The Study On The Optimization And Mechanism During High-salt Soy Sauce Fermentation With Liquid State

Soy sauce is a type of traditional condiments which is very liked by people with very long history. The quality and per capital consumption of soy sauce are anything but satisfactory although the soy sauce production in our country is very large. In the article, Cantonese soy sauce produced by liquid fermentation with high salt, is the objective of our study.After separation, purification, morphology and microbial populations and individual microbial, the Aspergillus oryzae strains were got. After screening with casein plate medium, comparison of spore numbers and protease activity and generation stability test, the strain L-4 was used in the following study.The study on nutrient source of seed koji revealed that, glucose, soybean meal, ZnSO₄, CaCl2 had great influence. After the orthogonal design of the formula, the best formula was obtained, that was, glucose 1.00%, CaCl20.10%, ZnSO₄ 0.05%, soybean meal 3.00%, and the content of soybean meal was the significant factor. With the formula, the spore number was increased by 84.87%, to 15.77 billion/g dry seed koji. At the same time, the protease activity of seed koji and soy sauce koji were increased by 25.05% and 17.40%, respectively.As for soy sauce koji, the pretreatment of soybean and inducing effects on protease activity of soy sauce koji were investigated. The cooking temperature of 126℃and cooking time of 6 min were determined by comparison of steamed soybean digestibility. And the soybean meal was adopted among four different proteins, which were yeast extract, peanut meal, soybean meal and gluten. After the koji-making of soybean meal, enzymic hydrolysis, ultrafiltration and freeze drying, the fermentation-promoting peptides with molecular weight less than 3000 Da were collected. Using response surface methodology, the best process condition was 31℃, 45h, 0.45%, with the result koji in which neutral and acidic protease activity were 1890.12U/g dry koji and 776.55U/g dry koji. The rates of increase reached nearly 60% and 57%, respectively. It revealed that the fermentation-promoting peptides with molecular weight less than 3000Da, obtained by controlled enaymic hydrolysis of soybean meal koji, exerted metabolic regulation on Aspergillus oryzae and induction effects on the production of protease.At last, the artificial neural network was used to predict the brewing state of soy sauce and its changing pattern with regard to total nitrogen (TN) andα-amino acidic nitrogen (AN). After the 7-40-2 BP network with training precision of 10-4 and one hidden layer containing 40 neurons was determined statistically, the quite high R values of 0.9983 and 0.9953 between predicted and experimental data verified that the neural model was quite successful in predicting the experimental data points. Using the network, the effects of five input variables on two output variables were found in different way, and the R-values, which indicating the correlation between the TN and AN, ranged from 0.7298 to 0.9916. As for the relative significances of inputs, aging time is the key factor for both outputs during the moromi aging. As for other inputs, the order of importance was temperature > pH > neutral protease activity > acidic protease activity for TN, and temperature > acidic protease activity > neutral protease activity > pH for AN, respectively.