关键词: 鸭梨, 品质, 挥发性物质, 电子鼻, 乙烯, 基因表达

Abstract:

【Objective】The aim of this study was to compare the differences of fruit quality, respiration rate, ethylene production rate, electronic nose characteristics, volatile compounds and related gene expression in Yali pear between cold and cellar storage, and to further analyze the effects of two storage methods on the formation of aroma substances and its mechanism. 【Method】Postharvest Yali pear was stored in cold and cellar condition, and the fruit firmness, soluble solids content (SSC), titratable acid (TA) content, respiration rate and ethylene production rate were measured. The changes of volatile compounds during storage were measured by electronic nose, and the components and contents of volatile substances were determined by GC-MS. The expression of genes related to ethylene biosynthesis (PbACS1 and PbACO2), signal transduction (PbETR1, PbETR2, PbERS1a, PbERS1b, PbEIN3 and PbERF) and volatile compound synthesis (PbAAT1, PbADH2, PbADH3, PbADH5, PbHPL, PbLOX1 and PbLOX8) was analyzed by real-time PCR. 【Result】During cold storage of Yali pear fruit, the firmness had no obvious variation, and the SSC increased, while the TA content decreased. During cellar storage, there was a remarkable decrement in firmness and increment in TA content, but there was no obvious variation in SSC. Compared with cold storage, the respiration rate was higher and the peak of ethylene production rate appeared one month earlier under cellar storage. The results showed that the electronic nose could effectively distinguish the volatile compounds of Yali pear in different storage methods. Four sensors, including W1W, W5S, W2W and W1S, played the critical role in the identification of volatile compounds, and there were more volatile substances in cellar storage. The volatile compounds, such as aldehydes, esters, alcohols, terpenes, alkanes, etc, were found in the peel and flesh of Yali pear, and which contents were higher in peel than that in flesh. 36, 33 and 28, 24 kinds of volatile compounds were detected in peel and flesh of fruit under celler, cold storage, respectively. There were more ester compounds in cellar storage than those in cold one, among which, ethyl caproate, ethyl octanoate, ethyl butyrate, (E, Z) 2,4-decadiene ester were the main aroma substances in the peel, ethyl caproate and ethyl butyrate were the main aroma substances in flesh. The analysis on expression of genes related to ethylene and aroma compound synthesis showed that the expression of ACC oxidase (PbACO2), lipoxygenase (PbLOX1) and alcohol acyltransferase (PbAAT1) genes were significantly increased, and the expression of ethylene insensitive transcriptional regulator gene (PbEIN3) was down regulated in cellar storage in contrast to cold storage. 【Conclusion】Compared with cold storage, cellar storage condition promoted ethylene production and the expression of genes related to ethylene biosynthesis (PbACO2) and aroma compound synthesis (PbLOX1 and PbAAT1), thus, made more kinds and contents of aroma substances, and exhibited more rich aroma in Yali pear.

Key words: Yali pear, quality, volatile compound, electronic nose, ethylene, gene expression