Abstract: Soy whey is a major by-product from the soy product industry, which is suitable for the growth of microorganisms due to rich nutrients. Kombucha is a sweet and sour functional beverage made from sweet black tea fermented by a symbiotic?consortium of yeasts and acetic acid bacteria. In this study, we used soy whey as a new fermentation substrate for kombucha consortium to develop a novel functional beverage. The results demonstrated that after fermentation for 6 days, pH decreased to 3.24, which corresponded to an increase in total titration acidity up to 0.121 mol/L, and the content of reducing sugar decreased to 1.37 mg/mL. Total flavonoids from unfermented and fermented soy whey were extracted using 80% methanol and were qualitatively and quantitatively determined by high performance liquid chromatography (HPLC). Their antioxidant capacity was evaluated by 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and 2,2’-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) cation radical scavenging ability, ferric reducing antioxidant power and reducing power. The results showed that the total flavonoids concentration of 6-day fermented soy whey was up to 268.45 mg/L; the soybean isoflavonoids glycoside concentration was reduced to 49.76 mg/mL, and the soybean isoflavonoids aglycone concentration was increased to 150.95 mg/mL compared with the unfermented one. The fermentation could significantly improve the antioxidant activity of soy whey. This study provides a new way of utilizing soy whey resource.

Key words: kombucha, soy whey, total flavonoids, soybean isoflavones, in vitro antioxidant activities