Dynamics of physicochemical properties, volatile aroma compounds and non-volatile metabolites of Zhaiji millet vinegar during aging: A systematic elucidation by GC-IMS coupled with UPLC-MS/MS untargeted metabolomics

Zhaiji millet vinegar (ZJMV) is a traditional grain-fermented condiment whose quality improvement is associated with aging time. This study revealed the evolution of physicochemical properties and whole-component of ZJMVs aging 2 to 10 years. Results demonstrated pH, chroma, and the content of total acid, reducing sugar, and amino acid nitrogen fluctuate dynamically, while antioxidant activities were significantly correlated with the content of total flavonoids, total phenols, tetramethylpyrazine, amino acids, and organic acids ( p  < 0.05). GC-IMS and metabolomics identified 47 volatile organic compounds (VOCs) and 6530 metabolites, with 6 differential VOCs and 19 differential metabolites ( p  < 0.05, variable importance in projection (VIP) > 1, fold change (FC) < 0.5 or > 2) being shared aging markers. KEGG pathway analysis indicated amino acid metabolism enriched the most differential metabolites, whereas biosynthesis of various alkaloids was critical. Our findings provide novel mechanistic insights into the quality development of ZJMV during aging.