COLOR AND FLAVOR QUALITIES OF WHITE GRAPEFRUIT: WATERMELON JUICE MIXTURES

S. S. HUOR, E. M. AHMED, R. D. CARTER, and R. L. HUGGART

ABSTRACT The objective of this study was to evaluate color and flavor qualities of white grapefruit (G):watermelon juice (W) mixtures and deter- mine their color stability under various processing and storage con- ditions. Addition of small amounts of 60” Brix W concentration to reconstituted G juice significantly improved its flavor and color. No significant color change was observed in the G:W reconstituted juice mixtures stored in a home refrigerator for 15 days or in pasteurized reconstituted mixtures stored in tin or enamel cans at 0” and 27 “C for 6 wk or in frozen concentrate mixture stored at or below 2°C.

INTRODUCTION COLOR is an important factor in grading grapefruit juice. Twenty and 40% of total possible score are assigned for the color of canned grapefruit juice and frozen concentrated juice, respectively (USDA, 1968, 1970). These regulations accord further importance to color by applying a “limiting rule,” i.e., the product may not have a grade higher than that given to color regardless of the product’s total score. Optimum color of pigmented grapefruit is developed as the fruit mature early in the harvest season, but it fades as the season progresses (Lime et al., 1954; Ting and Deszyck, 1958; Oberbacher, 1960; Meredith et al., 1974). The flesh of pigmented grapefruit might be deep pink or red at the time of processing, but the extracted juice is pale in color. Flesh color is manifested by the embedment of lycopene in the fruit rag and pulp while juice color is provided by the pulp ( 10% maximum) suspended in the juice (Huggart and Ting, 1970). Furthermore, attractively colored juices may also turn dull or brown upon storage under adverse condi- tions (Berry and Veldhuis, 1977).

Attempts to enhance to color of pigmented grapefruit juice were limited in success. Addition of highly colored red grapefruit pulp to the extracted juice to achieve an accepta- ble color (Lime and Griffith, 1960) raised the juice’s pulp content to 12.5% which exceeds the limit for U.S. Grade A grapefruit juice (Huggart and Ting, 1970). Moreover, the added pulp increased the amounts of bitter compounds which resulted in lowering the flavor scores of the juice (Dougherty and Fisher, 1977). The color of extracted juice enhanced with lycopene extract, mixtures of FD&C dyes or synthetic carotenoids faded upon storage at 26.7’C (Hug- gart and Ting, 1970). Stability of the juice color occurred when storage temperature was lowered to O’C, and the product was packaged in enamel lined cans (Huggart and Ting, 1970). Toxicological studies are needed to prove the safety of foods fortified with extracted natural pigments or synthetic dyes.

Authors Huor and Ahmed are affiliated with the Food Science & Human Nutrition Depr., Univ. of Florida, Gainesville, FL 32611. Authors Carter and Huggart are with the Florida Dept. of Citrus, IFAS, Agricultural Research & Education Center, Lake Alfred, FL 33850.

0022-1147/80/0005-1419$02.25/O 01980 Institute of Food Technologists

Lycopene is the major colorant in watermelon juice (Huor et al., 1980a). Watermelon juice concentrated by the thermally accelerated short time evaporator (TASTE) has an attractive color which remains stable under storage at -2l’C for at least 18 months (Huor et al., 1980a). The W concentrate could be used as an ingredient in a fruit juice mixture or juice drink (Huor et al., 1980b), or a juice mix- ture containing G and W juices might produce a product that satisfies consumer demands for a naturally sweetened and colored food beverage.

The purpose of this study was to evaluate the color and flavor qualities of G:W juice mixtures and to study their color stability under various conditions of processing and storage.

MATERIALS & METHODS Materials

Charleston Gray watermelon juice was concentrated by the TASTE process as outlined by Carter (1965) and Huor et al. (1980a). Frozen concentrated G juice (53” Brix) was donated by Ben Hill Griffin, Inc., Frostproof, Fla. under the brand name of Golden Nip. Methods

Flavor enhancement of G juice with W concentrate. G juice con- centrate was reconstituted into three categories of juices having 7”, 9” and 11” Brix. Needed amounts of 60” Brix watermelon concen- trate or sugar solution were added to achieve final Brix:acid ratios ranging from 9.3:1 to 15.1:1.

Each category of juice was tested separately and repeated three times. Each treatment had 13 replications. All treatments within each category of juice were compared for flavor and acceptance, in multiple comparison tests by a sensory panel using a 9-point he- donic scale. Juices were chilled to 5 ? 1°C and poured into coded small plastic cups just prior to sensory evaluation. The cups were placed on a round paper plate to ensure random order of sample presentation.

Color enhancement of white grapefruit juice with watermelon concentrate. Small amounts of 60” Brix W concentrate were added to several plastic bottles each containing 100 ml of G juice reconsti- tuted to 10” Brix from frozen concentrate. The mixture was shaken and let stand to room temperature. It was then shaken again and poured into test-tube cells for comparison with visual color standards in use at AREC, Lake Alfred. The visual scores of these standards ranged from 1-11, with a score of 1 being greenish yellow and 11, good pink color.

Objective measurements were also made, using a Hunter Color Difference Meter Model D25-2 with integrating sphere collector Mo- del D25-P (Hunter Associates Lab., Fairfax, Va.), total transmission mode, and a cell path length of 1 cm. Hunter aL and b, values were converted to saturation index S.I. = c = (a’ + b’)G and hue angle @’ = cos-’ $.

Color stability and storage study of grapefruit-watermelon mix- ture. Three types of juices were chosen for this study: (1) reconsti- tuted juice, (2) frozen concentrate, and (3) pasteurized reconsti- tuted juice. All color measurements and calculations of S.I. and @ were made, using the Hunter meter and system, as previously de- scribed.

Reconstituted juice. Frozen concentrated grapefruit juice (FCG) was reconstituted to 10” Brix to which 1.5% by volume of 60” Brix W concentrate was added. The mixture was shaken and divided into three equal parts in capped l-liter glass bottles and stored at 4.4”C. Measurements were made on aliquots from the glass bottles at 3-day intervals for 15 days. Time was considered as the independent vari- able.

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Volume 45 (19801-JOURNAL OF FOOD SCIENCE-1419

Frozen concentrates. The G was diluted to 45” Brix with water, then 4% by volume of 60” Brix W concentrate was added. The mixture was then weighed into 125 ml Erlenmeyer flasks to ensure that an amount equivalent to 25 ml of concentrated mixture was placed in each flask. The flasks were then stoppered and stored at -18”, 2” and 10°C. Measurements were made once a month for 3 months on samples diluted with 75 ml of water. The experimental design was a 3 x 4 factorial with temperature and time as the 2 factors. The levels were -18”) 2”, and 10°C for factor temperature and 0, 1, and 3 months for factor time.

Table I-Sensorv flavor oreference scoresa of G:W Lice mixture

WG initial o Brix

ml 60” Brixb W cone Brix:Acid

Flavor scorec

7” 0 4 6 8

9” 0 2 3 4

11" 0

2

9.3 5.3a 12.0 5.6a 13.3 6.4b 14.5 6.0b 11.5 6.4x 12.8 6.9xy 13.5 7.ly 14.1 7.2~ 13.4 6.3m 14.0 7.ln 14.6 7.0n

3 15.1 7.ll-i

a g-point hedonic scale: 1 = dislike extremely, and 9 = like extreme- IV.

b ml W concentrate per 100 ml ofG juice. c Means within each G juice type followed by the same letter are

not significantly different at the 0.05 level.

Table P-Sensory acceptance ra rings= of G: W and sugar-sweetened G juice mixtures

Flavor scoreb

Brix:Acid W Sugar

9.3 5.0b 5.0b 12.0 6.4a 6.9a 13.3 6.2a 7.0a 14.5 7.3a 7.4a 11.5 5.oy 5.oy 12.8 5.3x 6.4x 13.5 5.6x 6.2x 14.1 5.8X 7.1x 13.4 5.0m 5.0m 14.0 5.4n 5.4n 14.6 6.0n 6.7n 15.1 6.0n 7.ln

a Multiple difference test; g-point hedonic scale: 1 = extremely in- ferior to reference, 9 = extremely better than reference, and 5 equal to reference.

bml of 60” Brix W or Sugar concentrate per 100 ml G juice. Means within each G juice type followed by the same letter are not statistically different at the 0.05 level.

Table 3-Color enhancement of white grapefruit juice with water- melon concentrate.

Watermelona (ml1 L C e” Rankb

0 56.2 19.1 96.9 2.0 0.5 52.3 19.7 87.1 4.5 1 .o 49.9 20.2 81,2 6.0 1.5 47.6 20.7 76.0 7.0 2.0 45.5 21.5 70.7 10.0 9.0 29.6 28.0 40.5 -

a 60” Brix watermelon added to 100 ml IO” Brix white grapefruit juice.

b Visual score standards of AREC Lake Alfred.

142sJOURNAL OF FOOD SCIENCE-Volume 45 (1980)

Pasteurized reconstituted juice. The reconstituted (;:W mixture was pasteurized in a plate-type heat exchanger at 88°C for 7 set and filled at 85°C into 237 ml tin cans and 178 ml enamel lined cans, steam exhausted, sealed, inverted for 2 min, cooled in a spray of tap water and stored at 0” and 27°C. The enameled cans were not steam exhausted. Triplicate color measurements were made once a week for 6 wk. The experimental design was a 2 x 2 x 7 factorial with type of can, storage temperature, and storage time as the variables.

RESULTS & DISCUSSION

Flavor enhancement of G juice with W concentrate Higher mean sensory flavor scores of G:W juice mixtures

were obtained as the amount of added W concentrate in- creased (Table 1). Larger amounts of W concentrate were needed to cause a noticeable flavor improvement of G juice with a B:A ratio of 9.3 than with G juices having B:A ratios of 11.5 and 13.4. This was probably due to the initial total soluble solids content of G juice. Generally, G:W juice mix- tures having B:A ratios of 13.3: 1 or wider received signifi- cantly higher flavor scores (Table 1). High flavor scores of G:W juice mixtures might have been due to either water- melon flavor imparted by W concentrate or to increased sweetness of the juice mixtures. G sweetened with sugar received sensory acceptance scores similar to G:W juice mixtures (Table 2). This indicates that the improved ratings of G:W mixtures observed in Table 1 may have been in- creased sweetness of these mixtures. Sensory evaluations of both experiments (Tables 1 and 2) were conducted under red lighting to assure that color of the G:W mixture was not considered in the panelists’ response.

Color enhancement of G juice with W concentrale Watermelon concentrate could be added to G juice to

impart desirable red coloration. The addition of 1 .O and 1.5 ml of W concentrate to 100 ml of G juice resulted in a colored juice blend having visual ranks between 6 and 7, hue angles between 76 and 81 and chroma around 20 (Ta- ble 3). This color is similar to that of the best commercial pink grapefruit juices (Huggart, 1978). These juices could be ‘described as reddish yellow according to their hue an- gles: Pale pink juices having visual ranks between 2 and 3, hue angles between 90 and 97 and chroma around 19 could be described as yellow or greenish yellow. The use of W concentrate as a natural colorant to G does not necessitate the need for toxicological studies to prove its safety as might be the case of solvent extracted pigments or syn- thetic colorants.

Huggart et al. (1977) proposed a method to closely pre- dict grapefruit juice visual color scores, using objective col- or measurements of hue angle and chroma. Objective meth- ods have not been officially accepted by the Sta.te of Flori- da and the citrus industry. Thus, the method proposed by Huggart et al. (1977) could be an invaluable tool for assess- ing grapefruit juice color. Use of an objective measurement under a standard light would overcome not only the bias of human eyes, but also the object metamerism of grapefruit juice (Huggart et al., 1977). Color stability and storage study of grapefruit-watermelon mixtures

Reconstituted juice. Color of the reconstituted juice mixture was influenced by storage duration at 4’ + l°C (Table 4). Mixtures stored for 15 days were lighter, more saturated, and their hue angles shifted to more yellow. However, these changes, although statistically significant, were small.

Frozen concentrates. Since the objective of this study was to observe changes in color values over a period of time, mean effects of storage durations were compared within each storage temperature (Table 5). Statistical differ- ences in color values were found at each storage tempera-

WATERMELON/GRAPEFRUIT JUICE MIXTURES. . .

ture; however, little changes were evident during 3 months storage at - 18’C and 2’C and 2 months storage at IO’C (Table 5). Lengthening the storage period to 3 months at 1 O°C resulted in reconstituted frozen concentrates exhibit- ing abrupt changes in all color parameters L, c and 0”. The stored product seemed to become redder when 0” de- creased from 72.1’ after 2 months to a value of 53.9’ after 3 months (Little, 1975; Huggart et al., 1977). In addition, the 3-month stored product also showed less saturation (c) and increased darkening as indicated by the lower L value. Visual evaluation of this stored product indicated that its color is brownish red. Moreover, a fermented odor was de- tected indicating active spoilage of the 3-month sample by microbial agents. Murdock and Hatcher (1977) reported yeast growth in inoculated packs of 45’ Brix orange con- centrates stored at 4.4’C for 2 months but not in 65’C Brix orange concentrate. They also reported slight discoloration of 45’ and 65’ Brix orange juice concentrates after 7 and 15 months storage at -l.l”C, respectively, but not at -9.4’C and -17.8’C. The G:W frozen concentrate used in this study had 45’ Brix. No microbial growth or darkening was evident upon its storage at -18°C and 2’C for 3 months and at 10°C for 2 months. Consequently, 45’ Brix could be stored safely at these temperatures and periods, It is expected that it will store well under commercial bulk storage conditions (barrel containers) where temperatures reach -17.8’C or below for 6 months without danger of microbial spoilage or discoloration.

Pasteurized reconstituted juice. No changes in the color of G:W pasteurized reconstituted juice were found upon storage for 6 wk at 0°C and 27’C. However, means of can type X storage temperature interaction as a function of storage time showed small differences. Mixtures stored in enameled cans and stored at 27°C for 3 wk or longer ex- hibited a loss in their hue angles by about lo while those stored in tin cans showed no color change. This may suggest that pasteurized reconstituted G:W juice mixtures can be stored satisfactorily in either tin or enamel lined cans at 0°C or 27’C for 6 wk. For prolonged storage it might be safer to store the product at low temperatures since G juice tends to darken in containers other than tin can. The tin acts as a bleaching agent to keep the product light (Boyd and Peterson, 1945; Tressler and Joslyn, 1961; National Food Processors Association, 1968). Furthermore, pro- longed storage of the product in tin cans might cause seri- ous detinning problems. Kefford et al. (1959) reported that tin content may reach 150-250 ppm in canned orange juice stored at about 30°C for 6 months or longer. This tin content might not be safe or allowed for infant feeding. The CocEex Alimentarius recently proposed a limit of about 150 ppm tin in orange juice for infants (Berry and Veld- huis, 1977).

W concentrate could be used as an ingredient to manu- facture G:W juice mixtures having higher flavor scores than G juice. No noticeable color changes were observed for the G:W mixture packaged and stored under some commercial conditions. Low storage temperatures are recommended for the prolonged storage of frozen concentrate and pasteur- ized reconstituted G:W juice mixtures.

REFERENCES

Berry, R.E. and Veldhuis. M.K. 1977. Processing of oranges. grape- fruit and tangerines. In “ Citrus Science and Technology.” Ed. Nagi. S., Shaw, P.E., and Veldhuis. M.K.. Vol. 2. Avi Publishing Co., Inc., Westport. Corm.

Boyd, J.M. and Peterson, G.T. 1945. Quality of canned orange juice. Ind. Eng. Chem. 37: 370.

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

Dougherty, M.H. and Fisher, J.F. 1977. Quality of commercial, canned, single-strength grapefruit juice produced in Florida dur- ing the 1975-1976 and 1976-1977 citrus seasons. Proc. Fla. State Hort. Sot. 90: 168.

Table 4-Mean lightness (LI value, chroma (cl, and hue angle (0) of reconstituted grapefruit-watermelon mixtures, as influenced by stor- age duration at 4 + I”@

Storage (davs) L C e

0 :

9 12 15

47.7a 21.29 73.5v 48.1 b 21.2gh 74.ow 49.3c 21.4h 74.2~ 48.7d 21.6i 74.8x 48.5e 21.81 753y 49.3f 22.2k 76.8~

a Means within each column followed by the same letter are not significantly different at 0.05 level.

Table 5-Mean lightness IL) value, chroma (cl and hue angle (8) of grapefruit-watermelon frozen concentrates, as influenced by temper- ature (Tel and storaae duration lTila

Ti (month) L C e”

-18 0 44.6a 21.39 71.ly 1 44.6a 21.39 71 .oy 2 45.2b 20.89 72.4~ 3 44.9b 20.99 73.42

2 0 44.6a 21.39 71.ly 1 44.4a 21.49 71.4y 2 44.7a 2.129 71.6~ 3 43.4b 21.19 71.8~

10 0 44.6a 21.39 71 .ly 1 44.la 21.49 71 .oy 2 43.la 21 .Ogh 72.1 y 3 28.5b 19.9h 53.92

e Means within each storage temperature followed by the same let- ter are not significantly different at 0.05 level.

Huggart, R.L. 1978. Private communications. Agricultural Research and Education Center, Lake Alfred, FL.

Huggart, R.L., Petrus. D.R.. and BusIig, B.S. 1977. Color aspects of commercial eraoefruit iuices. 1966-1977. Proc. Fla. State Hort. sot. 90: 173: - -

Huggart, R.L. and Ting, S.V. 1970. Color standardization of pig- mented ranefruit juices. Proc. Fla. State Hart. Sot. 83: 27.

Huor. S.S.,Ahtned, E.M., and Carter, R.D. 1980a. Concentration of watermelon juice. J. Food Sci. 45: In press.

Huor, S.S., Ahmed, E.M., Rao, P.V.. and Cornell. J.A. 1980b. For- mulation and sensory evaluation of a fruit punch containing wa- termelon juice. J. Food Sci. 45: In press.

Kefford, J.F., McKenzie, H.A., and Thompson, P.C.O. 1959. Effects of oxygen on quality and ascorbic acid retention in canned and frozen orange juices. J. Sci. Food Agric. 10: 51.

Lime, B.J. and Griffiths, F.P. 1960. The preservation of pulp and fortification of late season poorly colored red grapefruit juice. J. Rio Grande Valley Hort. Sot. 14: 88.

Lime, B.J., Stephens, T.S. and Griffiths, F.P. 1954. Processing char- acteristics of colored Texas grapefruit. 1. Color and maturity studies of Ruby Red grapefruit. Food Technol. 8: 566.

Little, A.C. 1975. Off on a tangent. J. Food Sci. 49: 410. Meredith, F.I., Redman, G.H., and Griffith% F.P. 1974. Changesin

lycopene-carotene content and fruit quality of Hudson Red grapefruit. J. Rio Grande Valley Hort. Sot. 28: 149.

Murdock, D.I. and Hatcher, W.S. 1977. Effect of temperature on survival of yeast in 45’ and 65’ Brix orange concentrate. Proc. Fla. State Hort. Sot. 90: 186.

National Food Processors Association. 1968. Containers. In “Labo- ratory Manual for Food Canners and Processors,” Vol. 2, 3rd printing (1978). p. 409. Avi Publishing Co., Inc., Westport, Conn.

Oberbacher, M.F., Ting. S.V.. and Deszyck, E.J. 1960. Internal col- or and carotenoid pigment of Burgundy grapefruit. Proc. Am. Sot. Hort. Sci. 75: 262.

Ting, S.V. and Deszyck, E.J. 1958. The internal color and carote- noid pigments of Florida red and pink grapefruit. Proc. Am. Sot. Hart. Sci. 71: 271.

Tressler, D.K. and Joslyn. M.A. 1961. “Fruits and Vegetable Juice Processing Technology.” Avi Publishing Co., Westport. Conn.

USDA. 1968. United States standards for arades of araoefruit iuice. Consumer & Marketing Service, Washington. D.C.

- _

USDA. 1970. United States standards for grades of frozen concen- trated grapefruit juice. Consumer & Marketing Service. Washine- - ton, D.C.

Ms received 12/18/79; revised 3/20/80; accepted 3128180.

Florida Agricultural Experiment Station Journal Series No. 1887.

Presented at the 39th Annual Meeting of the Institute of Food Technoloaists. St. Louis. MO.. June 10-13. 1979.

Volume 45 (1980)-JOURNAL OF FOOD SCIENCE-1421