Microbiomics and flavoromics insights into the effect of high temperature steam pretreatment on the flavor of walnut meal-based soy sauce

Walnut, the world's most cultivated oilseed tree, produces protein-rich meal after oil extraction, offering a promising plant protein source, though its efficient utilization remains challenging. This study employed high throughput sequencing and flavoromics to evaluate the effects of high temperature steam pretreatment (HTSP) on the flavor and microbial composition of walnut meal soy sauce (WMSS). HTSP increased the total nitrogen (1.10 g/100 g), amino acid nitrogen (1.46 g/100 g), and titratable acidity (0.77 g/100 g) in WMSS. During fermentation, Aspergillus and Enterobacter were the dominant microorganisms, while Weissella , Acinetobacter , Lactobacillus , and Rhodotorula showed substantial growth after HTSP. A total of 383 non-volatile compounds and 56 volatile compounds were identified by LC-MS and GC-IMS respectively. Among these, the relative contents of esters (4.31 %) and furans (2.23 %) were found to be increased following HTSP. Pathway analysis revealed that the alanine, aspartic acid and glutamic acid metabolism was most strongly expressed on the 16th day, which was closely related to the formation of umami. This study provides insights into the impact of HTSP on the flavor and microbial composition of WMSS.