Effects of bagging on free amino acid and hydrolyzed amino acid contents in fruit of Pyrus bretschneideri‘Yali’

Abstract:【Objective】As an important practice in pear production, fruit bagging effectively reducespesticide residues, prevents the invasion of diseases and pests, improves the appearance and thus commercialvalue of fruits.‘Yali’(Pyrus bretschneideri) pear, an ancient variety native to Hebei province,China, is rich in nutrients and popular among consumers. Amino acids are important components offruit quality, playing a vital role in fruit development. The dynamic changes in free amino acids and hydrolyzedamino acids during the development of fruit with or without bagging treatment have not beenreported. The purpose of this study is to investigate the impact of fruit bagging treatment on free aminoacids and hydrolyzed amino acids in‘Yali’【. Methods】The experiment was carried out in 2018 in the Jiangpuexperimental orchard, belonging to the College of Horticulture, Nanjing Agricultural University.The‘Yali’trees were 10- year- old planted at a space of 5 m × 5.5 m. At 36 days after full bloom (DAFB), 30 young fruit in each tree were bagged with double-layer paper bags, which were yellow outsideand black inside, and a total of 600 fruit were bagged in 20 trees. The un-bagged fruit were used asthe control (CK). Only one fruit per inflorescence was bagged, and the rest fruit in the same inflorescencewere removed to reduced nutrient waste. The paper bags were removed until commercial harvest(September 5th). 100- 120 fruit (including treatment and control) were collected at the early stage offruit expansion (36 DAFB), the rapid expansion stage (81 DAFB), the late stage of fruit expansion (110DAFB), the nutrient accumulation stage (145 DAFB) and the mature stage (160 DAFB). At each samplingtime, the sampled fruit were randomly divided into three replications. The pit and seeds were removedimmediately after harvesting, and the peel and pulp tissues were separately crushed in liquid nitrogen,and then stored in a freezer at -80℃ before determination of amino acids. The composition andcontents of free amino acids and hydrolyzed amino acids in‘Yali’fruit were analyzed with an L-8900automatic amino acid analyzer (Hitachi, Japan). Excel 2013 and IBM SPSS Statistics 25.0 were appliedfor data analysis. 【Results】17 amino acids were determined during fruit development of‘Yali’pear, includingaspartic acid (Asp), threonine (Thr), serine (Ser), glutamate (Glu), glycine (Gly), alanine (Ala),cysteine (Cys), valine (Val), methionine (Met), isoleucine (Ile), leucine (Leu), tyrosine (Tyr), phenylalanine(Phe), lysine (Lys), histidine (His), arginine (Arg) and proline (Pro). The compositions of free aminoacids and hydrolyzed amino acids were distinct between the peel and the pulp during fruit development.Total content of free amino acids in the peel and the pulp increased during fruit development,while hydrolyzed amino acids decreased. Bagging treatment altered the content of free amino acids andhydrolyzed amino acids. At mature stage (160 DAFB), total content of free amino acids in the peel ofbagged fruit were significantly higher than in that of the control (p ＜ 0.01). However, the total contentof free amino acids in the pulp was significantly lower than that of the control (p ＜ 0.05). On the otherhand, total content of hydrolyzed amino acids in the peel of the bagged fruit were significantly lowerthan that of the control (p ＜ 0.05), while there was no significantly difference in total content of hydrolyzedamino acids in the pulp between bagged fruit and the control. 【Conclusion】During‘Yali’fruit development,the content of total hydrolyzed amino acids decreased, while free amino acids increased.Bagging treatment, although did not change their expression patterns, altered the contents of free aminoacids and hydrolyzed amino acids during fruit development. When fruit came into mature stage, a lowerabundance of hydrolyzed amino acids and a higher content of free amino acids were detected in the peelof the bagged fruit, while a reverse phenomenon was observed in the pulp of fruit.