Study On The Improvement Of The Enzyme Activity Of Aspergillus Oryzae Koji And The Promotion Of Fermentation Process

Soy Sauce is one kind of common condiment which is rich of nutritional value. Soy sauce is based on protein materials and starch materials for the main raw material and it is brewed by microorganism fermentation. Koji-making is the key in soy sauce-making. The purpose of koji-making is to make Aspergillus oryzae full growth, then the maximum enzyme activity and the best composition system on enzymes. The growth sitution of Aspergillus oryzae in the koji is related to the protease and gluco-amylase activity, and ultimately related to the quantity and quality of soy sauce.Low-salt solid-state fermentation have these characteristics:short fermentation period, high total nitrogen utilization, not very well played yeast, and lack of flavor. While high-salt liquid-state fermented soy sauce taste delicious with fruity esters, but fermentation period is long because of low fermentation temperature. Two processes have their own advantages and disadvantages. The combination of the two fermentation processes was made in order to discuss the relationship between temperature, salt content and the quality of soy sauce.Based on the issues above, the following three main researches have been done in this paper.1. The effects of additives on the enzyme activity of Aspergillus oryzae koji. Based on the single factor experiments of additional carbon source, nitrogen source and inorganic salt, the orthogonal experiment was investigated. The optimum condition were glucose 0.25%, NaNO3 0.1%, ZnSO4 0.05%. The result of verifying test indicated that neutral protease activity reached 2383.83U/g dry matter and gluco-amylase 117.82U/g dry matter in soy sauce koji, which were increased by 36.75% and 46.02% respectively compared with the control. Furthermore, several indices such as the total nitrogen and amino nitrogen by the optimal condition were higher than those by the blank in low-salt solid-state fermentation of soy sauce.2. Exploration of new soy sauce production process, which was to explore the temperature, salt content on the impact of soy sauce. The variation of several enzymes activity, amino nitrogen content, total sugar content, reducing sugar content were tracked in the experiment. Results indicated that temperature has a great influence on the enzyme activity. Low temperature was conducive to the preservation of enzymes activity, whereas fermentation temperature of the blank group was 45℃which was bad for the preservation of enzyme activity. But the low temperature will reduce the rate of enzymatic reaction, the physical and chemical indicators of the experimental group(including soy products and the indicators during the fermentation) was lower than the control. Among them, the increase of amino nitrogen content was limited in the low-temperature stage, while increased significantly in the latter stage compared to the low-temperature phase. For the soy products, although the total nitrogen content of the experimental group was lower than the blank group, but the amino nitrogen formation rate of the experimental group was higher than the control, which indicated that previous low-temperature fermentation was benefit for total nitrogen converted to amino nitrogen. In the experiment of exploring of two-stage fermentation process, free amino acids content of the three experimental groups was lower than that of the blank group. But the content of delicious amino acids in the experimental group of 15% salt was increased 21.42% compared with the control. The content of bitter taste amino acids was decreased 20.12% compared with the control. It showed that low-temperature fermentation was conducive to increase the delicious amino acids and decrease the bitter taste amino acids. On the experiment of improving two-stage fermentation process, the new process might be determined as: pre-fermentation at 45℃for 15 days, post-fermentation at 30℃for 10 days, the fermentation period was 25 days.3. Wheat in the original formula was replaced by wheat starch for soy sauce fermentation in accordance with soybean meal:bran:wheat starch=10:4:1, which improved the quality and flavor of soy sauce and also took full advantage of wheat starch byproduct and reduced the costs of soy sauce production.