CONCENTRATION OF WATERMELON JUICE

S. S. HUOR, E. M. AHMED, and R. 0. CARTER

-ABSTRACT

A high temperatureshort time process was used to produce a 65” Brix concentrate from watermelon juice. Color of the reconstituted juice was similar to color of the fresh juice. The concentrate could be stored at -2lPC for 18 months without color loss. The dominant pigment in the concentrate is lycopene and it could be extracted in a relatively pure form. Watermelon concentrate showed a psuedo- platic behavior with apparent viscosities lower than orange and grapefruit juice concentrates within the shear rates of 2-100 set“.

INTRODUCTION

WATERMELON JUICE has several potential attributes. Its refreshing taste and attractive color led Yawger (1942) to bottle it for Crown Can Company. Watermelon juice con- tains relatively high soluble solids (Huor, 1979), making concentration an attractive process. In addition, water- melon juice contains a fair amount of vitamin C, vitamin A precursor and a high content of potassium which is believed to have valuable dieuretic properties (Gusina and Trostin- skaya, 1974). Texas and Colorado have established “water- melon banks” for people suffering from Kidney ailments (Sackett, 1975). In Russia, watermelon juice has been used as a dietetic drink (Gusina et al., 1971).

Brix was determined with an Abbe refractometer with tempera- ture correction to 20°C. The major pigment in the concentrate was extracted with hexane solvent system and also with chloroform system according to the methods of Zscheile and~Pori:er (1947) as modified by Tomes et al. (1963). Absorption spectra of lycopene extracts were scanned with a Beckman Model 25 Recording Spectra photometer (Beckman Instruments, Fullerton, Calif.) in the visible range, 400-700 nm. The color of the reconstituted concentrates was determined by tristimulus calorimetry using the Gardner Auto- matic Color Difference meter (Gardner Instruments, Bethesda, Md.). The color parameter values of aL and b, were converted to satura- tion index (SI) = c = (a2 + bZ)% and hue angle (0) = co!<’ a/c. Color stability of the TASTE concentrate was determined by storing the concentrate at -21°C for 0, 6, 12, and 18 months. At each storage period, the concentrate was reconstituted and color determined in- strumentally.

The apparent viscosities of 65” Brix watermelon concentrate were determined along with three citrus concentrates (62” Brix orange juice, 66” Brix ‘Honey’ tangerine juice, 53” Brix grapefruit juice) at 25°C with the aid of a Brookfield RVT viscometer (Brook- field Engineering Laboratories, Inc., Stoughton, Mass.) equipped with a constant temperature water bath (25°C) and cylindrical spindles no. 1 for watermelon and ‘Honey’ tangerine and no. 2 for grapefruit and orange juice. Results are expressed as apparent viscos- ities at different shear rates.

The objective of this study was to develop a watermelon juice concentrate using a high temperature-short time pro- cess (HTST).

Percent pulp in the reconstituted juices from watermelon and citrus concentrates were determined according to the standard method (U.S. standards for grades, 1968).

MATERIALS&METHODS

Juice extraction

Table l-Absorption spectra maxima (nm) of watermelon concen- trate and lycopene in chloroform and hexane solvents

Ripe “Charleston Gray” watermelons were cut longitudinally into 4 or 6 wedges. The flesh was then removed and fed directly into a FMC citrus juice finisher. Concentration methods

Watermelon colorant Lvcooenea

Solvent

Chloroform Hexane

460,485,518 450.477.508 458.484.518 448.473.564

The HTST method used was the thermally accelerated short-time evaporation (TASTE) process. ‘The TASTE evaporator (Carter; 196.5, 1979) used was of a pilot plant scale with 4 stages, 3 effects and a capacity of removing 227 kg of water per hour as compared to the available commercial evaporator having 7 stages, 4 effects and 18,000 kg/hr capacity. It was fully automated and could concen- trate single strength juice to 65” Brix in 3-5 min, during which time the juice was maintained at 99°C for 6 sec. This time-temperature provides effective pasteurization of the citrus juices (Carter, 1977). It was assumed that watermelon juice behaves similarly to citrus juices, and pasteurization will be achieved during the concentration process. Concentrate quality evaluation

a Reported by Davies (1974).

Table Z-Color quality for fresh juice and juice reconstituted from watermelon concentrate

L +aL +bL Hue angle SI

Fresh juice (9.8” Brix)

Reconstituted juice (9.8” Brix)

18.5 19.0 10.0 27.8 21.5

21.9 20.3 9.3 24..6 22.3

Standard tomato red 24.5 27.6 13.2 25.6 30.6

The obtained concentrate was examined for soluble-solids con- tents (‘Brix), color, flow behavior, and percent pulp. In addition, color stability of the concentrate during frozen storage at -21°C was determined.

Table 3-Effect of storage duration at -21°C on color of reconsti- tuted watermelon juice concentrate (9.s” BrixP

Color parameter

Storage duration (months)

0 6 12 18

Authors Huor and Ahmad are affiliated with the Food Science & Human Nutrition Dept., Univ. of Florida, Gainesville, FL 3261 1. Author Carter is affiliated with the Florida Dept. of Citrus, IFAS, Agricultural Research & Education Center, Lake Alfred, FL 33950.

L 21.9 ?r 1.2 19.9 t 1.5 21.1 f 1.4 20.4 + 1.3 aL 20.3? 1.6 19.1 * 1.2 19.7 f 2.0 21.0 f 1.3 bL 9.3 f 1.6 8.7 f 0.8 8.9 + 0.9 10.6 f 1.4 e 24.6 f 1.9 24.4 f 1.4 24.3 + 2.0 23.0 f 1.6 C 22.3 f 2.2 21.0 f 1.4 21.6 + 2.1 22.8 f 1.8

0022-1147/80/0003-0718$02.25/O Campbell Standard Tomato Red: L = 24.5, aL = 27.6, bL = 13.2, 0 01980 Institute of Food Technologists = 25.6 and SI = 30.6

a Values are expressed as mean 2 standard deviation.

778-JOURNAL OF FOOD SCIENCE- Volume 45 (1980)

RESULTS&DISCUSSION

Dominant pigment Absorption spectra produced by watermelon colorant in

chloroform and hexane showed characteristic peaks of lyco- pene. Absorption maxima agreed closely with those re- ported for lycopene by Davies (1976) (Table 1) indicating that the extracted colorant is lycopene. It is therefore possi- ble to extract lycopene from watermelon juice concentrate in a relatively pure form for possible use as a natural source of coloring matter for food or for other products. However, its use will depend on the results of toxicological studies proving its safety for human consumption. Color quality of reconstituted juice

Watermelon juice concentrate was reconstituted to 9.8” Brix. The 0 and SI of the reconstituted juice approached the corresponding color values exhibited by the fresh juice (Table 2).

Color stability of the TASTE concentrate during -2l’C storage for 18 months was ascertained by following color changes every 6 months. Concentrate samples were recon- stituted upon removal from storage, and color was meas- ured instrumentally. No differences in color values were observed due to storage (Table 3). Accordingly, the color of watermelon concentrate is quite stable during low tempera- ture storage. Flow behavior

Flow behavior of 6S” Brix watermelon concentrate (WC) was studied in conjunction with three citrus concentrates having 53-66” Brix. Apparent viscosity of WC decreased from 20 to 2 poises as shear rate increased from 2 to 100 set-l indicating a pseudoplastic behavior (Fig. 1). This be- havior was also demonstrated by the value of flow behavior index of WC (II = 0.3514). Other concentrates exhibited similar behavior, except ‘Honey’ tangerine concentrate, which showed a relatively constant apparent viscosity throughout the shear rate range 2-100 set-’ . Flow-behav- ior indices were 0.2110 for orange concentrate, 0.3886 for grapefruit concentrate, and 1.0597 for ‘Honey’ tangerine concentrate. Based upon these observations, ‘Honey’ tanger- ine concentratt, having a relatively constant viscosity’ and a flow-behavior index of nearly equal to 1, can be considered as a Newtonian body. However, this juice was heavily cen- trifuged prior to concentration to 66’ Brix indicating that it contained much less pulp than conventional preparations. This low pulp content (4%) could have resulted in the New- tonian behavior exhibited by this concentrate. Orange and grapefruit concentrates were commercial preparations with pulp content of the reconstituted juices of 12% and lo%, respectively. Reconstituted WC contained 12% pulp. Appar- ent viscosities of WC were higher than those of ‘Honey’ tangerine at shear rates ranging from 2- 18 see-’ but the apparent viscosities of WC were lower than those of grape- fruit and orange concentrates at all shear rates examined.

Watermelon juice concentrate produced by the HTST process exhibited color that was stable during frozen stor- age for 18 months. The color of the reconstituted juice was similar to the color of fresh juice. The lower apparent vis- cosity of WC would require less energy to pump and trans- port within a concentrate processing plant than orange or grapefruit concentrate. It also indicates that additional sav- ings might be achieved by using shear rates higher than 20 set-’ to transfer WC through the processing plant.

REFERENCES

Carter, R.D. 1965. New evaporator boosts concentrated orange juice production. Food Manufacture 148: 48.

Carter, R.D. 1977. Reconstituted Florida orange juice. Production/ Packaging/Distribution. Technical Manual. Fla. Dept. of Citrus, Lakeland, Fla.

Viscosity (poise)

so

40

30

20

IO

0

0

3 I

0 - Graprtruit

A -‘Honey’ Tangorlne

0 - Orange Juice

0 - Watrrmelon

Shear Rate (see-1)

Fig. l-flow behavior of the juice concentrates of watermelon (6s” Brixl, orange (62” Brix), ‘Honey’ tangerine (61? Brixj, and white grapefruit (53” Brix).

Carter. R.D. 1979. Processing grapefruit. In “Fruit and Vegetable Processing Technology,” Ed. Nagy, S. and Shaw, P.E., Avi Pub- lishing Co., Westport, Corm. In press.

Davies, B.H. 1976. Carotenoids. In “Chemistry and Biochemistry of Plant Pigments,” Ed. Goodwin, T.W., 2nd ed. Vol. 2, P. 38. Academic Press, New York, N.Y.

Gusina, G.B., Markh, Z.A., Perlowa, N.D., Bogdanova. Z.N., and Kotova. K.S. 1971. Dietetic juices made from cucurbitaceous fruits. Konserv. Ovoschschesush. Prom. 26(10): 10. [Chem. Abstr. (1972). 76(g): 57922.1

Gusina, G.B. and Trostinskaya, L.O. 1974. Watermelon juice and pulp. Knoserv. Ovoshehesuch. Prom. 3: 17. [Food Sci. Technol. Abstr. (1974). 6(12): 2020.1

Huor, S.S. 1979. Food processing and food product development of watermelon fruit., Citrullus lanatus (Thunberg) Matsumara and Nakai. Ph.D. thesis, University of Florida, Gainesville, FIa.

Sackett. C. 1975. Fruit and vegetable facts and points. United Fresh Fruit & Vegetable Association, Washington, 6.C.

Tomes. J.L.. Johnson. K.W.. and Hess. M. 1963. The carotene Din- me& co&ent of c&in rid-fleshed ‘watermelons. Proc. Am. soi. Hort. Sci 82: 460.

U.S. Department of Agriculture. 1968. United States standards for grades of frozen concentrated grapefruit juice. Consumer and Marketing Service, USDA, Washington, D.C.

Yawger, E.S. Jr. 1942. Preparing watermelon juice for packaging in commercial containers such as cans or bottles. U.S. Patent 2.298.328.

Zscheile, F.P. and Porter, J.S. 1947. Analytical methods for caro- tenes of Lycopersicon species and strains. Anal. Chem: 19: 47.

Ms received E/5/79; revised 1016179; accepted 10/10/79.

Presented in part at the 39th Annual Meeting of the Institute of Food Technologists, St. Louis, MO.. June 10-13, 1979.

Florida Agricultural Experiment Stations Journal Series No. 1876.

The authors wish to express their appreciation to the Florida Watermelon Growers’ Association for its donation of watermelons and to the Florida Department of Citrus for the use of their TASTE evaoorator-

Volume 45 (198OkJOURNAL OF FOOD SCIENCE-719