Monitoring the growth of Lactobacillus bulgaricus strains with different probiotic activity using physicochemical properties

Abstract

The primary task of probiotics is protection against harmful substances. The most important probioticproducing microorganisms are lactic acid bacteria. Fermented foods are richer in flavour, more shelf-stable, and safer. Yogurts are fermented milk products that contain both Streptococcus thermophilus and Lactobacillus bulgaricus. Their regular consumption is beneficial for the immune system. In our research, we monitored the growth of 15 strains of Lactobacillus bulgaricus with different probiotic activities based on physico-chemical properties. Before the experiment, a calibration test was performed with one sample selected from each group. During the experiment, the pH, cell count, and viscosity were determined from freshly prepared milk products inoculated with activated strains kept for 11 hours at 37 °C. The inflection point of pH curves, pH, cell count, and viscosity values were determined at 4 and 11 hours, and at the inflection point of the pH curve. No significant differences for the 15 strains were found at either sampling time. The average number of colonies of the probiotic samples was the highest, but it was not significantly different from the other two groups. The viscosity of the probiotic strains at 4 and 11 hours was on average a third of the values of the other two groups, with significance. Looking at the viscosity values determined at the time of the inflection point of the pH curve, the non-probiotic strains had the highest and the probiotic strains had significantly the lowest value. Overall, it can be said that viscosity as a physical parameter can be suitable for separating strains showing different probiotic activities.