Effect of Lactose on Acid Tolerance of Yogurt Culture Bacteria

Abstract

Lactose, the sugar naturally present in milk, provides energy to lactic acid bacteria used in fermented dairy foods. Increasing concentrations of lactose may improve survivability of lactic acid bacteria in the dairy foods and in human gut enhancing their probiotic benefits. Acid tolerance is an important probiotic characteristic. The objective was to determine the influence of lactose on acid tolerance of yogurt starter culture <i> Streptococcus thermophiles </i> ST-M5 and <i> Lactobacillus bulgaricus </i> LB-12. The M 17 broth was used for <i> Streptococcus thermophiles </i> ST-M5 and MRS broth was used for <i> Lactobacillus bulgaricus </i> LB-12 . Lactose was added to both broths at 0% (control), 1%, 3%, and 5% (wt/vol). Both broths were acidified to pH 2.0. Upon sterilizing and tempering, both broths were inoculated. Acid tolerance was determined as viable counts in acidified broths after 120 minutes of incubations. In an incubation period of 2 hours, dilutions were plated every 30 minutes. Three replications were conducted. The highest acid tolerance for <i> Streptococcus thermophiles </i> ST-M5 and <i> Lactobacillus bulgaricus </i> LB-12, was observed in lactose concentration of 3% and 5% (wt/vol).