Study On Multi-strain Koji-making And Enzyme Activity Regulation Of Aspergillus Type Douchi Koji

As China’s traditional soy-fermented products, Douchi was deeply loved by consumers because of its unique flavor and rich nutrition. However the production of douchi is mainly at natural fermentation. Long production cycle,uneven quality and health and safety hazards are still widespread in douchi enterprise. In order to further improve the product quality and the speed of the industrialized production, this paper has done some research. In this study,Aspergillus type douchi was the object of study, the optimal ratio of strain was obtained by complex koji-making with dominant strains which were screened from Yangjiang douchi koji, then the application of metabolic control technology in koji making process and optimization of multi-strain koji-making technology for Aspergillus type Douchi was studied,at last fermentation kinetics models was established. The main contents and results as following:(1) Koji was made by any two strains of the six which were screened from Yangjiang douchi koji. By comparing the neutral protease activity and the amino nitrogen content of the koji, Aspergillus oryzae A2 and B2 were screened as the optimal combination. Then Koji was made by Aspergillus oryzae A2 and B2 and Rhizopus oryzae R1 or R2. By comparing the neutral protease activity、β-glucosidase activity and the amino nitrogen content of the koji,Aspergillus oryzae A2 and B2 and Rhizopus oryzae R1 were screened as the optimal combination of complex koji-making.(2) Study the effect of different adding nitrogen sources on protease activity of koji.The results showed that the effect of organic nitrogen was better than inorganic nitrogen.And soybean meal had more significant effect. Compared with the control group, soybean meal can successfully increase protease activity by 10%. Therefore, soybean was chose forfollow-up study. Then using Aspergillus oryzae fermented soybean meal and made fermentation-promoting peptides. Adding it to the production process of koji-making, it was found that the growth of Aspergillus oryzae was significantly promoted. And comparing with koji without fermentation promoting peptides, the protease activity increased by 24.5%.(3) Research on optimization of multi-strain koji-making technology for Aspergillus type Douchi. The significant three effects, such as temperature, relative humidity and inoculation volume were determined through single factor test combined with Plackett-Burman design. The optimum technolgy was obtained by Central Composite Design; the results were fermentation temperature 30.5℃, relative humidity 81.5%,inoculation volume 5.12%, koji-making time 5d, addition of fermentation-promoting peptides 0.4%. Under the optimum conditions, protease activity was 527.09U/g andβ-glucosidase activity was 2.69U/g.(4) This paper discussed the dynamics of multi strain mixed fermented Aspergillus type douchi koji. The results showed that neutral protease activity and β-glucosidase activity were characterized as typical S-type curves and the kinetics models for them were established according to the Logistic model. The optimal parameters of models were obtained through mathematical derivation and nonlinear regression. The two kinetics equations were built,which characterized the douchi koji batch fermentation process very well. A good correlation between models calculated values and experimental data was observed, therefore, it will provide the theoretical basis for fermentation course control of Aspergillus type douchi koji.