Influence of added lactose on some probiotic properties of yogurt culture bacteria
Lactose is a source of energy for lactic acid bacteria in dairy fermented products. Acid tolerance and bile tolerance are important probiotic properties. The influence of lactose on acid tolerance and bile tolerance of yogurt culture bacteria is not known. The objective was to determine the influence of lactose on acid and bile tolerance of yogurt starter culture Streptococcus thermophilus ST-M5 and Lactobacillus bulgaricus LB-12. Acid tolerance was conducted on pure cultures of S. thermophilus in M17 broth at pH 2.00 and L. bulgaricus in MRS broth at pH 2.00 both at 30 minutes intervals for 2 hours of incubation. Bile tolerance of pure cultures was determined using MRS-THIO broth with 0.3% oxgall for L. bulgaricus and MRS broth with 0.3% oxgall for S. thermophilus. Dilutions were plated every hour for 12 hours. Three replications were conducted. Data were analyzed using Proc Mixed model of SAS® 9.3 program. Significant differences between means were analyzed at α = 0.05 using Tukey’s adjustment. With use of lactose at 3 or 5% (w/v), the Streptococcus thermophilus ST-M5 had significantly higher acid tolerance than control at 120 min. In presence of lactose at 3 or 5% (w/v), the Lactobacillus bulgaricus LB-12 had significantly higher acid tolerance than control at 60, 90 and 120 min. Lactose, when used at 5% (w/v), significantly improved bile tolerance of L. bulgaricus compared to control. With use of lactose at 1% (w/v), S. thermophilus had significantly higher bile tolerance compared to control at 2 h of incubation. Use of lactose at 5% (w/v), favorably influenced acid tolerance of S. thermophilus and the bile tolerances of S. thermphilus and L. bulgaricus.
Keywords: added lactose, acid tolerance, bile tolerance, starter culture