Evaluation of the potential probiotic properties of Lactobacillus strains isolated from traditional fermented yak milk

Probiotic strains require investigation to obtain functional products and to satisfy the increasing market demand for probiotics. Traditional fermented yak milk is a potential source of probiotic Lactobacillus strains. Lactobacillus isolates were identified on the basis of their physiological and biochemical characteristics and their probiotic properties were evaluated, including acidifying and coagulating abilities, tolerance to acid, bile salts and artificial gastrointestinal conditions, antimicrobial activity, antibiotic susceptibility, production of biogenic amines, hydrophobicity and adhesion to HT-29 cells. A total of 71 isolates of Lactobacillus were isolated from 15 samples of homemade fermented yak milk, which were collected from different individual households in the pasture region of Gansu, China. The isolates were identified as follows: Lactobacillus plantarum (23 strains), Lactobacillus acidophilus (21 strains), Lactobacillus casei (12 strains), Lactobacillus fermentum (7 strains), Lactobacillus brevis (3 strains), Lactobacillus minor (3 strains) and Lactobacillus curvatus (2 strains). Twenty-three isolates were preliminarily selected for further investigation based on their acidication capacity and coagulating properties. Of these, 14 isolates were fully tolerant to 0.3% bile salts and grew well when exposed to acidic conditions for three hours. The 14 isolates were further assayed by in vitro methods. None of the Lactobacillus isolates produced biogenic amines, and all showed varying tolerance to the simulated human gastrointestinal tract (GIT), possessed some antimicrobial activities and were susceptible to antibiotics. Seven isolates demonstrated more than 50% hydrophobicity. These seven isolates were then evaluated for their adhesion capability to the HT-29 epithelial cell line. Wide variations in the specic adhesion efficiency were observed. Two isolates, E2 and G12, were found to possess desirable probiotic properties in vitro. The two isolates were further identified by 16S rDNA gene sequencing analysis. Isolate E2 was identied as Lactobacillus acidophilus and G12 was most homologous to Lactobacillus casei.