Enhancement of Antioxidant and Phenolic Properties of Soy Whey By-Product Through Aspergillus oryzae Fermentation

Abstract

Despite being considered as a waste by-product, soy whey possesses a considerable amount of organic compounds that could still be further utilized through microbial fermentation with Aspergillus oryzae. The objective of this study was to assess the effect of glucose supplementation on the physicochemical properties including pH, °Brix, viscosity, total phenolic content (TPC), total flavonoid content (TFC), and antioxidant capacity of soy whey fermented using Aspergillus oryzae. The fermentation was conducted under static conditions for 72 hours using different glucose concentrations (0%, 1%, 3%, and 5% w/v). Antioxidant activity was determined using the DPPH radical scavenging, while TPC and TFC were quantified using the Folin–Ciocalteu and aluminum chloride assays. Glucose supplementation significantly increased °Brix values (1.00 ± 1.10 to 5.56 ± 0.53) and pH, while viscosity remained unchanged (3.12–3.78 cP). The highest TPC and TFC values were obtained at 5% glucose supplementation, reaching 179.32 ± 6.98 mg GAE/L and 20.25 ± 1.70 mg QE/L, respectively. Antioxidant activity also improved with increasing glucose concentration, as indicated by a decrease in IC50 values from 330.97 ± 23.65 mg/L in the raw soy whey to 159.77 ± 13.10 mg/L in the 5% treatment. These findings indicate that glucose supplementation, particularly at 5%, provides favorable conditions for A. oryzae metabolism.