The High-density Cultivation Of Lactobacillus Bulgaricus And The Development Of Soybean Fermented Beverage

This thesis is mainly about the high-density cultivation of Lactobacillus bulgaricus and the development of soybean fermented beverage. Including the optimization of Lactobacillus bulgaricus medium and culture conditions, the inhibition methods of soybean lipoxygenase activity, the inhibition methods of soybean trypsin inhibitor activity, the optimization of soybean protein hydrolysis conditions and the nutritional analysis and sensory evaluation of soybean fermented beverage. The aim of this study was to develop a kind of high-quality soybean fermented beverage with the prospect of high nutritional value and good sensory taste.The influence of carbon and nitrogen sources, multiplication factors, and inorganic salts on high-density culture of Lactobacillus bulgaricus were discussed by using the method of response surface design to optimize the bacteria fermentation medium. The impact of temperature, initial pH and inoculum size on high-density culture were studied in order to determine the optimum culture conditions. The optimum culture conditions were that temperature 42℃, initial pH7.5 and inoculation 3%. The maximum cell density (OD value) increased by 30.16%, from the original 1.104 to 1.437. Cell concentration reaches 1.2X 109cfu/mL. Comparing with pre- optimization (1.4×108cfu/mL), it increased 8.57 times. In 5L fermentor, the cell of L. bulgaricus grew very fast, and it could achieve the highest cell concentration in 6 hours. The maximum biomass concentration was 1.701(OD value), which is to say that a large-scale industrial production was possible.By comparing the soybean lipoxygenase activity of different treatment, the best method was chosen and the parameters of the conditions were optimized to eliminate the activity of soybean lipoxygenase. In several pre-processing methods, heat grinding method was the most effective one. Among various factors of heat grinding method, the most important one was scalding temperature,then refining temperature and the last one was scalding time. The best process parameters were that the scalding temperature 95℃,the scalding time 5min and the refining temperature 100℃. Under these conditions, checking the activity of soybean lipoxygenase, the result was only 360U/g, which was 7.89% of pre-treatment.By studying different treatment with the soybean trypsin inhibitor activity, the best method was chosen and the parameters of the conditions was optimized to eliminate the activity of soybean trypsin inhibitor. Heat grinding method was most effective. Among various factors of heat grinding method, the most important one was scalding temperature, then refining temperature and the last one was scalding time. The best process parameters were that the scalding temperature 95℃, the scalding time 5min and the refining temperature 100℃. Under these conditions, checking the activity of soybean trypsin inhibitor, the TIU was only 7.5, and that was 28.41% of pre-treatment.Using protease to hydrolyze soy protein into lower peptide, was found conducive to the growth of Lactobacillus bulgaricus, and also conducive to the health of human body. The optimized process of soybean enzyme hydrolysis significantly promoted the fermentation process of soybean milk, not only improved the titration acidity of the fermentation process but also accelerated the rate of acid production. And it shortened the fermentation time, while improving the quality of soybeans fermented beverage. As a result of that, it can reduce the risk of bacterial contamination, and reduce costs.The acidity and pH value of the fermented soybean beverage were assessed. By studying several key factors on the impact of product quality, the production process was optimized and the product quality was improved. The nutrition value of soybean fermented beverage was determined, and the sensory was assessed, comparing with the yogurt. From the view of process conditions, temperature was the most significent factor, then was the amount of glucose and third one was pH value. The inoculum and bacteria ratio was following. The optimum conditions were glucose 5%,the initial pH value 7.5, fermentation temperature 42℃, inoculation volume 4% and bacteria ratio 1:1. The response surface analysis showed that, when the temperature was 42.13℃, glucose concentration was 4.97% and the pH value was 7.42, the titratable acidity of the fermented soybean beverage came to the result of 69.84°T.The soybean fermented beverage developed by this thesis was not only eliminated the beany flavor and inhibited the trypsin activity, but also comparable with yogurt in nutrient composition and sensory flavor, and had a very broad prospect for development and utilization.