Changes in accumulation of sugars and acids in the fruits of Luxiu pear during the mid to late period of growth and development and postharvest storage

Abstract: 【Objective】Luxiu is a new variety of pear(P. pyrifolia Nakai) bred by Qingdao Agricultural University with good balance of sugars and acids and pleasant flavor. The changes of the composition and contents of the soluble sugars and organic acids of the fruits of Luxiu during the development process and storage were studied in order to explore the accumulation mode of sugars and acids of the variety and to determine the suitable time for harvest and marketing.【Methods】The soluble sugars and organic acids were determined by high performance liquid chromatography. The fruits were selected for sampling on 80 d, 100 d and 120 d(harvest time) after flowering, and the peel, middle pulp and nearcore pulp were sampled respectively. All the samples were frozen in liquid nitrogen and stored at-80 ℃.【Results】The total soluble sugars of Luxiu pear were mainly composed of fructose, glucose,sucrose and sorbitol. The sugar content in each measured part of the fruits was gradually increased from80 d to 120 d after anthesis. There was no significant difference in the change tendency of sugar content between the middle pulp and the near-core pulp at the harvest time, but sugar contents of those two parts were significantly higher than that of the peel. However, the accumulation rate of total soluble sugar of the middle pulp was significantly higher than that of the near-core pulp and higher than that of the peel. The change trends of the sugar components in the three parts of the fruits were different. The early increase was mainly related to the increase of fructose, glucose, and the contents of these three sugars reached the highest value on 100 days after anthesis. The late increase of the sugar content was mainly related to the rapid accumulation of sucrose before maturity. The content of sorbitol did not change significantly during the whole determination period. After 30 days of postharvest storage, the total soluble sugar still showed an upward trend, and then it gradually decreased. The contents of fructose and glucose had the same change trend during the storage period, both of them decreased first, reached the lowest value on 60 days of storage, then increased, and decreased again during the late storage period. The content of sorbitol was similar to those of fructose and glucose, but increased after 30 days of storage compared with that on 0 d. The change trend of sucrose content, which was different from the other three kinds of sugar, increased continuously after harvest, reached the highest value on 60 days, then decreased. The organic acids of Luxiu pear fruits were mainly composed of malic acid, citric acid, tartaric acid and quinic acid. On the whole, the content of malic acid was higher than those of citric acid and other organic acids, so it could be considered as the dominant acid. The change of total organic acid content was consistent with that of malic acid, which decreased with the growth and ripening of the fruits.Although the citric acid content increased with the development of the fruits, it was always lower than that of the malic acid. The content of organic acids of the peel was lower than those of the pulp and near-core part. The changes of organic acid content of middle pulp and the near-core pulp was similar,which decreased significantly on 100 d after anthesis and kept this level until harvest. At the early stage of storage, the content of organic acids continued to decrease, and reached the lowest value on 60 d.The contents of malic acid and oxalic acid decreased at early storage and reached the lowest value on30 d and 60 d of storage respectively. The contents of citric acid, quinic acid and shikimic acid did not change significantly during storage.【Conclusion】The contents of fructose, glucose and sorbitol of the Luxiu pear fruits were relatively higher in mid-development stage and late storage time, while the contents of sucrose of the fruits were relatively higher during harvest and early storage time. The content of malic acid was always higher than that of citric acid during the whole tested period. The fructose, sucrose and malic acid might be the main contributing factors to the special flavor of the Luxiu pear fruits.