Isolation and characterization of probiotics from fermented foods for developing synbiotic powder

Lactic acid bacteria (LAB) are a group of probiotics conferring health benefits. Several studies have reported that LAB can inhibit pathogenic bacteria in the digestive system, reduce blood cholesterol levels, and improve functions of the immune system. The objectives of this study were to isolate and characterize LAB from local fermented foods and to determine the probiotic properties for developing a synbiotic powder. Eighty three LAB isolates were first screened for the antibacterial activity against six pathogenic bacteria: Escherichia coli ATCC 25922, Salmonella typhimurium DMST 560, Pseudomonas aeruginosa DMST 4739, Staphylococcus aureus ATCC 25923, Bacillus cereus DMST 5040, and Salmonella enteritidis DMST 1567 by the cylinder plate method. Ten LAB isolates showing the highest inhibition zone against each pathogen were further selected for acid and bile salt tolerances. Three potential probiotic strains: P09, P10, and P11 exhibiting acid and bile salt tolerances were evaluated an antimicrobial activity of their culture supernatants after neutralization. Results showed that the neutralized supernatants did not show their antimicrobial activity, while non-neutralized supernatants did. Therefore, the antimicrobial activity of these strains may be due to organic acids presenting in the supernatants. All three isolates (P09, P10 and P11) also showed negative results for haemolytic and DNase tests. The 16S rDNA gene analysis revealed that P09, P10 and P11 isolates were all identified as Lactobacillus plantarum. The isolate L. plantarum P10 showed the highest adhesion to Caco-2 cells at the level of 4.52%. L. plantarum P10 was thus investigated the antibacterial activity against bacterial pathogens by a co-culture assay. The result demonstrated that the strain had a significantly inhibitory effect on the growth of E. coli ATCC 25922, S. typhimurium DMST 560, S. aureus ATCC 25923 and B. cereus DMST 5040 after co-incubating for 24 hours (p<0.05).
Additionally, L. plantarum P10 served as the probiotic starter for developing its synbiotic powder. The freeze-dried synbiotic powder was prepared by combining the strain with an inulin extracted from Jerusalem Artichoke together with skim milk or maltodextrin as a cryoprotectant. The developed synbiotic powder exhibited a high survivability of L. plantarum P10 under the simulated gastrointestinal (GI) conditions. However, the synbiotic powder formulated with skim milk showed a higher GI tolerance than that of maltodextrin. Moreover, the synbiotic powder with skim milk showed a relatively high stability in both its cell viability (more than 107 CFU/ml) and antimicrobial activity during storage at refrigerated and room temperatures. However, the antibacterial activity against 4 pathogenic bacteria (E. coli ATCC 25922, S. typhimurium DMST 560, B. cereus DMST 5040 and S. aureus ATCC 25923) still remained up to 12 weeks while keeping it refrigerated but only up to 8 weeks at room temperature. In conclusion, the results obtained from this study indicated that L. plantarum P10 satisfied the criteria for a potential probiotic and may be suitable for applying the synbiotic product against food-borne pathogens.