Isolation And Optimization Of Bactericidal Methods Of Bacillus In Soy Milk

Bacillus is a microorganism that easily produces spores in adverse environments.The spore is extremely resistant to the adverse external environment,has the characteristics of thick cell walls and low water content.It is hard to be killed by heat,ultraviolet rays,radiation and various food preservatives.Bacillus is widespread in foods and is commonly found in infant and toddler dairy products,rice,and various soy products,posing a serious threat to food safety.In this study,Bacillus cereus and Bacillus subtilis were isolated from spoiled soybean milk.The?common?germination?agent?of?the?two?strains?was?studied,?and the germination promotion scheme was optimized.Bacillus which cannot fully germinate is treated to inhibit germination,and the best inhibition scheme is screened.The two-stage method combining germination promotion and germination inhibition methods is used to control the harm of Bacillus in food,to achieve the purpose of killing most Bacillus and controlling the germination of Bacillus.The main results are as follows:(1)Two strains were screened from spoiled soybean milk.Based on the colony morphology and 16 SrRNA identification,Z1 was Bacillus cereus and Z2 was Bacillus subtilis.(2)Determine the optimal germination pH of the spores.The optimum germination pH of the mixed bacteria of Bacillus is 6.5,and under this condition,the germination rate can reach 29.89%.(3)Determine the best germination strategy.The single-factor test and response surface test determined D-mannose concentration of 218 mmol/L,inosine concentration of 43 mmol/L,and rhamnose concentration of 97 mmol/L as germination-promoting combinations.At this time,the maximum germination rate was 86.10%.(4)Determine the best suppression plan.Single factor tests were used to screen out disodium ethylenediamine tetraacetate,?-polylysine and nisin for compounding test.The best inhibitor combination with the ratio of disodium ethylenediamine tetraacetate to ?-polylysine was 1: 3,and the maximum inhibition rate was 98.99%.(5)Z1 and Z2 were inoculated into sterilized soybean milk to verify the killing effect of the two-stage sterilization method on Bacillus in this study.The test results showed that the soybean milk after two-stage sterilization had no significant change in the colony number at 56 d at a storage temperature of 4 ?,and the sensory score was 93.9.