Sugar and acid compositions in the arils of Litchi chinensis Sonn.:: cultivar differences and evidence for the absence of succinic acid

Quantitative and qualitative changes in sugars and organic acids were investigated in two litchi (Litchi chinensis Sonn.) cultivars, 'Feizixiao' and 'Nuomici', during aril development, and their levels measured in another six cultivars ('Guiwei', 'Sanyuehong', 'Jizuili', 'Xuehuaizi', 'Dahongli' and 'Yuhebao') at maturity. Glucose, fructose and sucrose were the predominant sugars. Litchi cultivars could be classified into three types based on their sugar composition: 1) monosaccharide-prevalent types including cvs. 'Feizixiao','Xuehuaizi' and 'Yuhebao'; 2) disaccharide-prevalent types including cvs. 'Guiwei','Jizuili' and 'Nuomici'; and 3) intermediate types including cvs. 'Sanyuehong' and 'Dahongli'. Differences in sugar compositions between cultivars were associated with differences in the activities of certain key enzymes. Succinic acid, which was previously reported to be one of the major organic acids in litchi arils, was found to be absent in all cultivars tested in this study. The major organic acid in the litchi aril was malic acid; others included tartaric, citric and ascorbic acids. Malic acid levels increased during the early stages of aril development, followed by a dramatic decrease as the fruit approached maturity. The ratio of malic acid to tartaric acid varied from 2.6-5.7 between cultivars. The concentration of ascorbic acid decreased with fruit development until 2 weeks before harvest, when it started to increase slightly as the fruit approached full maturity. Ascorbic acid levels varied considerably among the eight cultivars tested. Monosaccharide-prevalent cultivars contained more ascorbic acid than disaccharide-prevalent cultivars.