Abstract: In this study, the solid-state fermentation process of Shanxi aged vinegar was investigated. Samples of fermented grains (Cupei) taken at different spatial locations and at different fermentation times were analyzed for physicochemical characteristics, flavor substances and microbial community composition by metagenomics and headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). The results showed that the moisture and temperature of Cupei significantly varied among spatial locations. A total of 93 volatile flavor compounds were detected during the fermentation process, and the total content of volatile compounds decreased in the order of upper layer > middle layer > lower layer. The total acid contents in the upper, middle, and lower layers were significantly negatively correlated with Proteus, Salicicolus, Staphylococcus, and Klebsiella (P < 0.05), affecting microbial growth and metabolism. The water content of the lower layer significantly affected the growth and metabolism of Proteus, Salicicolus, Saccharomyces, Staphylococcus, and Klebsiella (P < 0.05). Proteus, Saccharomyces, Staphylococcus, and Klebsiella were closely related to physicochemical indicators during the fermentation process. The growth and metabolism of Proteus, Salicicolus, Saccharomyces, Staphylococcus, and Klebsiella in the upper layer of Cupei promoted the production of esters such as ethyl linoleate and ethyl oleate, while the fermentation conditions in the middle and lower layers inhibited the production of some esters. This study helps us to comprehensively understand the brewing mechanism of Shanxi aged vinegar.

Key words: Cupei; metagenomics; microorganism; physicochemical factors; volatile flavor; correlation analysis