Growth, Substrate, and Metabolite Changes of Probiotic Bifidobacterium animalis subsp. lactis in Soy (Tofu) Whey

Abstract

Soy (tofu) whey is one of the two side-streams from tofu processing, which has been shown to be suitable for microbial growth. In this work, probiotic Bifidobacterium animalis subsp. lactis Bl-04 and B94 were used to ferment soy whey with different supplements to explore the possibility of harnessing Bifidobacterium fermentation to upcycle soy whey. Soy whey was supplemented with different supplements (control, CN; glucose, G; glucose + cysteine, GC; glucose + cysteine + yeast extract, GCY) and inoculated with either B. lactis Bl-04 or B94. Growth, substrate utilization, and metabolic products were monitored before and after fermentation. Bl-04 managed to grow in all four media, while B94 needed cysteine to grow. The contents of sucrose, cysteine, methionine, and succinic acid decreased in the fermented samples. Acetic and lactic acids were produced in fermented soy whey ranging from 0.49–2.66 g/L and 0.58–2.88 g/L, respectively, with vitamin B12 at 2.06–4.56 μg/L. Increases in isoflavone aglycones (0.19–25.05 mg/L) and iron (0.03–0.12 mg/L) were observed. The PCA analysis of volatiles showed a distinct clustering due to short-chain fatty acids (acetic, butyric, and isovaleric acid), 2,3-butanedione (diacetyl), H2S, and 3-methylthiophene. Overall, the selection of suitable bifidobacterial strains and supplements for soy whey fermentation can open avenues to upcycle soy whey.