Study On Se-Enriched Lactobacillus And The Application In Soymilk Fermentation

The lactobacillus is commonly used for fermentation strains in food industry and has multiple biological functions, which has important health benefits to human health. The trace element selenium is an essential mineral nutrient and has bioactivities of anti-cancer, anti-oxidation, boosting the immune, improving reproductive performance involved in gene expression, protecting the body from reactive oxygen free radical damage, alleviating skin aging and other physiological activities. Soybean Milk can inhibit harmful intestinal bacteria growth, improve human immunity and reduce serum cholesterol levels and so on. Therefore, the use of the lactobacillus enriched inorganic selenium and selenium-enriched strains applied to the soy milk can achieve multiple health benefits, which has high practical value. In this study, we bred ability of selenium-enriched strains, and strains selenium-enriched fermentation medium and culture conditions were optimized. The Se-rich strains were applied to soy milk fermentation. The main results were as follows:The enriched ability of the selenium-enriched strains was screened from commercially available yogurt and identified. The results were consistent with Bergey bacterial identification manual identification. The results were Streptococcus thermophilus belong to abnormal branch Streptococcus gram-positive bacteria and named the Streptococcus thermophilus ZZ-1. The strains selenium enriched rate was reached43.43%by the strains of selenium-enriched test.The ultraviolet radiation and LiCl mutagenesis method were used. The results showed that the UV irradiation time of15s and lithium chloride concentration of1.0mg/mL were the best optimal mutagenic dose. The plant of high Selenium concentration Streptococcus thermophilus strain was obtained and named ZZ-CW4, which the selenium enriched rate was reached83.43%and increased by47.94%compared with the initial strain. Mutant strain ZZ-CW4after10generations of reproduction displayed its genetic traits and selenium enriched rate were stable.The effect of different nitrogen sources, inorganic salts and growth promoting factor on selenium-rich fermentation of Streptococcus thermophilus was studied, The optimal medium conditions of Streptococcus thermophilus selenium-enriched fermented from single factor and orthogonal experiments analysis were:glucose concentration of1%, the tryptone concentration of1%, tomato juice ratio of20%, dipotassium hydrogen phosphate concentration for2g/L, the MnSO4· H2O concentration content as3g/L. The enriched rate was more than85%determined by Streptococcus thermophilus modified medium formulation conditions through verification experiment.The effect of Streptococcus thermophilus fermentation temperature, initial pH, inoculum size, liquid volume, rotation speed, the initial concentration of selenium, selenium, bacteria of various age and incubation time strains on selenium enriched rate and biomass determined by single factor experiments. The most significant factors through the PB experiment determined by the impact of Streptococcus thermophilus selenium-enriched fermented were:the initial selenium concentration, plusing Selenium time and incubation time. The steepest climbing test was sufficiently close to the maximum response surface area by the steepest ascent test using response surface methodology to establish the mathematical model of the major impact factor of Streptococcus thermophilus enriched fermentation conditions. The optimal conditions of Streptococcus thermophilus enriched fermented impact factor conditions calculated were selenium time of20h, initial selenium concentration of19μg/mL and incubation time of36h. The predictive value and verification test were similar under optimal conditions. The Streptococcus thermophilus selenium-enriched was nearly90%after optimization.The selenium-enriched Streptococcus thermophilus were used for soymilk fermentation to determine selenium-enriched acid soy milk fermentation process. The concentration of3%Na2CO3solution soak was used for deodorization of soybean. The best soaking temperature and time were80℃and10h. When the soaked soybeans beating material to water ratio was of1:5, fermentation Soybean Milk quality is better. Adding a certain percentage in soymilk fermented milk can improve the flavor. The ratio of20%milk was mixed for the optimal amount by experimental study. Soybean Milk fermentation of various factors determined by orthogonal test size were:the inoculum size>fermentation time>sucrose add the amount>fermentation temperature. Under inoculum size of4%; fermentation temperature of42℃, fermentation time of5h and sucrose dosage of7%and the sensory quality score was the highest conditions. The best fermentation process conditions of enriched acid fermented soy milk were obtained.