Characterization of chemical properties and components conversion during the fermentation of Semen Sojae Praeparatum.

Semen Sojae Praeparatum (SSP) is traditional dual-purpose product with both medicinal and edible applications. In this study, electronic nose, comprehensive two-dimensional gas chromatography-mass spectrometry, and ultra-performance liquid chromatography were employed to characterize the fermentation-associated attributes underlying "distinct aroma and umami-rich taste" and to analyze the dynamic isoflavones changes. Results revealed that moisture content and reducing sugars initially increased and subsequently decreased, while pH declined during pre-fermentation and remained stable thereafter. Key flavor contributors were identified as acids, aldehydes, alcohols, esters, and pyrazines, specifically 2-furanmethanol, furfural, 2,5-dimethylpyrazine, isovaleric acid, benzaldehyde, and acetic acid, which collectively defined the characteristic aroma profile. Free amino acids, metabolized from proteins by protease, accumulated mainly during pre-fermentation. Isoflavone aglycones gradually increased due to the deglycosylation of glycosides in the pre-fermentation phase, whereas both aglycones and glycosides remained stable during post-fermentation. These findings establish a scientific foundation for understanding the fermentation mechanisms of SSP.