Research for the yeast inhibiting ability of sorbic acid and cycloheximide applied to the quantitative analysis of Lactobacillus spp.

The ability of sorbic acid and cycloheximide to inhibit yeast was investigated on nine yeast strains isolated from different sources. Sorbic acid was added to MRS agar at two concentrations 0.01 g/L (TCVN 5522:1991) and 1.4 g/L (TCVN 7906:2008). The results showed, at both concentrations; the inhibitory effect of sorbic acid on yeast strains was weak. In contrast, the survey results of MRS agar supplemented with cycloheximide with concentration ranges of 0.02; 0.04; 0.06; 0.08; and 0.10 g/L were inhibited yeast strains. The performance testing of MRS agar supplemented with 0.05 g/L of cycloheximide tested with productivity ratio (0.7 ≤ PR ≤ 1.4) and selectivity factor (SF ≥ 2) according to ISO 11133. Therefore, we determined ability to inhibit yeast from cycloheximide was higher than sorbic acid and suggested using MRS agar-supplemented cycloheximide with 0.05 g/L, pH 6.2 (after autoclaving) to establish the quantitative analysis of Lactobacillus spp. by the pouring plate technique, incubated at 37oC ± 1oC for 72 ± 3 hours. In addition, the research results contribute to improving the quantitative analysis of Lactobacillus spp. in order to ensuring the validity of results and providing scientific evidence for decisions on management of effective probiotic quality in Ho Chi Minh City, Vietnam.