Flavor formation by amino acid catabolism in low-salt sufu paste, a Chinese fermented soybean food

Abstract

In this study, the low-salt sufu paste was fermented enhanced by a mixed starter (Pichia fermentans, Kodamaea ohmeri and Lactococcus lactis subsp.) and α-ketoglutarate. Multispecies microbial community is crucial for the flavor formation of sufu paste during post-ripening. Consequently, the primary biochemical pathways of the flavor formation were analyzed using a metagenomic approach in conjunction with gas chromatography mass spectrometry (GC-MS). After post-ripening for 15 d, a total of 86 volatile flavor compounds (VFCs) were tentatively identified, in which 6 compounds were recognized as the main characteristic VFCs. The metagenomics revealed that Actinomucor elegans, Lactobacillus fermentum, Lactococcus lactis subsp., Pichia fermentans, Lactobacillus delbrueckii and Propionibacterium acidipropionici were the dominant species. According to the functional annotation, amino acid metabolisms were identified as the predominant pathways for flavor formation. Among them, aromatic amino acids metabolisms accounted for the highest proportion, up to 41.3%. The VFCs formation pathways mainly involved transamination, decarboxylation, dehydrogenation and oxidation reaction. The amino acid transamination was proposed as a crucial step in VFCs formation, and the corresponding aminotransferases were the key rate-limiting enzymes. These findings have implications for enhancing the flavor quality of sufu paste and elucidating the mechanism of flavor formation in traditional soybean fermented food.