Changes of sugar and acid composition and content during fruit development in four sweet cherry varieties

【Objective】Sugar and acid components and content are important indicators affecting the flavor and quality of sweet cherry fruit. Many studies of sweet cherry have focused on changes of qualities, sugar and acid contents during fruit development. However, there has been very few study on changes of sugar and acid contents during development of sweet cherry fruits with different flavors and different ripening periods. The objective of the study was to elucidates the dynamic change of sugar and acid during fruit development of sweet cherry with different flavors and different ripening periods, and provide a reference for fruit quality regulation, fertilizer and water management, and timely harvest of sweet cherry fruits.【Methods】The tested varieties included high acidity sweet Cherry cultivarsКрупноплодная, Caihong and low acidity sweet cherry cultivars Zaomilu, Linglongcui. Крупноплодная and Zaomilu are early-repening cultivars, while Caihong and Linglongcui are mediumrepening cultivars. The samples were collected for the first time on the 10th day after flowering, and then collected every 5 days until fruit repening. High- performance liquid chromatographic methods were used to identify and quantify sugar and acid during different developmental stages of four different sweet cherry cultivars. The correlation between the dynamic changes of sugar and acid during fruit development was analyzed.【Results】The results indicated that glucose, fructose and sorbitol were the major soluble sugar components of all four sweet cherry cultivars, and the level of glucose was the highest in all tested cultivars while the sorbitol was the lowest. the change tendency of the contents of total sugar and components were basically similar in four different sweet cherry cultivars. It increased constantly during fruit development. The total sugar and sugar components of four sweet cherry cultivars entered a rapid accumulation period from 22th day after flowering. The total sugar accumulation began to slow down from 28th day after flowering in early ripening varieties Крупноплодная and Zaomilu, while which began to slow down on the 40th days after flowering in medium- repening varieties Caihong and Linglongcui, and the soluble sugar content of all four sweet cherry cultivars reached the highest at fruit ripening. In mature fruits, the total sugar content of medium-repening varieties Caihong and Linglongcui was significantly higher than that of early-repening varieties Крупноплодная and Zaomilu. According to the components and content of organic acid in four sweet cherry cultivars, the major organic acid was malic acid, followed by tartaric acid and then citric acid. The level of acetic acid, oxalic acid, shikimic acid and fumaric acid were all very low and it had significantly different change patterns during fruit development. The oxalic acid decreased to zero in all of four different sweet cherry cultivars during fruit ripening. During fruit development, the change of total acid and malic acid was completely similar in different cultivars. The content of malic acid had a stable accumulation period in the early stage of fruit development in four different varieties, and began to increase rapidly after 22 days of flowering, slowed down after 28 days of flowering. The total acid and malic acid content of high acidity varieties Крупноплодная and Caihong showed a continuous upward trend during the whole fruit development process, while it showed a trend of decreasing first and then increasing in low acidity varieties Zaomilu and Linglongcui. The tartaric acid in all four varieties showed an overall upward trend and the level was lower than that of malic acid during fruit development. In the process of fruit development, the content of citric acid in Caihong and Linglongcui showed a downward trend, while it showed an upward trend in Крупноплодная and Zaomilu. The correlation analysis revealed significantly positive correlations between the three soluble sugars in the four sweet cherry fruits. The contents of three soluble sugars and malic acid were significantly and positively correlated. The contents of three soluble sugars and malic acid showed significantly or highly significantly and negatively correlations with the contents of citric acid and oxalic acid.【Conclusion】The glucose was the major sugar component of sweet cherry, and the total sugar content showed an upward tendency during the course of fruit development. The total sugar content of medium-repening varieties was significantly higher than that of early- repening varieties at fruit ripening stage. The malic acid was the main organic acid in all four sweet cherry cultivars, and the change trend of total acid content was consistent with malic acid, which showed an upward trend with fruit development. During fruit development, there were differences in the change tendency of organic acid content between high acidity varieties and low acidity varieties. The period 22 days after flowering was a key period for the internal comprehensive quality formation for sweet cherries. Therefore, it would be the key period to strengthen the management of fertilizer andwater, and meanwhile, this stage would be the key period for fruit quality regulation. When the fruit was fully ripe, the ratio of sweetness to acid from high to low was as follows: Caihong ＞ Linglongcui ＞ Zaomilu ＞ Крупноплодная.