Effects of maturity on amino acid nutrition in‘Red Globe’grape (Vitis vinifera L.)

Abstract: 【Objective】The study investigated the amino acid nutrition in‘Red Globe’grape (Vitis vinifera L.) at different maturities and analyzed the contents of 18 amino acids in grape fruit.【Methods】Grape samples were harvested at 88 d, 95 d, 102 d, 109 d, 116 d, and 123 d after full bloom (marked as initial maturity, maturity, complete maturity Ⅰ, complete maturity Ⅱ, over maturity, and senescence), respectively. Ten clusters of grape berries were randomly collected for each period. Ten grape berries were chosen from each cluster for amino acid determination. To detect the content of Trp, sample (2-3 g)was hydrolyzed with 4 mol·L-1 LiOH and analyzed with an auto amino acid analyzer (LC8800, Shimad-zu). For the other 17 amino acids, sample was hydrolyzed in 6 mol·L-1 HCl and detected according to the national standard (GB 5009.124-2016). Amino acids were classified into different groups, such as essential amino acids, non-essential amino acids, essential amino acids for child, medical amino acids, branched chain amino acids, flavoring and coloring amino acids, primary amine amino acids, and spe-cial function amino acids. Based on the obtained data, the amino acid nutrition value was evaluated ac-cording to egg protein model and the ideal model recommended by FAO/WHO. A series of indexes, such as the amino acid score (AAS), chemical score (CS), and score of ratio coefficient of amino acid (SRC), were calculated.【Results】As Gln and Asn were degraded into Glu and Asp under acid hydroly- sis, at least 16 amino acids, including 8 essential amino acids, 2 essential amino acids for child, were found in‘Red Globe’grape during the whole harvesting period. All were components for protein. The contents of essential amino acids, non-essential amino acids, essential amino acids for child, medical amino acids, branched chain amino acids, flavoring and coloring amino acids, primary amine amino ac-ids, and amino acids with special function were in the ranges of 55.73-65.97, 117.63-169.08, 32.68-70.38, 113.00-164.41, 23.17-28.53, 92.61-140.48, 112.60-160.90 and 103.29-151.07 mg·100 g-1, respec-tively. The differences among grape berries at different maturities were significant (p ＜0.05). The high-est values for all indexes were found in the completely mature Ⅰ group. From the maturity to complete-ly maturity Ⅱ, the contents of total amino acids and essential amino acids were higher than that in ap-ple, grapefruit, and tangerine. The content of essential amino acids for child in grape was lower than that in banana, pomegranate, Rosa roxburghii, and Hippophae rhamnoides, but higher than that in ap-ple, peach, orange, kumquat, grapefruit, and tangerine. The percentages of essential amino acids for child, medical amino acids, branched chain amino acids, flavoring and coloring amino acids, primary amine amino acids, and special function amino acids against total amino acids were 18.44%-29.94%,63.34%- 69.95% , 41.58%- 44.57% , 63.34%- 69.95% , 41.58%- 44.57% , 52.25%- 59.77% , 63.53%-68.57%, and 58.28%-64.46%, respectively. The highest values were also found in the completely ma-ture Ⅰ group. The values of E/T and E/N ranged from 31.26% to 36.57% and from 45.48% to 57.65%, respectively. These indexes of grape in all groups except the senescing berries were lower than the stan-dard value recommenced by FAO/WHO. The ratio of content and taste threshold (RCT) was used for evaluating the effects of flavor amino acids on the grape flavor. The RCT of Arg, Asp, and Glu in grape ranged from 2.62 to 6.31, 4.50 to 5.47, and 4.64 to 6.09, respectively, which was higher than that of strawberry and orange. The results indicated that these amino acids were the key amino acids for the fla-vor of grape. Their RCT showed an increase trend firstly, and then declined. The highest RCTs were found in completely maturity Ⅰ. The RCT of the other 12 amino acids were lower than 1. The percent- age of flavoring and coloring amino acids to total amino acids in grape was higher than that of strawber-ry, orange and tangerine. The percentage of primary amine amino acids in grape was higher than that in Chinese kiwifruit and Phyllanthus emblica. The percentage of medical amino acids against total amino acids in grape was higher than that in ginseng, cordyceps sinensis, and Chinese wolfberry. The contents of (Phe+ Tyr), Val, Ile, Leu, Trp, and (Met +Cys) were insufficient, while the contents of Lys and Thr were relatively surplus. The most restricting amino acid in‘Red Globe’grape was Met+Cys. The val-ues of AAS, CS, and SRC of grape with different maturities ranged from 11.33 to 14.07, 18.32 to 24.43, and 49.70 to 57.04, respectively.【Conclusion】The character of amino acid composition in‘Red Globe’grape varied constantly during berry maturation and senescence. The edible value of grape could be improved by complementing with other foods, such as mushroom (rich in Met and Cys) or grain (poor in Lys and Thr).