Abstract: The application of Zygosaccharomyces rouxii in conjunction with Aspergillus spp. was proposed to ferment soy sauce with rice dreg protein as a substrate. The effect of Z. rouxii on the flavor and antioxidant activity of soy sauce was evaluated. Results revealed that co-fermentation with Z. rouxii significantly improved the contents of glutamic acid, 2-ethyl-4-hydroxy-5-methyl-3(2H)-furanone and 4-vinylguaiacol, and antioxidant activities in vitro such as reducing power, 1,1-diphenyl-2-picrylhydrazyl (DPPH) and hydroxyl free radical scavenging capacity and total antioxidant capacity (trolox equivalent antioxidant capacity, TEAC) in soy sauce. The best quality of soy sauce was obtained by inoculating 0.025% of Z. rouxii when Aspergillus spp. fermentation reached pH 5.0. After 45 days of fermentation, the contents of total amino acids and antioxidant amino acid increased by 24.76% and 40.73%, respectively compared with the soy sauce without Z. rouxii fermentation, and the reducing power was 5 830.43 μg VC/mL. Furthermore, obvious DPPH radical scavenging activity was detected in volatile oils, pigments and retenate with molecular mass less than 10 kDa from the soy sauce produced by co-fermentation, which was concentration dependent.

Key words: Zygosaccharomyces rouxii, Aspergillus oryzae, Aspergillus niger, rice dreg, amino acid nitrogen, flavor, antioxidant activity