Utilization of propionic acid bacteria in the biotransformation of soy (tofu) whey: Growth and metabolite changes.

Soy whey, a by-product from the tofu and soy protein isolate industry was evaluated as a substrate for a biofortified beverage using several propionic acid bacteria (PAB). PAB growth and changes in sugars, organic acids, amino acids and isoflavones were investigated. Vitamin B12 and short-chain fatty acid (SCFA) production were measured over time. Acidipropionibacterium acidipropionici (DSM 20272) showed the highest growth, compared to the other three PABs (Propionibacterium freudenreichii [DSM 20271 and DSM 4902], A. jensenii [DSM 20535]). Acidipropionibacterium (DSM 20272 and DSM 20535) showed the best propionic acid and acetic acid production, while P. freudenreichii produced the most succinic acid. Propionibacterium freudenreichii exhibited significant vitamin B12 production at 4.06 ± 0.28 µg/L for DSM 20271, followed by 2.58 ± 0.22 µg/L for DSM 4902. Notably, all PAB displayed strong ß-glycosidase activities evidenced by the conversion of isoflavone glycosides to isoflavone aglycones. The stark differences between Acidipropionibacterium spp. and Propionibacterium spp. indicate that the former PAB is specialized in SCFA production, while the latter PAB is better at vitamin B12 bioenrichment. This study demonstrated the possibility of employing PAB fermentation to improve SCFA and vitamin B12 content. This can open avenues for a beverage or functional ingredient development.