Strain Improvement And Process Research On Soy Sauce Production

Soy sauce is a traditional fermented food. Strain is the basis of fermentation. Strains mutagenesis and selection is one of the core technologies of modern fermentation industries. As the core and basis of soy sauce production,Aspergillus oryzae directly affects the quantity of the output and quality of soy sauce. UV mutagenesis is not only the most commonly used method in mutation breeding, but also the most effective as its high mutation frequency and not easy of reverse mutation. It has been one of the favorite methods of many micro-organisms workers. However, due to gene mutation with variable tropism, it is difficult to obtain a good strain with comprehensive enzyme system by mutation. Thus mutation has a heavy workload and a lot of uncertainties. Therefore, how to carry out microbial genetic breeding quickly and efficiently has been the focus of genetic breeding.In today's soy sauce industry, the commonly used technologies are the high-salt liquid-state fermentation which is used mostly in Japan and the low-salt solid-state fermentation process represented by our China's state enterprises .However, no matter what kind of technology to be used, there are unavoidable problems. The salt inhibition of enzyme activity and the contamination control in fermentation conditions. Without the contamination of uncorrelated bacteria, liquid fermentation can be carried out in pure culture and maximize the activity of enzymes, so it has great application prospects.Based on the issues above, the following four main researches have been done in this paper.1. UV mutagenesis and breeding. Aspergillus oryzae 1-7.3 as the original strain was mutagenized by UV rays and screened with PDA medium containing different concentrations of the Nystatin as selecting pressure. We achieved primary screened 125 mutants which grow faster and change in the color of spore and colonial morphology. A modified objective mutant 80110 in multienzyme system was obtained by the secondary screening of koji-making, whose activities of acidic protease and neutral protease increased by 230.10 % and 17.50 % than original strain, respectively. Its glucoamylase dynamic decreased than 1-7.3, but which still increased by 15.10 % than 3.042.Whether the strain obtained could be used for the industrial production, we evaluated it through the comparison of three strains 80110, 1-7.3 and 3.042 in the level of soy sauce fermentation. The result showed that no mater in terms of total nitrogen, amino nitrogen or amino nitrogen generation rate, soy sauce produced by 80110 was better than 1-7.3 and 3.042, no other abnormal physical and chemical indicators.2. Protoplast fusion breeding. Two mutants 30023 and 3001 obtained in UV mutation breeding which have different advantages in enzymes and with different spore color were used as the parents for protoplast fusion. By using spore color difference and protoplasts inactivation technique, we have screened an excellent fusion strain R10 fast and efficiently.R10 can produce neutral protease and acidic protease in higher level than the parent strains and 3.042. Its acid protease activity increases particularly large. Although its glucoamylase dynamic is not as good as parents, but sill significantly higher than 3.042. Low-salt solid-state fermentation contrast between R10 and 3.042 ,the results showed that under the same condition, after 15 days the soy sauce was fermented by R10, whose total nitrogen content is lower than 3.042 ,the content of amino nitrogen is all square with 3.042 , the productivity of amino nitrogen and total acid content are both higher than 3.042; after 20 days, the soy sauce was fermented by R10, whose total nitrogen content, the content of amino nitrogen, the productivity of amino nitrogen and total acid content are all significantly higher than 3.042.3. The exploration of the new pure culture and liquid-state fermentation technology. In order to develop a high-quality, high raw material utilization and low-cost soy sauce fermentation process, the solid-state fermentation was combined with the liquid-state fermentation based on the traditional soy sauce production process. The best shake-flask culture conditions were identified as the medium milk: bran extract = 1:1, temperature 30℃, shaking speed of 160 rpm, the volume of liquid 12 %, incubation time 84 h. Under this condition, two forms of non-salt soy sauce liquid fermentation experiment were performed.