A Halophilic Aromatic Yeast Coordination With Aspergillus Oryzae In Koji Making Of Soy Sauce Brewing

Soy sauce is made from fermented soybeans and wheat that are hydrolyzed by proteolytic enzymes produced from the filamentous fungus Aspergillus oryzae or Aspergillus sojae. Although industrial production overcomes the problems of seasonal production, unstable quality, and low emzyme activity in natural soy sauces, the use of pure microbial cultures in industrial koji making results in a flavour that is inferior to traditional products. This work simulated the traditional multi-strain koji making and inoculated a halophilic aromatic yeast(Zygosaccharomyces rouxii) and A. oryzae in koji making for enhancing the quality and flavor of soy sauce. The main research in this paper is listed as follows:1. A yeast survived in 20% Na Cl was selected from the soy sauce moromi and halophile and salt-tolerant yeasts. Through the strain morphologic identification and the sequence analysis of 18 S r DNA the yeast has been identified as Z. rouxii. The main aroma components of liquor are alcohols by the analysis of GC-MS, and salt has little effect on the production of aroma components.2. The effect of inoculated a halophilic aromatic yeast(Z. rouxii) and A. oryzae in koji making on enzymatic systems, physicochemical indexes and the volatile compounds of koji was investigated. Results showed that when the yeast inoculation was approximately 1.5×106 yeast per gram of koji and A. oryzae inoculation quantity was 0.15%(w/w), the neutral protease activity was 3100 U/g at 36 h. whereas the α-amylase activity in the yeast-inoculated sample decreased by 22%, the saccharifying enzyme activity increased by 7%, and no significant difference in peptidase activity between the yeast-inoculated sample and the control group. At the end of the koji making the concentrations of aim nitrogen and reducing sugar were almost the same between the yeast-inoculated sample and the control group, and Organic acid content was lower than the control. 32 and 23 volatile components were identified by GC-MS in the yeast-inoculated sample and the control group, respectively. By comprehensive analysis, inoculated a halophilic aromatic yeast in koji-making had not inhibited the growth of A. oryzae, but improved the flavor and quality of the finished koji.3. In this study we inoculated koji with a halophilic aromatic yeast(Z. rouxii) and A. oryzae and investigated the effects on the volatile compounds and quality of soy sauce moromi. Our results suggest that there were no significant changes in the concentrations of amino nitrogen, total titratable acids, total soluble nitrogen and reducing sugar by extending the fermentation time during the first fermentation month, whereas the concentration of glutamate in the yeast-inoculated sample increased by 46.16% and the arginine concentration decreased by 61.07%, in comparison with the control group. After the second fermentation month 17, 38 and 38 volatile components were identified by GC-MS in C1(0), C2(1.5×106 yeast per gram of koji) and C5, respectively. Moreover, a large number of volatile components, such as 2-Methoxy-4-vinylphenol,ethyl acetate and 3-Methylthio-1-propanol were found in C2 and C5. And the total contents of volatile compounds in C2 were obvious higher than C5.