Enhancement of the organic acid content and antioxidant capacity of yellow whey through fermentation with Lacticaseibacillus casei YQ336

Fermentation is considered an effective tool for improving the functional characteristics of food. In this study, Lacticaseibacillus casei YQ336 was used to ferment yellow whey, and physical and chemical analysis was performed to identify the changes in the nutritional components and antioxidant activity of the fermented yellow whey. Non-targeted metabolomics was used to study the transformation of small molecular substances in the fermented yellow whey. After 48 h of pure culture fermentation with L. casei YQ336, the pH of yellow whey decreased significantly (p < 0.05). Meanwhile, the content of total acids, organic acids, sugars, total phenols, and total flavonoids and the antioxidant activity showed a significant increase (p < 0.05). A total of 628 differential metabolites were identified between fermented and unfermented yellow whey samples, of which 293 were upregulated and 335 were downregulated. After fermentation, due to the growth and metabolic activity of L. casei YQ336, meaningful metabolites such as homovanillic acid, lactic acid, oxalic acid, L-glutamic acid, and phenylalanine, as well as phenyllactic acid, gallic acid, and genistein were produced. This increased the organic acid content and antioxidant activity of yellow whey. The findings provide a theoretical and practical basis for further research on the bio-functional activity of yellow whey and the recycling and utilization of food by-products.

Effects of lactic acid bacteria fermented yellow whey on the protein coagulation and isoflavones distribution in soymilk

This study investigated the soymilk coagulation induced by fermented yellow whey (FYW), which is extensively used as a natural tofu coagulant in China. The aggregations involving proteins and isoflavone particles caused by FYW were analyzed using the proteomic technology and high-performance liquid chromatography, respectively. As indicated, the FYW-induced coagulation of soy proteins mainly occurred at pH 5.80-5.90. When the pH of soymilk decreased, the 7S β, 11S A3 and some of 11S A1a subunits and SBP, Bd, lectin and TA aggregated the earliest, and later did the 11S A4, other 11S A1a, 11S A2 and 11S A1b subunits. The 7S α and α' subunits and TB showed an obvious delay in aggregation. Moreover, isoflavones in the form of aglycones were more likely to coprecipitate with proteins, compared with glycosides. These results could provide an important reference and assistance for future research on the development of traditional FYW-tofu.