Effect of pasteurization process and fermentation time on physico-chemical properties, antioxidant capacity and total phenolic content of tempeh-based soy sauce

Tempeh can be processed into soy sauce to enhance its functional value. The sauce must go through a pasteurization process that may impact its qualities. Therefore, this study aims to determine the effect of pasteurization (70℃ for 15 min) and fermentation time (up to 4 d) on the physico-chemical properties, antioxidant capacity and total phenolic content of tempeh-based soy sauce. The soy sauce was produced through moromi fermentation lasting up to 8 weeks, with tempeh fermentation periods 2, 3 and 4 d tested alongside koji as the control. Results indicated that pasteurization and fermentation time significantly increased the antioxidant capacity (EC50) of tempeh-based soy sauce up to 1.91±0.18 mg soy sauce/mL (p<0.05). Total phenolic content significantly decreased to 897±3 µg gallic acid equivalent.mL-1 after pasteurization, while the fermentation time significantly increased total phenolic content (p<0.05). The total dissolved solids and total soluble protein increased with the fermentation time (p<0.05). The L*, a*, b* and the total soluble protein decreased after pasteurization (p<0.05). Consequently, fermentation time positively affected the physico-chemical characteristics, total phenolic content and antioxidant capacity of tempeh-based soy sauce, while pasteurization increased the antioxidant capacity and darkened the color of the soy sauce but decreased total phenolic content.