Changes in free fatty acid and free amino acid contents in fruit of Pyrus sinkiangensis ‘Kuerle Xiangli' by bagging

Abstract:【Objective】Fatty acids and amino acids play an important role in quality formation of fruits.Bagging is an effective method of improving fruit appearance and decreasing pesticide/fungicides residues, and the physic barrier of the bag also provides protection of the fruits against damages from hail and sunburn and the attack of insects and birds. P. sinkiangensis‘Kuerle Xiangli'is one of the characteristic and economically important fruit trees in Xinjiang Uighur autonomous region, China. Fruit bagging in pear production has long been practiced widely in China for international market. However, there is no report on the influence of bagging on fatty acid and amino acid in fruit of‘Kuerle Xiangli'. The purpose of this study is to explore the changes of fatty acid and amino acid contents in fruit of‘Kuerle Xiangli'and the influence of bagging treatment with different materials.【Methods】Trials were carried out during the 2013 growing seasons on‘Kuerle Xiangli'growing in an orchard of Shayidong Farm, Xinjiang Uighur autono-mous region, China. Trees with dispersal stratified training were planted at a space of 5m × 5.5 m in 1993 and the orchard was managed based on normal commercial practice with open pollination. At 30 days after full bloom(DAFB), the young fruit of‘Kuerle Xiangli'were bagged with purple plastic film bag or single-layer white paper bag(Kobayashi NK-15, Japan). Non-bagged fruit were used as the control. Bagged fruit were the third or the fourth ordinal position of inflorescence in the upper periphery of the tree crown.The experiment was conducted using complete randomized design, and each of the selected inflorescences had only one bagged fruit. The bagged fruit were not debagged until commercial harvest(7 September).25-30 fruit were collected from each treatment at 30, 60, 90, 120, and 150 DAFB. At each sampling time,the sampled fruit were divided into three replications randomly. Free fatty acid contents were investigated by a trace gas chromatography(Thermo, USA) equipped with a flame ionization detector(FID) and a SPTM-2560 column(100 m × 0.2 mm ID, 0.20 μm). Free amino acid contents were investigated by L-8900 automatic amino acid analyzer(Hitachi, Japan). Data were generated from triplicate experiments and results were analyzed using one-way ANOVA and Duncan's multiple comparison tests. The threshold for significance was P < 0.05 or P < 0.01. The software used for statistical analysis was DPS v7.05【.Results】Five fatty acids and 15 amino acids were identified during fruit development of‘Kuerle Xiangli'. The 5 fatty acids were palmitic acid(C16∶0), stearic acid(C18∶0), oleic acid(C18∶1), linoleic acid(C18∶2) and linolenic acid(C18∶3). Among them, linoleic acid and linolenic acid were the dominant fatty acids. The 15 amino acids identified were aspartic acid(Asp), glutamic acid(Glu), glycine(Gly), alanine(Ala), cysteine(Cys), valine(Val), methionine(Met), leucine(Leu), isoleucine acid(Ile), phenylalanine(Phe), tyrosine(Tyr), lysine(Lys), histidine(His), arginine(Arg) and proline(Pro). Among of them, aspartic acid and glutamic acid were the main amino acids. Content of each free fatty acid had the similar change trend in the process of fruit development. The content of total fatty acids was highest at 60 DAFB but declined thereafter. The total content of free amino acids was high at 30 DAFB and lowest at 90 DAFB. When the fruit was ripe, the contents of linoleic acid and total fatty acids in fruit in paper bag were significantly(P < 0.05)lower than those in the control; there was no significant difference in the contents of free fatty acids between fruit bagged with plastic film bag and the control fruit. As fruit developed, the content of total amino acids decreased; the content of each amino acid was affected by bagging treatments but did not display a clear pattern. When the fruit ripened, the content of amino acid in the fruit bagged with plastic film bag was significantly higher than that in the control(P < 0.01); the content of amino acids in fruit bagged with paper bag was significantly lower than that in the control(P < 0.01).【Conclusion】In fruit of‘Kuerle Xiangli', linoleic acid, linolenic acid, aspartic acid and glutamic acid were dominant fatty acids or amino acids; the changes in fatty acid and amino acid contents during fruit development were influenced by bagging. Bagging had a greater impact on total amount of free amino acids but the influence pattern on different amino acid content was not clear. The effect of bagging on free fatty acid content was small in fruit of‘Kuerle Xiangli'. Content of each free fatty acid content had no significant difference between the bagging treatments with the two types of bagging materials(plastic film and paper). The influences of bagging on amino acids were significantly larger than those on fatty acids. The negative effect of purple plastic film bag on contents of both free fatty acids and free amino acids was smaller than that of the single-layer white paper bag.