Screening Of Lactic Acid Bacteria From Breast Milk And Baby Infant And The Effect Of Fermented Milk Quality

Probiotics can provide multiple health benefits for the host,and screening of lactic acid bacteria strains with probiotic functions has become a research hotspot in food science Breast milk is the most nutritionally balanced food during the growth of babies,and the probiotics screened from breast milk have better safety and probiotic properties.In this paper,lactic acid bacteria strains were isolated from breast milk of healthy women and feces of healthy infants in Hunan province,China.Probiotics with potential probiotic functions were screened by studying the tolerance of the strain to the simulated artificial gastric and intestinal fluid environment,the ability to inhibit bacteria,the ability to adhere to Caco-2 intestinal epithelial cells,the oxygen tolerance of Bifidobacterium,the antibiotic sensitivity to produce amines and hemolysis,etc;And mixed fermentation with Streptococcus thermophilus grx02,the fermentation characteristics of its fermented milk were determined,in order to obtain the independent intellectual property rights of maternal and infant probiotic strains with potential probiotic characteristics and good fermentation characteristics,applied in fermented food or probiotic preparations.The main research contents and results of the experiment are as follows.(1)Screening and identification of lactic acid bacteria from breast milk and infant feces.10 samples of breast milk from healthy women of different ages and different lactation periods and 2 samples of healthy infant feces of different genders and different ages were collected in Hunan province,China.Lactobacillus,Lactococcus and Bifidobacterium were isolated by MRS medium,M17 medium and modified MRS medium(mopirocin lithium salt,cysteine hydrochloride solution).97 strains of lactobacillus were isolated from breast milk samples,and 32 strains were isolated from infant feces samples through acid production test A total of 46 strains of Lactobacillus were screened out,including Lactobacillus rhamnosus,Lactobacillus paracasei,Lactobacillus casei,Lactobacillus fermentum and Lactobacillus plantarum,10 strains of Bifidobacterium were screened out,including Bifidobacterium longum,Bifidobacterium breve and Bifidobacterium bifidum,Enterococcus faecalis 83 strains.(2)Study on in vitro functional characteristics of probiotics from breast milk and infant feces.The isolated lactic acid bacteria with acid-producing ability were all able to tolerate in the artificial gastric juice with pH 2.5.Only 4 strains of Lactobacillus and 4 strains of Bifidobacterium had a survival rate greater than 1%in the 0.1%bile salt,and the survival rate of B.breve was higher,while the survival rate of the other strains were all less than 1%.4 strains of Lactobacillus and 3 strains of Bifidobacterium to Caco-2 intestinal epithelial cells are quite different of the adhesion abilities,and the number of L.plantarum cells is the largest,up to 57.4 strains of Lactobacillus were able to inhibit 3 strains of Gram-positive bacteria and 2 strains of Gram-negative bacteria,3 strains of Bifidobacteria have no inhibitory effect on Staphylococcus aureus and Bacillus cereus.4 strains of Lactobacillus are sensitive to cephalosporins,rifampicin and chloramphenicol,4 strains of Bifidobacteria are sensitive to vancomycin,penicillin G and chloramphenicol.Lactobacillus and Bifidobacteria in the histidine and tyrosine decarboxylase medium,the color is yellow and the state is turbid,indicating that the strain did not produce amines during the growth process.There was no hemolysis in the Columbia blood AGAR plate,which indicated that the screened Lactobacillus and Bifidobacterium were safe and could be used in the development of fermented milk.(3)Study on the effect of lactic acid bacteria from breast milk and infant feces on the quality of fermented milk.4 strains of Lactobacillus with potential probiotics and Streptococcus thermophilus grx02 were mixed and fermented separately.After 6 h of fermentation,the viable bacteria number of Lactobacillus single fermentation milk and the mixed fermentation milk with S.thermophilus grx02 reached more than 108 CFU/mL.Above,the number of viable bacteria in the same single fermentation is less than the number of viable bacteria in mixed fermentation.Before 4 h of fermentation,the pH and titrated acidity of the 4 strains of Lactobacillus and S.thermophilus grx02 mixed fermented milk showed an accelerated decreasing trend and an accelerated increasing trend,respectively.The pH was between 3.60 and 3.80,and the titrated acidity was between 90°T and 95°T.The viscosity of mixed fermented milk with different Lactobacillus and S.thermophilus grx02 showed a decreasing trend during storage,in which the viscosity of mixed fermented milk with L.plantarum M113 and S.thermophilus grx02 was 1420 cP after 15 days of storage,showing good taste.The hydraulic capacity of mixed fermented milk with different Lactobacillus and S.termophiilus grx02 showed a decreasing trend during storage.The hydraulic capacity of mixed fermented milk with L.plantarum M113 and S.thermophilus grx02 was maintained at 53.40%after 15 days of storage,showing good tissue stability.The gel strength of mixed fermented milk with different Lactobacillus and S.thermophilus grx02 showed an increasing trend during storage.The gel strength of mixed fermented milk with L.plantarum M113 and S.thermophilus grx02 increased to 0.201 N after 15 days of storage,showing strong anti-deformation ability and solid grid structure.