Quality Acceptance of Juices of Two Cultivars of Muscadine Grapes Mixed with Other Juices

Juices from 2 cultivars of muscadine grapes (Vitis rotundifolia Michx.), 'Noble' (dark-skinned) and 'Carlos' (bronze-skinned), were mixed with juices of 'Concord' and 'Niagara' grapes, cranberry or apple. 'Noble' juice, combined with 'Concord' juice, resulted in the highest quality among the dark mixtures prepared. Also, the mixtures retained most color and flavor during a 12 month storage period. 'Carlos' juice rated higher in quality when blended with the light-colored juices of apple and 'Niagara' than with the dark colored juice. The light amber color was stable during a 12 month storage period, and the flavor and overall acceptance of the mixture were rated higher than for the others. Muscadine grapes are well adapted to the southern United States. The development of new cultivars of both bronze-skinned and black-skinned muscadines has expanded acreage. However, markets for either juice or wine have been too limited to consume the total production of grapes. The influence of cultivar, processing methodology, and storage on juice quality of muscadine grapes has been elucidated (1, 2, 3, 4, 7, 8, 9). Low extraction temperatures have been found to result in improved juice flavor (2, 7, 8). Some of the cultivars are high in acidity, whereas others are high in total phenols (1, 8, 9), resulting in poor acceptance of the single strength juice of certain cultivars. By diluting hot-pressed juice with 40% water and adjusting the sugar level, Sistrunk and Morris (7) improved juice flavor and overall acceptance of 'Carlos' and 'Noble'. Also, by increasing the soluble solids from 17% to 20% by the addition of sugar, the overall acceptance was increased significantly over the control. According to Flora (1), cold-pressed juice from a number of cultivars was rated higher in flavor than hot-pressed juice. In other studies, he demonstrated that blends of muscadine and other fruit juices rated high in quality (5). Pressing muscadine grapes without heating creates at least 4 problems: 1) enzymes that promote browning are not inactivated; 2) juice yield from the grapes is poor because of the thick skins; 3) color extraction of dark-skinned cultivars is low; and 4) a high percentage of the flavor of all cultivars remains in the skins. It has been shown that by crushing the grapes and adding polygalacturonase and SO2, followed by holding the grapes for 24 hr at room temperature, the extraction of color and flavor is sufficient to produce high quality juice (8). There is a widespread interest in high quality grape and other juices to market as nonalcoholic drinks. In order to make recommendations on methods of processing and on suitable juice combinations with muscadine juice, more research is needed. The objectives of the present study were to determine the most acceptable juices to blend with muscadine juice and to assess the stability of the blends during storage. Materials and Methods Two cultivars of muscadine grapes, 'Carlos' (bronze-skinned) and 'Noble' (black-skinned) were obtained from a commercial vineyard in Eastern Arkansas. Two cultivars of American grapes, 'Concord' and 'Niagara,' were grown at the main Arkansas Agricultural Experiment Station Fayetteville. All cultivars were harvested at optimum maturity when soluble solids were above 15%. National brands of cranberry and apple juices to blend with muscadine juice were bought at a local supermarket. Received for publication 27 Aug. 1984. Published with the approval of the Director, Arkansas Agr. Expt. Sta. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. Professor. Table 1. Main effects of mixture and storage on quality of 'Noble' juice. Color difference Soluble Titratable SS/acid Main effects L a b solids (%) pH acidity (%) ratio Mixture (%) Noble 100 12.8 g 12.0 f 1.7 g 16.5 a 3.49 a 0.39 de 43.0 a Apple 75 14.7 f 17.9 d 3.5 d 14.2 cd 3.45 b 0.37 a 38.1 be Cranberry 75 14.9 f 17.4 de 3.2 de 15.5 b 3.28 ef 0.39 de 39.8 b Carlos 75 14.8 f 17.0 a 3.1 a 15.1 bcd 3.34 d 0.40 de 38.1 be Apple 50 18.4 b 23.4 a 5.3 b 13.0 a 3.44 be 0.39 de 33.0 de Cranberry 50 16.6 d 23.0 ab 5.1 be 14.2 d 3.13 h 0.44 c 32.2 e Carlos 50 17.3 c 22.1 b 5.0 c 14.7 bed 3.25 fg 0.44 c 33.2 de Concord 50 15.7 a 18.5 d 3.4 de 15.3 be 3.24 g 0.58 a 26.3 f Niagara 50 17.9 be 22.8 ab 5.2 be 15.1 bcd 3.42 c 0.41 cd 36.5 c Concord 25 14.8 f 16.7 a 2.8 f 14.6 bed 3.28 a 0.50 b 30.6 e Niagara 25 21.6 a 20.5 c 6.0 a 15.2 bed 3.43 be 0.43 c 35.9 ed Storage time (months) 0 14.9 c 17.7 b 2.7 c 14.9 a --0.43 a 35.9 a 6 15.3 b 17.9 b 3.2 b 15.0 a --0.42 a 36.0 a 12 18.7 a 22.0 a 6.1 a 14.6 a --0.44 a 33.5 b The mixtures contained 25%n to 100% `Noble' juice blended with 25% to 75% other juices. Means separated in columns by main effects by Duncan's multiple range test at 5%. Each mean represents 6 individual observations for mixture and 22 for storage. Table 2. Main effects of mixture and storage on sensory quality of 'Noble' juice Overall Acid/sugar Main effects Color Flavor Browning acceptance balance Mixture (%) Noble 100 8.1 ab 6.2 de 7.7 a 6.6 be 6.2 d Apple 75 8.0 ab 6.3 cde 7.7 a 6.5 be 6.3 d Cranberry 75 8.0 ab 6.8 abcd 7.5 a 6.5 be 6.1 d Carlos 75 8.1 a 6.0 a 7.7 a 6.5 be 6.0 d Apple 50 7.3 c 6.3 cde 7.0 b 6.5 be 6.6 cd Cranberry 50 7.9 ab 7.0 abc 7.6 a 6.7 b 6.6 cd Carlos 50 7.7 be 6.6 bcde 7.5 a 6.6 be 7.1 abc Concord 50 8.0 ab 7.5 a 7.9 a 7.4 a 7.2 ab Niagara 50 7.7 be 6.3 ede 7.6 a 6.5 be 6.4 d Concord 25 8.2 a 7.1 ab 7.9 a 7.4 a 7.3 a Niagara 25 6.5 d 6.7 bed 6.3 a 6.3 c 6.6 bed Storage time (months) 0 8.6 ay 7.5 a 8.6 a 7.4 a 7.0 a 6 7.8 b 6.3 b 7.6 b 6.4 b 6.4 b 12 6.9 c 6.0 c 6.4 c 6.3 c 6.3 b The mixtures contained 25% to 100% 'Noble' juice blended with 25% to 75% other juices. Means separated in columns by main effects by Duncan's multiple range test at 5%. Each mean represents 6 individual observations for mixture and 22 for storage. Table 3. Main effects of mixture and storage on quality of 'Carlos' juice. Color difference Soluble solids Titratable SS/acid Main effects L a b (%) pH acidity (%) ratio Mixture (%) Carlos 100 50.5 b -1.7 a 12.9 b 13.7 be 3.10 f 0.53 be 25.8 def Apple 75 53.0 a 2.9 f 9.8 de 10.8 a 3.34 ab 0.45 ef 23.9 f Cranberry 75 39.7 a 17.0 c 9.6 a 13.6 c 2.85 h 0.55 b 24.8 ef Noble 75 23.3 f 25.1 a 7.3 f 13.6 c 3.18 a 0.48 de 27.8 bed Apple 50 52.4 a 2.0 ef 10.7 c 12.1 d 3.25 cd 0.48 de 25.2 def Cranberry 50 42.6 d 11.4 d 10.3 cd 13.4 c 2.97 g 0.50 cd 27.1 cde Noble 50 17.3 h 22.1 b 5.0 h 14.7 a 3.25 cd 0.44 f 33.2 a Concord 50 23.2 f 22.7 b 6.3 g 14.9 a 3.23 de 0.56 b 26.9 cde Niagara 50 48.8 c 1.4 a 13.7 a 14.5 ab 3.29 be 0.50 cd 28.9 be Concord 25 19.2 g 27.7 b 4.6 h 15.0 a 3.20 a 0.61 a 24.6 ef Niagara 25 48.8 c -2.0 ef 13.6 a 14.7 a 3.36 a 0.48 de 30.3 b Storage time (months) 0 37.1 b 13.0 a 7.2 c 13.9 a --0.50 b 28.1 a 6 37.4 6 9.3 b 9.4 b 13.8 a --0.50 b 28.0 a 12 39.8 a 7.9 c 11.7 a 13.5 a --0.53 a 25.4 b The mixtures contained 25% to 100% 'Carlos' juice blended with 25% to 75% other juices. Means separated in columns by main effects by Duncan's multiple range test at 5%. Each mean represents 6 individual observations for mixture and 22 for storage. Table 4. Main effects of mixture and storage on sensory quality of 'Carlos' juice. Overall Acid/sugar Main effects Color Flavor Browning acceptance balance Mixture (%) Carlos 100 6.7 g 6.5 d 7.1 a 6.6 d 6.6 cd Apple 75 8.1 a 7.8 a 8.3 a 7.7 a 7.6 a Cranberry 75 7.9 ab 6.6 d 8.2 a 6.7 cd 6.3 d Noble 75 7.2 ef 6.9 bcd 7.4 cde 6.8 cd 6.9 bed Apple 50 7.4 de 7.3 b 7.8 b 7.2 b 7.1 abc Cranberry 50 7.5 cd 6.6 d 7.8 b 6.7 cd 6.7 bcd Noble 50 7.7 bc 6.6 cd 7.5 bcd 6.6 d 7.1 abc Concord 50 7.0 f 6.8 cd 7.2 de 6.7 cd 6.8 bcd Niagara 50 7.4 cde 6.8 cd 7.7 bc 7.1 be 7.0 abc Concord 25 7.2 def 7.1 bc 7.2 de 6.8 bcd 6.8 bcd Niagara 25 7.5 cd 7.0 bc 7.7 bc 7.1 be 7.3 ab Storage time (months) 0 8.1a 7.6 a 8.9 a 7.6a 7.7a 6 7.6b 6.6 b 7.8 b 6.6b 6.6b 12 6.6c 6.5 b 6.2 c 6.5b 6.5b The mixtures contained 25% to 100% 'Carlos' juice blended with 25% to 75% other juices. Means separated in columns by main effects by Duncan's multiple range test at 5%. Each mean represents 6 individual observations for mixture and 22 for storage. The fruit of the 2 cultivars of muscadine grapes were hand sorted to remove over and under-ripe fruit and trash before washing in a rotary washer. The 'Concord' and 'Niagara' grapes were not sorted. The 4 separate cultivars were crushed in a grape crusher and extracted by heating the grapes to 60°C, depectinizing for 1 hr with commercial pectinase (Ergazyme 100 from Ciba-Giegy Corp.) and pressing in a rack and cloth press. One hundred mg/liter of SO2, were added during depectinization to prevent browning. The juices were heated to 85° after pressing and stored at 2° in covered polypropylene containers for 2 months to cold-stabilize before bottling and pasteurization. The experiment was designed to maximize the use of the 2 muscadine grape cultivars. Each of the muscadine cultivars was combined in ratios of 75:25, 50:50, and 25:75 with the other 5 juices. No adjustment was made in the soluble solids and acidity of the juice blends in this experiment. After the combinations were mixed, 125 ml bottles were filled and heated to 85°C in a steam box prior to sealing. The bottles were capped, cooled in tap water, and stored in the dark at 24° for 0, 6, and 12 months. The juices were analyzed for percentage of soluble solids, percentage of titratable acidity, color by the Gardner Color Difference meter, and sensory quality at the respective storage times. The initial analyses were performed the following day after bottling, whereas subsequent analyses were made at 6 and 12 months. The color was determined by a Gardner Color Difference Meter standardized to a white plate (L = 93.5; a = 1.4; and b = 3.2). A 10 ml sample of juice was delivered in a plastic cup with an optical glass bottom, and readings were taken with the white plate on top of the cup. Titratable acidity was determined by titrating a 5 ml sample of juice with 0.1 N NaOH to an endpoint of pH 8.4 using a pH meter. Titratable acidity is expressed as percentage of tartaric acid. Soluble solids were determined with a Bausch and Lomb Abbe refractometer and pH was taken on the undiluted juice at 20°C. The soluble solids: acid ratio was calculated by dividing the soluble solids by the titratable acidity. Sensory evaluations for color acceptance, acid:sugar balance, freedom from browning, flavor, and overall acceptance were conducted by a semi-trained panel of 12-15 graduate students and faculty on a 9-point hedonic scale (9 = like extremely to 1 = dislike extremely). All parameters were rated on the same scale. The panelists were instructed in methods of rating the juice and shown representative samples of the product being tested. Sugar:acid balance was defined and explained to the panel as the most pleasing sweet and tart response to attain full flavor of the juice. The dark and light colored juices were rated independently for quality and not compared on the basis of color intensity. Lighting for the tests was a solid bank of fluorescent lights over an open countertop. The data were analyzed by the analysis of variance using the Statistical Analysis System (SAS) by the Univ. of Arkansas Computer Center (6). Means of the main effects are separated by the Duncan option of the SAS. Interactive effects were determined by least significant difference (LSD). Results and Discussion 'Noble' (100% juice) was the darkest colored juice included in this study as shown by the low "L" (lightness) value (Table 1). 'Noble' juice was significantly higher in soluble solids, pH, and soluble solids (SS):acid ratio than the other mixtures. Apple juice, when blended 50:50 with 'Noble', was the lowest in soluble solids. The 'Noble-Concord' blends were highest in acidity and lowest in SS:acid ratio. The 100% 'Concord' juice was the highest in acidity, whereas apple juice was lowest in acidity (data not shown). Most of the juice mixtures contained highly acceptable SS:acid ratios between 30 and 40. Flora (5) indicated that juice blends with SS:acid ratios of 25 to 35 were the most acceptable. The sensory panel rated a number of the mixtures high in color, although mixtures of 'Noble' with 'Concord' (75:25) and with 'Carlos' (25:75) rated highest in color and 'Noble' with 'Niagara' (75:25) was rated the lowest in color (Table 2). In flavor and overall acceptance, the mixtures of 'Noble-Concord' were the most acceptable, while 'Noble' with 'Carlos' (25:75) had the poorest flavor. The acid:sugar balance was rated highest for the 2 'Noble-Concord' mixtures and for 'Noble-Carlos' (50:50). The 2 `Noble-Concord' blends also had the lowest SS:acid ratios (Table 1). The main effects of storage during 12 months on mixtures of `Noble' with other juices showed that "L", "a", and "b" values increased indicating a loss of color and increased browning (Table 1). By 12 months storage, the SS:acid ratio had decreased as a result of slight (nonsignificant) decreases in percentage of soluble solids and increases in acidity. In the panel ratings, there was a significant decrease in all quality attributes at 6 and 12 months of storage (Table 2). 'Carlos', a bronze-skinned grape, alone and in combination with apple and 'Niagara', produced light amber colored juices (high "L" low "a", and high "b") (Table 3). Combinations of 'Carlos' and either 'Concord' or 'Niagara' were significantly increased in soluble solids, whereas 'Carlos' alone and in mixtures with apple and cranberry was among the lowest in soluble solids. 'Carlos' juice normally is higher in acidity and lower in pH than 'Noble.' Consequently, the mixtures were lower in SS:acid ratios than those with 'Noble' juice. Table 5. Interaction of mixture and storage on sensory quality and color difference meter "b" of 'Noble' muscadine juice and other juices.