from the
membranes and the yield is only about 60% of the total Pectinase 100 100 500 1000 1000 3000
juice segments. Quality is low because steam peeling, lye (1)
(1) (5) (10) (10) (30)
finishing, and heat pasteurization change the fresh grapefruit Treatment
flavor and texture. Finally, treating and disposing the scores
15 min 10 8 9 11 13 7
alkaline waste water from the lye finisher create problems 30 min 6 6 7 7 8 7
for the processor. We describe and evaluate the use of en 45 min 5 4 4 4 4 4
zyme digestion for peeling and sectionizing grapefruit.
^Criteria of effective peeling and sectionizing: ease of peeling, lack of
adhering albedo; ease in removing sections from segment walls and
Materials and Methods appearance of sections. Scores were determined for each treatment by
assigning the values 1 = good, 2, = fair and 3 = poor for each criterion.
Grapefruit (Citrus paradisi Macfad. cv. Duncan) were Values are the average sums of the four scores for six fruit.
obtained from a local packer. Pectinases were provided by
Grinsted Products, Inc., Overland Park, Kansas; G. B.
Fermentation Industries, Inc., Des Plains, Illinois; Novo Peeling and sectionizing procedure
Laboratories Inc., Wilton, Connecticut; Miles Laboratories,
Inc., Elkhart, Indiana; Enzyme Development Corporation, The effectiveness of pectinase depends on temperature as
New York, New York, and Ciba-Geigy Corporation, Ardsley, well as time. The manufacturers of the various pectinases
New York. Pectin, N.F. #3442 and polygalacturonic acid recommended 122°F2 as the optimum temperature for
#3491 (PGA) were products of Sunkist Groves, Inc., pectinase infusion. To do this without cooking the fruit, we
Corona, California. Carboxymethylcellulose (CMC) was submerged the grapefruit, which had initial temperatures of
obtained from Dow Chemical Co., Midland, Michigan. 68°-77°F, for 30 min in a water bath at 140°F. At the end of
Gelatin was obtained from a local food supplier. the soak, the temperature of the albedo was 122°F, that of
the core, 95°F. The fruit were then removed from the bath,
and their peels were hand-scored from stem-end to blossom-
end, dividing the sphere into six equal parts. The fruit were
^Science and Education Administration, U. S. Department of Agri then submerged in the enzyme solution (which was main
culture, Agricultural Research. Mention of a brand name or trademark
is for identification only and does not constitute endorsement of the
tained at 86°F) contained in the vacuum infusion apparatus.
product by the U. S. Department of Agriculture over others which may
also Y> tofijte 2For metric conversions see table at front of this Yolume. Ed.
112 Proc. Fla. State Hort. Soc, 91: 1978.
We pulled a vacuum of 28 in. Hg and held it for 5 min be The activity of pectinesterase was measured by increase
fore readmitting air into the vessel. We repeated the vacuum in H+ liberated by the enzyme's substrate, pectin, during
infusion and then removed the fruit from the solution and hydrolysis. Fifty ml of 1% pectin solution was heated to
placed them into individual plastic food bags. After incubat 122°F, and 15 ml of dilute pectinase solution was added.
ing the fruit for 30 min in an oven at 122°F, we removed the The temperature was controlled at 122°F in a water-jacketed
fruit from the bags, peeled them, and split the fruit in half, vessel by a thermostatically controlled circulating bath. At
then removed the juice sections from the segment walls. zero time the pH of the solution was adjusted to 4.0 with
0.5 N NaOH. As the reaction proceeded, the pH was mon
Quality of enyzme prepared sections itored and kept at 4.0 by measured addition of 0.1 N NaOH
from a burette. The volume of alkali added to maintain pH
Grapefruit sections prepared by the enzyme digestion 4.0 was recorded every 2 min for 10 min. The volumes of
method were evaluated for quality by comparing them to 0.1 N NaOH consumed were plotted against time and the
sections cut from grapefruit peeled by the conventional slope of the proportionality line was calculated by the
method. Grapefruit for the comparison were obtained from method of least squares. The pectinesterase activity of each
a local canning plant. Steam-peeled, lye-finished grapefruit, brand of pectinase was expressed as the amount that hy-
taken directly from the sectionizing table at the plant were drolyzed pectin at the rate of 20 /Ainoles of ester bonds per
transported to the laboratory in ice chests where sections min at 122°F.
were cut from the fruit segments. Unpeeled grapefruit, also
from the plant, were peeled and sectionized by the pectinase
Results and Discussion
procedure described above. A panel of 20 tasters were pre
sented grapefruit sections prepared by the two methods and Grapefruit sections prepared by pectinase treatment ap
asked to evaluate them and indicate a preference on the peared dry and intact and tasted fresh and clean. The fruit
basis of flavor and texture. The sections were also compared segments were completely recovered as intact sections. In
for juice retention. A weighed portion of the two kinds of contrast, sections prepared by the conventional method of
sections were stored in plastic bags for three days and then cutting appeared wet and smaller because 30 to 40% of the
the sections were drained of juice and reweighed. juice vesicles remained attached to the segment membranes.
The cut sections also sustained a drip loss of over 10% after
Storage stability only 3 days at 40°F, whereas, the new type sections retain all
their juices. In flavor and texture the sections prepared with
Sections were coated with gelatin by dipping chilled pectinase were superior to cut sections. When asked to
sections into 10% gelatin solution maintained at 77°F and evaluate and indicate a preference, all 20 members of a
then setting them on waxed paper at 40°F. Coated and un- laboratory taste panel preferred the new type sections.
coated sections were each packed in polyethylene bags for
Storage of pectinase-peeled sections
A panel of 12 tasters was selected from a group of 19
panelists who were surveyed for preference for grapefruit A panel of tasters judged unpasteurized pectinase-
sections. The panel members were presented with pectinase- prepared sections stored dry or in grapefruit juice to be
prepared grapefruit sections stored dry or in freshly pas similar in flavor and texture during 14 days of storage
teurized grapefruit juice in plastic bags at 40°F. They were (Table 2). These data suggest that flavor and texture of the
asked to score the fruit for flavor and texture on a scale of sections are stable during short-time cold storage.
1 to 9; 1 = like extremely, 9 = dislike extremely (1). For
another storage stability test, each member of a second Table 2. Comparison between sections packed dry and in juice.
panel of 16 to 24 tasters was presented with 2 gelatin-coated
sections stored at 40°F, one in air and the other in N2 and Average hedonic score z
asked to compare the sections for flavor and texture. The Storage Flavor Texture
results of this paired comparison test were examined sta days Dry pack Juice pack Dry pack Juice pack
tistically for significance (1).
1 3.5 3.5 3.1 3.2
Enzyme activity 4 3.3 3.5 3.1 3.3
8 4.0 4.1 2.9 3.0
We also wished to evaluate the effectiveness of com 11 3.7 3.8 2.9 2.9
mercial pectinase preparations; to do this we measured the 14 3.3 4.8 2.5 3.2
activity of the constitutent enzymes. We used two methods
reported by Vas et al. (2). *Twelve panelists scored on «i scale of 1 to 9; 1= like extremely, 9 =
The activities of polygalacturonase, polymethylgalactu- dislike extremely. Values are the mean of 2 samples per panelist.
ronase, and cellulase were measured by decreases in the
specific viscosities of the enzymes' substrates, 1.5% poly-
galacturonic acid, 0.45% pectin, and 2% carboxymethyl- Unpasteurized grapefruit sections coated with gelatin
cellulose, respectively. Solutions of substrate were incubated and stored in N2 were preferred by panelists to coated sec
with one of the pectinases at 122°F in Ostwald-type vis- tions stored in air (Table 3). During the 28-day storage test
cometers (Fisher Scientific Instruments, #150) in a thermo preference was for N2-stored fruit, but only on one trial
statically controlled water bath. The decrease in specific (Exp. 2, 21 days) was this preference statistically significant.
viscosity of each substrate was expressed as the percentage Pectinase-prepared sections can be heat-pasteurized and
of the original and plotted against the log of the incuba canned in juice-syrup, but dry packs of unpasteurized sec
tion time. From each plot the time necessary for 25% re tions have several advantages over conventional packs.
duction of specific viscosity was interpolated. Because the Besides saving the weight and space of the liquid in the pack,
log reciprocal of this time is proportional to the log of the the sections could be displayed in attractive see-through con
enzyme concentration, we were able to calculate the amount tainers. Gel-coating of sections would add structural stability
of each brand of pectinase needed to reduce viscosity by and could serve as a matrix for flavor-stabilizing substrates
25% in 17.5 min. for the metabolically active unpasteurized fruit. For low
Proc. Fla. State Hort. Soc. 91: 1978. 113
Table 3. Paired comparison scores between sections stored in air and in Table 4. Concentration of 6 brands of pectinase required for equivalent
nitrogen.* activity of constituent enzymes.2
Storage Exp. 1 Exp. 2 Enzyme and Pectinase concentration (mg/g substrate)
days substrate ~~A B C D E~ F~
7 13 11 12 5 Polymethylgalacturonase 37 37 111 296 22 1110
14 11 9 11 6 Pectin (1.0) (1.0) (3.0) (8.0) (6.0) (30.0)
21 12 4 15y 5* Polygalacturonase 22 44 56 356 256 589
28 12 8 11 7 PGA (1.0) (2.0) (2.5) (16.0) (11.6) (26.7)
Cellulase 75 83 58 66 16 833
CMC (1.0) (1.1) (0.8) (0.9) (0.2) (11.1)
zScores are the number of tasters who preferred one section over the Pectinesterase 200 200 1300 500 3300 5800
other. Pectin (1.0) (1.0) (6.5) (2.5) (16.5) (29.0)
ySignificantly different at P <0.05.
calorie diet packs, lack of syrups and juice would reduce "Pectin, PGA, and CMC were degraded at the same rate, 25% reduction
sugar and calorie contents, as well. in viscosity in 17.5 min at 50°C. Pectin was demethylated by each brand
at the rate of 20 /tmoles of ester bonds per min at 50° C. Ratios of cone
of all brands to brand A shown in parentheses.
Degradative activity of the pectinases
According to the manufacturers the pectinases contain Conclusion
polymethylgalacturonase, pectinesterase, polygalacturonase,
and cellulase, enzymes that degrade pectin, PGA and CMC. Infusion of commercial pectinases into grapefruit effec
One of these enzymes is more important than the others in tively loosened the peel and segment membranes and freed
peel degradation. Comparison of the enzyme activities with intact juice sections which could then be easily removed.
effectiveness of peeling of the various brands should indicate These sections were superior in size, flavor and texture to
which enzyme is the most important. Pectinase concentra sections cut from steam-peeled, lye-finished fruit. Com
tions necessary for equivalent activity were compared in mercial pectinases differ in their peeling effectiveness and in
Table 4. Brands A and B, which were the most effective in activities of polymethylgalacturonase, polygalacturonase,
peeling, also had the highest activity in degrading pectin pectinesterase and cellulase. Pectinase pelling has potential
and PGA. The concentration ratios for polymethylgalac as a commercial method of preparing grapefruit sections
turonase activity compared favorably with the concentration because segments are completely recovered as high quality
ratios for effective peeling and sectionizing. The concentrate intact sections by this method.
ratios for cellulase activity showed no relationship to effec
tive peeling ratio but the ratios for pectinesterase and poly
galacturonase activities showed some similarity. The data in Literature Cited
Table 4 indicate that pectin degradation could be used as 1. Larmond, E. 1967. Methods for sensory evaluation of food. Publ.
an objective measurement of the peeling effectiveness of a #1284, Canada Dept. of Agric, Ottawa, Canada.
2. Vas, K., M. Nedbalek, H. Scheffer and G. Kovacs-Proszt. 1967.
pectinase. In addition, cellulase activity was not involved in
Methodological investigations on the determination of some pectic
peeling effectiveness. enzymes. Fruchtsaft-Ind. 12(5): 164-184.
Proc. Fla. State Hort. Soc. 91:114-117. 1978.
MICROBIAL ASSESSMENT OF PASTEURIZED-REFRIGERATED
PEACH HALVES IN TRANSPARENT POUCHES1
R. P. Bates, L. Alcantara, J. Gomez and J. A. Koburger perature (20°C) and pouch oxygen permeability selectively
Food Science and Human Nutrition Department, IFAS favored mold development. However, at 2°C, or in the case
University of Florida, Gainesville, FL 32611 of peeled halves, no microbial outgrowth occurred. The
pasteurized-refrigerated process was effective from the stand
Abstract. The microflora of fresh 'Flordagold' peaches point of enzymatic and microbial stability, although the boil-
and microbial changes induced by lye peeling, hot packing in in-bag pouch was a marginal package for ambient tempera
boil-in-bag pouches, pouch steaming (7 min @ 86°C), rapid ture storage.
cooling and storage at 2 and 20°C were evaluated. Prepara
tory steps resulted in a progressive decrease in plate counts Florida is currently developing a modest peach industry
to <50 organisms/g immediately after processing. Die-off based on varieties developed over the last decade. During
proceeded to <l/g during storage except in pouches con this period, acreage in the state has expanded from about
taining unpeeled halves stored at 20C where mold growth, 2,800 to 6,500 (2, 12) and Florida ranks about 10th in U.S.
undetected for the first 2 weeks, proceeded rapidly there peach production (5). Home-grown peach plantings have
after. Apparently, the combination of high levels of initial also increased by a substantial (but undetermined) amount
contamination, low pH (3.5), non-refrigerated storage tem- over the same period. As well as high yield and improved
cultivation characteristics for North Florida, these new
iFlorida Agricultural Experiment Stations Journal Series No. 1479.
varieties ripen early and are well suited for home-grown,
We are grateful to Cryovac Division, W. R. Grace & Co. for a reliable
supply of poudi maieiial and to D. W. Buchanan and E. P. Miller, pick-your-own and local markets.
Fruit Crops Dept., IFAS, for generous access to experimental peach There is now a need to consider expanded markets and
plantings. utilization forms for Florida-grown peaches. Several peach
114 Proc. Fla. State Hori. Soc. 91: 1978.