Background. Fermented tofu, a traditional product of Asian countries, is produced using Actinomucor elegans. The product is popularly consumed because of its unique nutrients, taste, and flavor. The fortification of tofu with purple sweet potato (PSP) can provide many health benefits, especially antioxidative properties. However, incubation conditions including temperature and relative humidity affect the growth of Actinomucor elegans, leading to changes in product quality.
Materials and methods. In this study, the effects of various temperatures (25, 30, and 35°C) and relative humidities (75, 85, and 95%) on the fermentation of tofu supplemented with PSP were carried out. The nutrient composition, including moisture, protein, lipid, ammonia, glucose, and free amino acid contents, bioactive compounds (total phenolic-TPC, total flavonoid-TFC, and anthocyanin contents), antioxidant activity in terms of DPPH and ABTS radical scavenging activities, and inhibitory activity (IC50) were monitored.
Results. The results indicate that tofu supplemented with PSP can be successfully catalyzed by Actinomucor elegans at a suitable temperature and relative humidity of 30°C and 95%, respectively. The pehtze contained 63.8% moisture, 15.36% protein, 9.43% lipid, 12.49% free amino acid, 0.05% ammonia, and 125.41 mg/g glucose. The TPC, TFC, and anthocyanin contents were 62.91 mg GAE/g d.w., 17.32 mg QE/g d.w., and 309.54 µg/g d.w., respectively. The DPPH and ABTS radical scavenging activities, and the IC50 value were 85.50 µmol TE/g d.w., 120.79 µmol TEAC/mg, and 6.61 mg/mL, respectively.
Conclusions. Fermentation at 30°C and a relative humidity of 95% produced fermented PSP tofu with high nutrition, bioactive compounds, and antioxidant activity.