Purpose: This study evaluated the probiotic potential of indigenous lactic acid bacteria (LAB) isolated from raw milk and traditional Greek PDO Galotyri and Graviera cheeses.
Methods: Thirty representative strains of various taxonomic groups of LAB isolates were subjected to in vitro assays simulating the conditions prevailing in the human GI tract. All strains were screened for resistance to lysozyme, acid pH, bile salts, proteolytic enzymes (pepsin, pancreatin) and bile salt hydrolysis (BSH) activity.
Results: Responses were strongly strain- rather than species-specific, with only seven strains, Enterococcus faecium KE82, E. faecium GL31, Enterococcus durans KE100, E. durans GL70, Lactococcus lactis subsp. lactis KE109, Lc. lactis subsp. cremoris M104 and Lactobacillus plantarum H25, revealing a high probiotic potential. All strains were highly resistant to lysozyme, bile salts and pancreatin. Strains KE82 and H25 exhibited strong BSH activity towards taurodeoxycholate (TDC) and glycodeoxycholate (GDC), strains KE100, GL70 and GL31 hydrolyzed TDC strongly, whereas both lactococcal strains KE109 and M104 showed no BSH activity. Strains GL70 and M104 retained the highest viability (6 log CFU/ml) at pH 2.5 while the rest of them remained viable at levels of 4 to 5 log CFU/ml. However, only strains KE109, KE100, GL70, M104 and GL31 retained viability upon challenging at pH 2.0 in the presence of pepsin (3 mg/ml).
Significance: In conclusion, all seven strains above constitute good probiotic candidates for use in dairy foods. However, additional studies are required to validate their actual ability to colonize the human GI tract to express their potential probiotic capabilities in vivo.