Differential Analysis of Key Flavor Substances in the Fermentation Process of Green Capsicum frutescens

In order to investigate the pattern of volatile flavor compounds changes during the fermentation of green Capsicum frutescens, samples from five different fermentation stages (0, 6, 12, 18 and 23 d) were analyzed by using solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) with partial least squares discriminant analysis (PLS-DA), cluster analysis (CA), and relative odor activity value (ROAV). The results showed that 88, 84, 82, 90 and 93 volatile flavor compounds were detected at each fermentation stage. A total of 35 potentially different compounds (VIP>1) were screened by PLS-DA and variable importance in projection (VIP), and the different characteristic flavor substances increased significantly in the later stages of fermentation (18 d and 23 d). The results of ROAV and UpSet plots showed that 8, 8, 10, 7 and 9 key flavours were detected in the five fermentation stages of green Capsicum frutescens (ROAV>1), respectively. Hexanal, nonanal, octanal and decanal were the key flavours unique to the 0 d of fermentation, while 2-heptanol, ethyl palmitate and 4-ethyl guaiacol were the key flavours for the middle and late stages of fermentation (12, 18 and 23 d). 4-Ethylguaiacol was the key flavour at 23 d, providing a unique fermentation pungent aroma to the fermented green Capsicum frutescens. This study revealed the differences in volatile flavour components and key characteristic aroma components in different fermentation stages of green Capsicum frutescens, and provided theoretical basis for the subsequent development of green Capsicum frutescens products based on volatile flavour substances as well as the regulation of flavour quality in the fermentation process.