Identification,Characterization,and Probiotic Potential Of Lactobacillus Casei Isolated From Infant Feces

As a probiotic,Lactobacillus casei has attracted more and more attention due to its nutritional value and health care function,and related research has increased year by year.The aim of this project was to screen Lactobacillus casei from infant feces and to test the growth characteristics of Lactobacillus casei,tolerance to the Simulated gastrointestinal environment,adhesion,bacteriostatic,antioxidant and antibiotic resistance to provide theoretical support for its application in food and health care products industries.The main findings are as follows:?1?Screening and identification of Lactobacillus casei.Seventy-three strains of lactic acid bacteria were screened from fresh feces of healthy breast-fed infants,among which thirteen strains were Lactobacillus casei.All selected lactic acid bacteria were stored in the lactic acid bacteria resource bank of the State Key Laboratory of Food Science and Technology of Nanchang University.Three strains of Lactobacillus casei,which were well tolerant to acid and bile salts,were selected,numbered NCU011056,NCU011057 and NCU011061,respectively.?2?Growth and metabolism curve and antibiotic resistance of three strains of Lactobacillus casei.The growth trend of three strains of Lactobacillus casei all were S-type growth.And the main product of fermented glucose was lactic acid,which did not produce acetic acid.NCU011056 has the shortest lag phase and the highest lactic acid accumulation in the three strains,and the final pH was relatively lowest at about3.58.Three strains of Lactobacillus casei were all sensitive to penicillin,amoxicillin,ceftriaxone,tetracycline,chloramphenicol,erythromycin,rifampicin,and ciprofloxacin.?3?Tolerance and adhesion properties of three strains of Lactobacillus casei to simulated gastrointestinal environment.Three strains of Lactobacillus casei,especially NCU011056,were highly tolerant to high salt,acid and bile salts.The survival rates of NCU011056 were 95.7%,87.2%and 80%after treatment for 10%sodium chloride,pH 2.0 and 0.3%bile salts,respectively.The Co-aggregation rates of three strains of Lactobacillus casei were all above 70%after 24 h,among which NCU011056 had the highest Co-aggregation rate of 83.81%.The hydrophobicity rates to p-xylene of three strains of Lactobacillus casei were all above 86%.The adhesion rate to Caco-2 cell line of three strains of Lactobacillus casei was 14.52-60.28%,and the adhesion rate of NCU011056 was 60.28%.?4?Antibacterial activity and antioxidant activity of the three strains of Lactobacillus casei.The fermentation supernatants of three strains of Lactobacillus casei showed antibacterial activity against four common Gram-positive and Gram-negative indicator bacteria,and the bacteria were not bacteriostatic.There were other antibacterial substances besides lactic acid in fermentation supernatants of three strains of Lactobacillus casei,which was insensitive to protease and hot.The cell of bacterial and intracellular extracts of three strains of Lactobacillus casei all showed DPPH free radical scavenging ability,ability to reduce Fe³⁺and anti-lipid peroxidation ability.The anti-oxidation ability of the intracellular extracts of three strains was generally higher than that of cell of bacteria,among which the intracellular extract of NCU011056 had the highest antioxidant capacity.