Abstract:To obtain soybean yoghurt with enhanced physiological activity, this study investigated the effect of soybean germination on the fermentation characteristics of soymilk by lactic acid bacteria and the physiological activity and flavor of soymilk. The results showed that within the initial 72 h, the content of trichloroacetic acid-soluble nitrogen and free amino acids in soybean significantly increased (P＜0.05) with the germination time. The fermentation characteristics of lactic acid bacteria-germinated soymilk were significantly improved, resulting in the duration to reach the fermentation endpoint (pH 4.5) shortened from 7.2 h to 5.0 h. Additionally, the titratable acidity increased from 42.18 °T to 66.56 °T, accompanied by an increase in the content of lactic acid and citric acid. Germination also reduced the hardness of lactic acid bacteria-fermented soymilk, resulting in a smoother texture. After 72 h of germination, lactic acid bacteria-fermented soymilk exhibited increased physiological activity with a 19.83 mg/hg increase in γ-aminobutyric acid content, a 115.02% increase in isoflavone glycosides, and significant enhancements in DPPH, ABTS, and hydroxyl radical scavenging rates(P<0.05). On the other hand, germination led to a noticeable increase in off-flavor compounds in soy milk. Considering the combined effect of germination on physiological activity and flavor, soybean yoghurt was prepared using soybeans germinated for 36 h. The influence of 4 direct inoculation fermentation agents on the flavor and sensory quality of soy yogurt was evaluated. The results showed that soy yogurt fermented with Agent A had the lowest content of off-flavor compounds and the best sensory quality.
