The Causes Of Fermented Soybean Paste Quality And Optimization Of Fermentation Conditions

Soy sauce production origins in China, it is a traditional condiment of our people, because of its unique flavor, rich in amino acid content, loved by the majority of the people. In recent years, rerearches about starter-making, post-fermentation and flavor substances are hot issues. The experiment compared the protein activity and protein composition by means of trichloroacetic acid precipitation and SDS-PAGE electrophoresis. Then it analysis the amino nitrogen content, free amino acid content and flavor substances by means of potentiometric titration, amino acid analyzer and solid-phase microextraction coupled with GC-MS(Gas Chromatography-Mass Spectrometer). To optimize the fermentation conditions with index of amino acid nitrogen content for inspection of soy sauce fermented by choosing the best fungus by the response surface method. The details follows:1. The protein activity, protein composition and amino acid by different fungusUnder the same temperatures Aspergillus oryzae As3.042 protease activity was higher than the other three (Aspergillus niger; Rhizopus; Mucor Mucedo). Neutral protease activity of Aspergillus oryzae As3.042; Rhizopus; Mucor Mucedo was higher. Aspergillus oryzae As3.042 protein bands was significantly more than the other three.All the figures illustrates that the aspergillus oryzae As3.042 contains richer protein. Four soy sauce amino nitrogen content is on the rise with growing, during the fermentation time aspergillus oryzae As3.042 starter-making sauce amino acid nitrogen content in the whole period is higher than other three kinds of sauce. So aspergillus oryzae As3.042 proteinase hydrolysis, therefore, is stronger than other three. At 65 d, Aspergillus oryzae As3.042 soy sauce has the most abundant flavor components and the highest free amino acid content174.17 mg/g dry weight the other three (Aspergillus niger; Rhizopus; Mucor Mucedo) is 68.27、74.8、63.05 mg/g dry weight. It has the has 32 kinds of amino acids species and 7 kinds of essential amino acid content is 72.38 mg/g, the other three (Aspergillus niger; Rhizopus; Mucor Mucedo) is 27.30、32.28、27.21 mg/g dry weight.All of the results show that the optimal strain is Aspergillus oryzae As3.042 by these indicators.2. Flavor compounds of four kind soy sauce of different post-ferment timeThe characteristic volatile flavor compounds of soysauce after 40d was 2.3-butanediol, benzaldehyde, phenylacetaldehyde,3-methyl butanal, acetic acid,2-methyl butyric acid,4-methyl-pentylacid,3-hydroxy-2-butanone,guaiacol,maltol,2,3,5-trimethyl pyrazine as the component; at the fermentation of 60d, the characteristic volatile flavor components of soy sauce was 2,3 butanediol, 1-octen-3-ol, n-pentanol, phenylacetaldehyde,3-methyl butanal,2-methyl butanal, iso-valeric acid,3-octanone. With prolonged fermentation, the main types of volatile flavor compounds decreased, esters spices become more abundant; and alcohols and acids were the largest proportion of the material. Soy sauce fermented by Aspergillus oryzae As3.042 had more volatile flavor compounds than the other three. There are significant differences between them, specifically the most abundant species of the esters.3. Optimization of fermentation conditions for improving ferment conditions of soy sauce fermented by Aspergillus oryzae As3.042 using response surfaceTo optimize the fermentation conditions with index of amino acid nitrogen content for inspection of soy sauce fermented by aspergillus oryzae As3.042 by the response surface method. Firstly, theexperiment was to determine the optimum fermentation conditions at 40d of temperature, density of adding salty water and adition of salty water by using single factor experiment. On the basis of single factor experiment with amino acids as examining index, fermentation temperature, density of adding salty water and adition of salty water was optimized by using response surface analysis. We get the regression model which is the optimum process for the temperature of 40.28℃, density of adding salty water of 9.66%(the percentage of quality) and addition of salty water of 74.70%(the percentage of volume) Under the condition of fermentation, the content of amino acid nitrogen was 0.8376g/kg, close to the theoretical value (0.841g/kg), can provide the basis for practical production.