Application of high-temperature steam pretreatment of rapeseed meal in soy sauce fermentation: dynamic evolution of taste, aroma, and microbial communities

Rapeseed meal is rich in protein, but its high-value utilization remains insufficient. In this study, high-temperature steam pretreatment (HTSP) was applied to rapeseed meal to reduce safety- and flavor-limiting factors and improve its suitability as a raw material for soy sauce fermentation. Compared with the CON group, HTSP significantly reduced the contents of glucosinolates, isothiocyanates, erucic acid, and phenolic-related compounds in rapeseed meal, with glucosinolates and isothiocyanates decreasing by 59.02% and 92.65%, respectively. Meanwhile, the contents of protein, soluble protein, and reducing sugars increased to 39.28, 16.42, and 1.18 g/100 g, corresponding to 1.11-, 2.01-, and 1.97-fold those of the CON group, respectively. Subsequently, HTSP-treated rapeseed meal was used as the main raw material for soy sauce fermentation. During the 1–15 d fermentation period, the sample fermented for 15 d showed the most favorable physicochemical and flavor characteristics. At this stage, the contents of total nitrogen, amino acid nitrogen, reducing sugars, total acidity, and soluble solids reached 1.16, 0.70, 2.13, 1.22, and 34.31 g/100 mL, corresponding to 4.30-, 3.33-, 3.23-, 30.50-, and 4.73-fold those on day 1, respectively. During fermentation, the taste profile shifted from bitterness and sourness toward sweetness and umami, while the aroma profile evolved from fruity notes to nutty, roasted, and floral notes. Correlation analysis indicated that Weissella and Zygosaccharomyces rouxii were important microbial taxa closely associated with the quality and flavor development of rapeseed meal soy sauce, and may contribute to the accumulation of taste compounds in the early stage and aroma formation in the middle and late stages, respectively. Overall, HTSP effectively enhanced the utilization potential of rapeseed meal as a fermentation substrate, supporting its high-value application in soy sauce brewing.