Characterization of lactic acid bacteria isolated from human breast milk and their bioactive metabolites with potential application as a probiotic food supplement

Abstract

The probiotic properties of twenty-five lactic acid bacteria (LAB) isolated from human breast milk were investigated through their resistance to gastrointestinal conditions and proteolytic activity. Seven LAB were identified and assessed for their auto- and co-aggregation capacity, antibiotics resistance, and behavior during in vitro gastrointestinal digestion. Three Lacticaseibacillus strains were further evaluated for their antifungal activity, metabolites production (HPLC-Q-TOF-MS/MS and GC-MS/MS) and proteolytic profile (SDS-PAGE and HPLC-DAD) in fermented milk, whey, and soy beverage. All strains resisted gastrointestinal conditions with viable counts higher than 7.9 Log10 CFU/mL after in vitro gastrointestinal digestion. Bacterial auto- and co-aggregation reached values up to 23 and 20%, respectively; with remarkable proteolytic activity for 18/25 strains. L. rhamnosus B5H2, L. rhamnosus B9H2 and L. paracasei B10L2 inhibited P. verrucosum, F. verticillioides and F. graminearum fungal growth, highlighting L. rhamnosus B5H2. Several metabolites were identified, including antifungal compounds such as phenylacetic acid and 3-phenyllactic acid, and volatile organic compounds produced in fermented milk, soy beverage, and whey. SDS-PAGE demonstrated bacterial hydrolysis of the main milk (caseins) and soy (glycines and beta-conglycines) proteins, with no apparent hydrolysis of whey proteins. However, HPLC-DAD revealed alpha-lactoglobulin reduction from 100% (control) up to 18% and 46% in milk and whey, respectively, with the highest proteolytic activity for L. rhamnosus B5H2. In overall, the three selected Lacticaseibacillus strains demonstrated probiotic capacity with L. rhamnosus B5H2 as remarkable potential for further study and application in generating bioactive metabolites and peptides able to promote human health.