| Soy milk, one kind of traditional Chinese food, is made from soybeans through soaking, milling, boiling and filtration processes. It is rich of nutrition and deeply loved by the majority of consumers, so its production is of great significance. Fresh soy milk has been sold in the market at present, but its shelf life is short. With the popularization of soy milk machine and the enhancement of people’s health consciousness, more and more people choose fresh nutritious and ready-to-make soy milk, what’s more, the taste of self-made soy milk can be adjusted freely. However, in traditional soy milk production process, soybeans are generally needed to be soaked for a dozen of hours. Making soy milk from dry soybeans is convenient and quick, but the soy milk is low in protein content and not easy to be absorbed, and the taste is inferior to that from soaked soybeans. Therefore, it is urgent to solve these problems to make the preparation process more convenient and the soy milk more nutritious. The soaking-free soybean which only takes consumers a few minutes to rehydrate before making soymilk can avoid these problems. The processing technology including fully soaking the selected soybean ingredients, partial dehydration drying and sterilization, and the shelf life were thus researched in this study. The main research results were listed as follows.After optimizing the conditions of differernt process stages, the best processing technology of soaking-free soybean products was achieved. In pre-treatment stage of raw material, soybean ingredients were soaked for 10 min in 10 mg/L ClO2 solution; in soaking stage, soybeans were soaked in a compound solution consisting of 0.5% NaHCO3 solution, 1‰ sodium D-isoascorbate and 0.3%o natamycin for 12 h at 15℃; in dehydration stage, the moisture content of soaked soybeans was dried to (20.0±1.0)% by hot-air at 60℃; in insterilization stage, the dried soybeans were microwaved for 30 s at a power of 4.67 W/g, and then irradiated with 10 kGy after vacuum packaging.To investigate the quality of soy milk made from soaking-free soybeans, the effects of five different pre-treatments of soybean, i.e. soaking-free soybeans, un-processed raw soybeans, soybeans soaked by traditional method, soybeans soaked by NaHCO3 solution, soybeans cooked by high temperature and high pressure, on soy milk’s quality, the sensory quality, color, stability, main nutritional ingredients and anti-nutritional factors’s content of soy milk were contrasted and analyzed. The results indicated that different pre-treatments of soybean had different effects on soy milk’s quality. Compared comprehensively, the sensory quality, color, stability and nutritional value of soy milk made from soaking-free soybeans significantly outperformed that from un-processed raw soybeans, soybeans soaked by traditional method, soybeans cooked by high temperature and high pressure. The protein content of soy milk made from soaking-free soybeans was 43.9%,15.9%,62.0% higher than that from un-processed raw soybeans, soybeans soaked by traditional method, soybeans cooked by high temperature and high pressure, respectively, and the polysaccharide content was 63.0%,34.5% higher than that from un-processed raw soybeans, soybeans soaked by traditional method, respectively. The quality of soy milk made from soaking-free soybeans was not so good as those from soybeans soaked by NaHCO3 solution, with inferior sensory quality, poorer color and stability, but the differences were little, and the contents of main nutritional components were higher than those from the latter, while the content of anti-nutritional factors was close each other, and it was more convenient to make soy milk from soaking-free soybeans. Therefore, making soy milk from soaking-free soybeans is not only convenient and quick, but also healthy and nutritious.The parameters which had significant effect on the quality of soaking-free soybean, such as microbiological indicator (total bacterial count), sensory index (browning index of soybean, sensory score of soy milk), physical and chemical indexes (protein and soluble solids content of soy milk) were chosed to judge whether soaking-free soybean products were spoiled or not. With the color, stability of soy milk and the rehydration ratio of soaking-free soybean considered, the change rules of those indexs along with storage time at 25℃ and 4℃ were studied. The results showed that, with the extension of storage time at 25℃ and 4℃, the rehydration ratio of soaking-free soybean decreased gradually; browning index and total bacterial count increased significantly (P＜0.05); the color of soy milk made from soaking-free soybean darkened gradually, total color difference showed a trend of increase overall; the protein and soluble solids content, stability and sensory score of soy milk all showed a declined trend; the protein and soluble solids content in the 90th day reduced 19.7% and 21.0% than the 0th day at 25℃; while the protein and soluble solids content in the 210th day reduced 20.4% and 16.1% than the 0th day at 4℃. Consided all the selected indexes the shelf lives of soaking-free soybean products were judged to be 80 day at 25℃ and 180 days at 4℃. |
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