关键词: 库尔勒香梨, 脱萼果, 宿萼果, 果实品质, 挥发性代谢物, 气相色谱-质谱联用

Abstract: The commodity value of Korla fragrant pear was directly affected by its fruit quality, and studies had shown that 5-aminolevulinic acid (5-ALA) could improve fruit quality and increase the content of volatile metabolites. Therefore, in this study, different concentrations of 5-ALA (50, 100, 150, 200 mg·L-1) was applied during the fruit swelling period, and the fruit quality of decalyx fruit and persistent calyx fruit at maturity stage was determined, meanwhile, the fruit quality under 5-ALA treatment was comprehensively evaluated based on principal component analysis, and the concentration with the best effect on fruit quality improvement was screened out, and its effect on the volatile metabolites of Korla fragrant pear was discussed. The results showed that exogenous spraying of 150 mg·L-1 5-ALA had the best effect on improving the quality of fragrant pear fruit. Compared with the control, the hardness, stone cell content and titratable acid content of calyx fruit decreased significantly by 15.54%, 45.00% and 73.33%, respectively, while the soluble solids and solid acid ratio increased by 9.95% and 90.53%, respectively. At the same time, the hardness, titratable acid and stone cell content of persistent calyx fruit decreased significantly by 14.79%, 94.12% and 43.18% compared with the control, while the soluble solids, soluble sugar and solid acid ratio increased by 19.33%, 23.51% and 131.63% respectively compared with the control. In addition, the application of 5-ALA significantly increased the mass fraction of volatile metabolites in decalyx fruit and persistent calyx fruit, mainly increased terpenoids, esters and other compounds, and enriched the related aroma attributes such as wood flavor, fruit flavor, vanilla flavor, fresh flavor, grass flavor and sweetness of fruit, and was the most enriched in sesquiterpene and triterpenoid biosynthesis pathways. Among them, α-farnesene, 4-[ ( ( 1E ) -1,5-dimethyl-1,4-hexanedi-1-yl ]-1-methyl-cyclohexene, δ-cadinene, (E)-1-methyl-4-(6-methylhept-5-en-2-ylidene) cyclohex-1-ene and germacrene B annotated in this pathway were the key compounds, which were the special flavors of Korla fragrant pear, limon, citrus, lemon and soil. It was found that exogenous spraying of 5-ALA had a significant effect on improving the fruit quality of Korla fragrant pear, and the effect of applying 150 mg·L?1 5-ALA was the best, which had a significant effect on improving the content of volatile metabolites and helped to improve the aroma of Korla fragrant pear.

Key words: Korla fragrant pear, Decapitated fruit, Sedum fruit, Fruit quality, Volatile metabolites, Gas chromatography-mass spectrometry