Characteristics and upregulation of antioxidant capacity of fermented pueraria starch production wastewater with kombucha consortium

Pueraria lobata is a traditional plant used for both medicine and food. Pueraria starch has a long history of folk consumption in China. The processing of pueraria starch produces a lot of waste water and is often discarded, but it contains rich nutrients and is suitable for the growth of microorganisms. In this study, pueraria starch processing wastewater was used as a new fermentation substrate for kombucha fungus to develop a new functional beverage. After 8 days of static fermentation in 28 °C, the pH of kombucha fermented with pueraria starch processing wastewater as substrate decreased to 2.78, the total acid concentration was 0.158 mol/L, and the mass concentration of reducing sugar decreased to 2.05 mg/mL. The pueraria starch production wastewater before and after fermentation was extracted with 80% methanol and the mass concentration of total flavonoids was determined. The antioxidant activity of pueraria starch processing wastewater before and after fermentation was analyzed by using three antioxidant models: DPPH free radical scavenging ability, ABTS cationic free radical scavenging ability and ferrous ion reducing power. The results showed that after 7 days of fermentation, the mass concentration of total flavonoids in kombucha produced by the pueraria starch processing wastewater was 268.45 mg/L. The antioxidant activity of fermented kombucha beverage was significantly higher than that of unfermented pueraria starch processing wastewater. This study provides a new way for the resource utilization of Pueraria starch processing wastewater.