リンゴの黄色品種の有袋果と無袋果における糖質と有機酸の相違, 並びにそのアントシアニン色素の生成に及ぼす影響

Abstract

Many apple growers in Japan use double paper bags for the yellow colored apple cv. Mutsu, to enhance red color formation and to remove ground color.To study the cause of the red color formation, young fruits of the yellow colored apple cvs, Mutsu and Golden Delicious, were covered individually with commercial double paper bags for shading from early June to late September, according to the usual way in Aomori Prefecture. The fruits were harvested in middle October, and anthocyanin content was measured for bagged and unbagged fruits. The anthocyanin level was greater in bagged fruits than in unbagged ones in both cultivars.Sugars and organic acids in the apple skin of both cultivars obtained from late August to middle October were analyzed by gas chromatography (GC) with a capillary column, after being derivatized with trimethylsilyl agents.In both cultivars, the main sugars were glucose, fructose, sorbitol and sucrose, and the main organic acids were malic and quinic acids. Throughout the period tested, the content of fructose was much higher in the bagged fruit than in the unbagged fruit in both cultivars. But no differences were found in the other main components between bagged and unbagged fruits in either cultivar.Compositional changes in other minor organic acids were also investigated between bagged and unbagged fruits in both cultivars, using GC and gas chromatography-mass spectrometry; citric acid was identified as a component which had the most quantitative difference. A small amount of citric acid was detected before coloring, and it decreased slightly at the later stages of coloring in the unbagged fruit. However, in the bagged fruit, a large amount of citric acid was detected before the stages of coloring, and it decreased remarkably at the later stages.Commercial citric acid (sodium salt) and fructose were applied to disks of unripe skin from bagged and unbagged fruits of both yellow cultivars, and the disks were irradiated with the light of a discharge lamp. When citric acid was applied, the content of anthocyanin increased compared to that of the control only in the skin of the bagged fruit of both cultivars. When fructose was applied, the anthocyanin level in the skin of both cultivars did not increase, regardless of bagging treatment.Thus, citric acid appears to be related to the development of anthocyanin only in bagged fruit of the yellow apple cultivars described above.