Changes in quality components and antioxidant activity of peony seed soy sauce during low‐salt solid‐state fermentation

Abstract BACKGROUND In this study, the fermentation conditions of peony seed soy sauce (PSSS) koji were optimized by response surface method, and the quality components and antioxidant activity of PSSS were investigated at different low‐salt solid‐state fermentation stages. RESULTS Results of response surface method showed that the optimal fermentation conditions were 460.6 g kg −1 water content, 48.6 h culture time, 31.5 °C culture temperature and ratio 2.1:1 (w/w) of peony seed meal:wheat bran, with the highest neutral protease activity (2193.78 U g −1 ) of PSSS koji. PSSS had the highest amino acid nitrogen (7.69 g L −1 ), salt‐free soluble solids (185.26 g L −1 ), total free amino acids (49.03 g L −1 ), essential free amino acids (19.58 g L −1 ) and umami free amino acids (16.64 g L −1 ) at 20 days of fermentation. The highest total phenolics were 5.414 g gallic acid equivalent L −1 and total flavonoids 0.617 g rutin equivalent L −1 , as well as the highest DPPH radical scavenging activity (86.19%) and reducing power (0.8802, A 700 ) of PSSS fermented at 30 days. Sensory evaluation showed that fermentation of 20 days and 25 days could produce a better taste and aroma of PSSS than 15 days and 30 days. CONCLUSION PSSS had the highest quality components in the middle of fermentation (20 days) and the highest antioxidant activity in the late fermentation period (30 days). These results demonstrated that peony seed meal could be used to produce high‐quality soy sauce with high antioxidant activity. © 2023 Society of Chemical Industry.