Study On Extruding Soybean Meal And Flour At Low Temperature For Making Soy Sauce

Compared with the traditional cooking method, low temperature extrusion technology that used in soy sauce fermentation can achieve the purposes of improving protein and amino acid utilization, shortening the fermentation period and reducing energy cost. Technology parameters of extrusion process, koji-preparing process and fermentation process were optimized in this study with volatile compound analysis and amino acid content were also detected with solid phase microextraction and automatic amino acid analyzer. We get the following conclusion through test:(1) The optimum extrusion parame ters of the mixture of soybean meal and flour at low temperature was determined. Make the soybean meal as the main raw material and flour as the auxiliary material. Four test factors, including temperature of barrel, moisture of material, proportion of flo ur and speed of screw, were employed to design test with protein digestibility, water soluble protein content, gelatinization degree, swelling degree and moisture content as indicators. The optimum parameters of extrusion were obtained by response surface methodology of SAS 9.1.3: the temperature of the barrel is 90 ℃, the proportion of flour is 20%, the moisture of material is 20%, the speed of the screw is 220r/min. Under this condition, the protein digestibility is 91.05%, the water soluble protein content is 24.13%, the gelatinization degree is 95.28% and the swelling degree is 222.64%.(2) The koji- making parameters, temperature of koji, proportion of bran, moisture of koji, and time of koji- making was determined in prepare the soy sauce koji with extruded raw materials. Make neutral protease activity as main indicator, and alkaline protease activity, saccharifying enzyme activity and the number of spores as assist indicators at the same time. The optimum parameters of koji-preparing process that op timized by response surface methodology of SAS 9.1.3 was shown as follows: the temperature of koji is 33℃, the proportion of bran is 25%, the moisture of koji is 90%, the time of koji is 42 h. With this condition, the neutral protease activity is 1792u/g, the alkaline protease activity is 1476u/g, the saccharifying enzyme activity is 541u/g and the number of spores is 54.1billion/g.(3) The optimum fermentation parameters, include the percentage of salt, the temperature of fermentation and the time of fermentation to make test were determined with protein utilization, amino acid nitrogen content, nitrogen content, no salt soluble solids content and total acid content as indicators. The optimum parameters of fermentation process were optimized by response surface methodology of SAS 9.1.3 and shown as follows: salt percentage is 11%, the temperature of fermentation is 46℃, the time of fermentation is 14 d. Under this condition, the protein utilization is 90.02%, the amino acid nitrogen content is 0.749g/100 m L, nitrogen content is 1.36g/100 m L, the no salt soluble solids content is 14.15g/100 m L, the total acid content is 1.208g/m L.(4) The volatile compounds in soy sauce were analysized. Determining the volatile compounds with combination of HS-SPME and GC-MS, 38 volatile compounds were indentified in soy sauce made from extruded the mixture of soybean meal and flour(EMSF), the main compounds were calculated with 7 alcohols, 4 phenols, 4 acids, 5 aldehydes, 1 amine, 1 ketone, 7 pyrazines and 9 esters, the relative content are 2.9%, 4.32%, 1.99%, 7.49%, 2.58%, 3.09%, 46.31% and 12.88%, respectively. 23 volatile compounds in soy sauce made form boiled mixture of soy meal and flour(BMSF),the main compounds were calculated with 4 alcohols, 2 phenols, 3 acids, 2 aldehydes, 1 amine, 4 pyrazines and 7 esters, the relative content are 3.16%, 0.67%, 1.79%, 1.70%, 18.97%, 35.12% and 22.37%, respectively. Methoxyphenols with the total relative content of 4.32% in sample made from EMSF were nearly 7 times more than the sample prepared by traditional method. Pyrazines and their derivatives occupied 1/3 of the total content of volatile compounds.(5) The free amino acid in soy sauce were analysized. Both samples had 17 kinds of amino acid, the total content and contents of 15 kinds of amino acids in soy sauce made from EMSF were significantly higher than that from BMSF. The total content of amino acids of EMSF is 4436mg/100 m L, and the total content of amino acids of BMSF is 3378mg/100 m L.