Screening And Identification Of Lactobacillus Acidophilus And Study On Its Preparation Of Bacterial Agent

Fermented soymilk is a pruduct fermented by lactic acid bacteria which has special flavor.It is rich in protein and easy to digest and absorb,which is helpful to regulate gastrointestinal function and overcome lactose intolerance.In order to develop a lactic acid bacteria fermented compound soymilk with rich nutritive value and no beany flavor.In this study probiotic lactic acid bacteria suitable for soymilk fermentation were screened and its growth characteristics,probiotics function and fermentation technology were studied.The main conclusions are as follows:(1)Screening and identification of lactic acid bacteria.Two strains with tolerance to low p H were screened and identified as Lactobacillus plantarum by morphological,physiological,biochemical characteristics and molecular biological identification.The optimal strain were selected by the comparative test of soy milk fermentation,and named NCU1124.(2)Growth characteristics of NCU1124.The results of the growth curve determination indicate that the delay period is 0 to 2 h,2-10 h is the logarithmic phase,10-28 h is the stability period,and it began to enter into decline phase after 28 h.NCU1124 has strong gastrointestinal tolerance.After 3 h in MRS medium with p H 2.0,the viable cell number of the strain reaches 6.98 lg(CFU/m L);the survival rate in MRS with 0.3 g/L bile salt for 4 h was 80.9%;and after 12 h in artificial gastrointestinal fluid,the viable cell number still remain 10~9 cfu/m L;Morever,the strain maintained for more than 10~9 cfu/m L under hyperosmotic condition after 24 hours.(3)Antibacterial properties.NCU1124 has a strong inhibitory effect on eight common pathogens.It was showed the inhibition to Pseudomonas aeruginosa was the strongest with the diameter of the inhibition area being more than 23 mm;NCU1124cells didn't have bacteriostasis.There were other antibacterial substances except for lactic acid.The bacteriostasis of the fermentation broth was not affected by the treatment of high temperature,peroxidase and protease.(4)Fermentation technology of compound soymilk.The fermentation conditions were optimized by single factor experiment and orthogonal experiment with sensory evaluation and viable cell number as index.The results showed that the optimized condition was:culture for 30 h at 30°C with inoculum concentration of 0.02%and syrup of 8%.The optimum sugar degree was 2%to fermented compound soymilk.(5)Quality analysis of fermented compound soymilk.By comparing the changes of compound soymilk components before and after fermentation,the content of small peptide,total amino acid and soybean isoflavone were found to be significantly improved;the content of fat and soluble solids was lower than before fermentation,and the content of protein was not changed after fermentation.The aroma components species and contents of compound soymilk increased significantly,which greatly enriched the flavor of compound soymilk.In addition,ABTS and FRAP antioxidant capacity increased significantly after fermentation.(6)The storage stability of fermented compound soymilk at 4°C and room temperature(25°C)was measured by different indexes.It was found that the high temperature had a great influence on viable cell number,viscosity,water retention and sensory.As a result,the products were suitable for storage at 4°C.