YIELD, COLOR AND SENSORY ATTRIBUTES OF PASTEURIZED WATERMELON JUICE’

J. L. SILVA’ AND R. S. CHAMUL

Department of Food Science and Technology, Mississippi State University,

Mississippi State, Mississippi 39762.

Accepted for Publication March 12, 1991

ABSTRACT

Watermelon juice was pasteurized and held for 3 months at 2°C. Juice yields obtained from whole watermelons ranged, between 42 to 50%, depending on culti- Val: Watermelon juice was pasteurized at 76.6”C for 17 s and held at 2°C for 3 months. The pasteurized juice was slightly darker but redder (higher hue) than the raw juice, even though the intensity (chroma) dropped after storage. Taste panelists rated the pasteurized juice (fresh and stored) the same as raw juice in color, appearance and sweetness indicating no loss of color, no phase separation, and no evidence of caramelization. The pasteurized juice samples were rated higher on.fla- vor than the raw samples because of a ‘@-assy” off-jlavor detected in the raw juice.

INTRODUCTION Watermelons (Citrullus lanatus) are grown widely in the southeastern United

States. They are larger and have thicker rinds than those grown in other areas (Dupree et al. 1953). Watermelons are usually grown for the fresh market, but there is an increasing demand for watermelon juice (Anon. 1980).

About 50% of the watermelon fruit is usually pulp, depending on cultivar and size (Dupree et al. 1953). After extraction with a screw-type finisher, about 85% of the pulp is juice (Crandall and Kesterson 1981). The juice is refreshing and has a sweet taste, but the flavor is unstable (Nip et al. 1969). There have been several attempts at preserving the juice, by concentrating, syrup making, or mixing with other juices to make drinks (Huor et al. 1980a, 1980b; Webster and Romshe 1951). These attempts have been unsuccessful in making a good quality, 100% watermelon juice product.

‘Approved for publication as Journal Article No. 5-7263 of the Mississippi Agricultural and Forestry Experiment Station, Mississippi State University. ‘Mail Correspondence to: J. L. Silva, P. 0. Drawer T, Mississippi State, MS 39762. (601) 325-3223

Journal of Foodservice Systems 6 (1991) 141-146. AlLRights Reserved. 0 Copyright 1991 by Food & Nutrition Press, inc., Trumbuil. Connecticut. 141

142 J.L. SILVA and R.S. CHAMUL

Gusina and Trostinskaya (1 974) mixed watermelon juice with apple paste, sugar and citric acid; however, they did not mention the product’s shelf life or how it was preserved. Canned or bottled watermelon juice, with a weak organic acid added, processed at 87.8-l0O0C, was shown to have good color and flavor (Yawger 1942). A concentrated (65”Brix) watermelon juice product was reported to hold its flavor stable for up to 18 months at -21 “C, without color loss (Huor et al. 1980a). However, syrup made from watermelon juice was found to lack water- melon flavor and to have an aftertaste (Webster and Romshe 1951).

In same cases, watermelon juice has been mixed with grapefruit juice to improve the color stability (lycopene) of the product (Huor et al. 1980b). A fruit punch containing up to 80% watermelon juice was developed by Huor et al. ( 1980~).

There is little data available on the stability of pasteurized watermelon juice, even though it is widely accepted that watermelon juice loses its flavor due to enzymatic degradation if it is not heated. This study was conducted to evaluate the quality of pasteurized watermelon juice before and after storage for 3 months at 2 °C and to compare it to the quality of freshly prepared unpasteurized juice.

MATERIALS AND METHODS

This experiment was accomplished in two phases. The first phase was to eval- uate the yield of watermelon juice from two different cultivars: “Jubilee” and “Congo.” The juice was obtained by manually cutting the melons in pieces, sepa- rating the pulp from the rind using a knife, and extracting the juice using a pulper/finisher with a 0.1 14 cm (0.045 in.) screen (Langsenkamp, Indianapolis, IN). A total of 19 melons of each cultivar were evaluated.

The second phase of this experiment was to extract the juice as mentioned in phase I, pasteurize it in a pilot plant HTST pasteurization unit (APV CREPACO, Tonawanda, NY) at 76.7”C for 17 s, cooling to 7°C. This process insured no residual enzymatic activity. The juice averaged 9% Brix and pH of 5.7. The juice was evaluated versus an unpasteurized sample, with part of a pasteurized sample held at 2°C for 3 months for later evaluation. Flavor, sweetness, appearance (homogeneity), and color (redness) were evaluated by 11 trained sensory panelists using a 7-point rating scale. Evaluations were performed on the unpasteurized (raw) juice (0 months), on the fresh pasteurized juice, and pasteurized juice after 3 months storage at 2”C, by the same panelists. Color of the juice was measured using a LABSCAN Model 6000 0”/45” Spectrocolorimeter (Hunter Associates Laboratory, Inc., Roston, VA). Hunter “L” (lightness), “a” (redness), “b” (yel- lowness), saturation index [SI=(a’ + b’) ‘P I , and hue angle [O=tan-’(b/a)], were measured or calculated.

Standard analysis of variance techniques were used and where significant dif-

PASTEURIZED WATERMELON JUICE 143

ferences were found, means were separated by Least Significant Difference (LSD) (Steel and Tome 1980). Data were analyzed by the ANOVA procedure using the Statistical Analysis System (SAS 1985).

RESULTS AND DISCUSSION

Pulp and juice yields were higher from “Jubilee” than from “Congo” cv. (Table 1). This is explained by the fact that “Congo” watermelons have a thicker rind than “Jubilee” (Anon. 1987). However, both cultivars yielded the same amount of juice, 93.2%, from the pulp.

TABLE 1. PULP AND JUICE YIELDS FROM 2 WATERMELON CULTIVARS

C u l t i v a r Pulp YieldX J u i c e YieldY J u i c e from Pulpz ( 0 )

Congo 45.0 41.9 93.2

J u b i l e e 54.1 50.5 93.2

LSD (0.05) 2.14 O v e r a l l Mean 49.6 C.V. ( % ) 6.3 SEM 1.02

3.32 46.2 10.6 1.58

4.94 93.2 7.6

2.35

“Pulp Yield = (Pulp WtiWhole Wt) x 100. ’Juice Yield = (Juice WtiWhole Wt) x 100.

&Juice from Pulp = (Juice Wt/Pulp Wt) x 100.

Hunter color readings for raw and pasteurized juices are shown in Table 2. The fresh pasteurized juice was darker (L=30.70) than the raw juice, (L=35.11) but the pasteurized juice stored for 3 months was the lightest (L=38.95) The juice became redder (decreased hue angle) with pasteurization, and the intensity of the color or saturation (SI) decreased with pasteurization and again during refrigerated storage. The loss of red color and increase in darkening may be the result of loss of lycopene, the pigment responsible for the red color of the fruit (Hulme 1971); and to browning caused by heating of pasteurization, and oxidation during storage. This loss of pigments may be responsible for the higher L reading (clearer product).

I44 J.L. SILVA and R.S. CHAMUL

TABLE 2. HUNTER COLOR READINGS OF RAW AND PASTEURIZED

WATERMELON JUICE

Treatment L a b Hue angleX ChromaY

Raw 35.11 30.91 16.72 28.4 35.15

Pasteurized 30.70 30.28 10.98 19.9 32.22 ( 0 months)

Pasteurized 38.95 17.58 5.04 16.0 18.29 ( 3 months)

LSD (0.05) 2.06 1.66 0.97 2.12 1.48 Overall Mean 31.59 26.27 10.91 21.41 28.55 C.V. ( % ) 4.11 3.17 4.47 4.93 2.59 SEM 1.69 0.69 0.24 0.86 0.55

”Hue angle, 6 = tan- I (bh). ’Saturation Index, SI = (a’ + b’), ’”

TABLE 3. MEAN SCORES FOR SENSORY ATTRIBUTES OF RAW AND PASTEURIZED

WATERMELON JUICES

Treatment ColorX Appearance’ SweetnessX Flavor’

Raw 5.62 6.25 4.00 3.81

pasteurized 6.25 5.87 ( 0 months )

Pasteurized 6.50 ( 3 months)

LSD (0.05) 1.32 Overall Mean 6.12 C . V . ( % ) 24.86 SEM 2.19

5.75

1.37 5.96 24.73 2.37

4.37 5.12

4.75 5.37

1.43 1.15 4.37 4.79 36.13 27.36 2.59 1.67

“On a scale of I to 7 with 7 being “like extremely.”

PASTEURIZED WATERMELON JUICE 145

Sensory evaluations for color, appearance, sweetness, and flavor are shown in Table 3. The sensory panelists did not find any differences in color, appearance or sweetness between the three juice samples. It is evident that even though Hunter readings show an increase in redness and a decrease in color intensity of the juice, the changes were not sufficient to be detected by the panelists. Moreover, the pan- elists rated the pasteurized juices, both fresh and after 3 months of storage, higher in color and flavor than the raw, fresh juice. Panelists detected a "grassy" flavor in the raw juice which is probably the result of peroxidases and other enzyme sys- tems, which are inactivated by pasteurization temperature.

CONCLUSIONS

Pasteurized watermelon juice appears to keep well in storage for 3 months at 2°C. Even though there were slight losses in color and an apparent increase in darkening, the pasteurized juice was rated higher in flavor and color than fresh juice.

ACKNOWLEDGMENTS

The authors express their appreciation to Dr. C. W. Shannon, Dr. R. Q. Scott, Mr. N. Hall, the MSU Dairy Science Department, and to the many students that helped in the processing of the product. They thank Drs. J.O. Hearnsberger, F. B. Matta and C. Boyle (Statistician) for their comments on the manuscript.

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