Di Gong _ College of Food Science and Engineering, Gansu Agricultural University, Lanzhou, 730070, China.
Yang Bi _ College of Food Science and Engineering, Gansu Agricultural University, Lanzhou, 730070, China.
Yuanyuan Zong _ College of Food Science and Engineering, Gansu Agricultural University, Lanzhou, 730070, China. 
Yongcai Li _ College of Food Science and Engineering, Gansu Agricultural University, Lanzhou, 730070, China.
Edward Sionov _ Department of Postharvest Science of Fresh Produce, Agricultural Research Organization, The Volcani Center, Bet Dagan, 50250, Israel.
Dov Prusky _ College of Food Science and Engineering, Gansu Agricultural University, Lanzhou, 730070, China; Department of Postharvest Science of Fresh Produce, Agricultural Research Organization, The Volcani Center, Bet Dagan, 50250, Israel.

Amino acids (AAs) play a critical role in resistance response and biosynthesis of volatile compounds (VOCs) in fruit. In this study, we inoculated apple fruits (cv. Delicious) with Penicillium expansum to investigate the effect of different AA accumulation on the biosynthesis of branched-chain VOCs at different stages of colonization. Generally, infection significantly increased the total AAs in fruit by 38.65 %. Of the 17 AAs detected in fruit, the contents of Asp, Val, Leu, Ala, Ser, Cys, Thr, His, Agr, Glu, Met, Gly, and Pro increased in the early and middle stages of colonization (< 6 DAI), while Ile, Lys, Phe and Tyr increased at the late stages (> 6 DAI). Moreover, infection promoted higher activities of PDC and PDH involved in branched-chain VOCs biosynthesis, leading to increased contents of branched-chain VOCs. These results suggest that P. expansum increases AA’s accumulation and release of branched-chain VOCs in apple fruit.