Abstract: The objective of this study was to investigate the effects of wheat germ on physicochemical properties and antioxidant activities of Chinese traditional high-salt diluted soy sauce made with soybean, flour and wheat germ. Antioxidant activities of the raw materials, koji and soy sauce were evaluated by Fe3+ reducing power, 1,1-diphenyl-2-picryhydrazyl (DPPH) radical scavenging, 3-ethylbenzthiazoline-6-sulphonate ABTS radical scavenging and oxygen radical absorbance capacity (ORAC) assays. Meanwhile, correlation analysis between bioactive components and antioxidant capacity of soy sauce was carried out. The results showed that wheat germ could significantly improve the contents of total nitrogen, amino nitrogen, total phenols, total flavonoids and Maillard reaction products in soy sauce (P < 0.05). The antioxidant activity of soy sauce could be improved by using wheat germ and increased with fermentation time. Besides, sample 2 (S2, soybean/flour/wheat germ ratio = 7:1:2) had the highest antioxidant activity, which was significantly higher than that of the control group (S1) (P < 0.05). The greater the amount of wheat germ added, the higher antioxidant capacity of the raw materials and koji, while the antioxidant capacity of soy sauce increased firstly and then decreased. The antioxidant activity of soy sauce was significantly positively correlated with total phenols content and Maillard reaction products (P < 0.01, r > 0.8), so that both of them could be inferred as main antioxidant substances in soy sauce. However, total flavonoid content was not highly correlated with DPPH radical scavenging capacity, ABTS radical scavenging capacity, Fe3+ reducing power and ORAC (r = 0.292, 0.446, 0.703, and 0.397), and so it could not be used to evaluate the antioxidant activity of soy sauce. In conclusion, soy sauce quality and its antioxidant activity can be improved by partial replacement of wheat germ for flour.

Key words: wheat germ, soy sauce, quality, active components, antioxidant capacity