Abstract:
Two bacteriocin-producing strains of lactic acid bacteria namely: Pediococcus acidilactici AA5a and Lactobacillus plantarum BS, were exposed to bile (0.3% Oxgall) and low pH (2 and 3) conditions in de Mann, Rogosa and Sharpe (MRS) media and simulated gastric juice (pH 2 and 3) and intestinal fluid (pH 7.2), in comparison with Lactobacillus paracasei 1Y9 - a strain isolated from a commercial probiotic drink. These tests simulate the gastro-intestinal tract where they will pass through when ingested as probiotic supplements. Results showed that all strains have good tolerance in bile-treated MRS medium (pH 6.3) for 5 hour (h) but after 24 h there was a decrease of 1.5, 3.0 and 4.5 log CFU/ml for AA5a, BS and 1Y9, respectively. In MRS medium adjusted to pH 3, all strains showed good tolerance after 5h of treatment but not at pH 2 where only strain BS survived (log 2.5 CFU/ml from an initial of log 7.7 CFU/ml). Likewise, only strain BS withstood the combination of pH 3 and bile treatment (5 log CFU/ml cells remained viable after 5 h). The results for artificial gastric juice (AGJ) and simulated intestinal fluid (S1F) affirmed their ability to tolerate low pH. The observations were consistent in the count of viable cells for BS and 1Y9 and 40% viability for AA5a even after treatment at pH 3 for 3 h in AGJ and for another 3 h in S1F. On the other hand, treatment at pH 2.0 for 3 h in AGJ and subsequent incubation for 3 h in S1F inhibited growth of AA5a but considerable 1Y9 and BS cells remained viable, i.e., decrease of only 1 and 3 log units, respectively.
