Abstract:

Two strains of lactic acid bacteria were isolated from naturally fermented yogurt. The 16S rDNA sequence analysis
indicated that the two strains were Lactobacillus plantarum SN1 and Lactobacillus rhamnosus SN6. These strains were studied
for growth curve, acid production rate, acid and bile salt tolerance. Both of them reached a logarithmic growth phase after 2 h
and a stable period after 16 h with OD 600 nm values of 8.47 and 7.43, respectively. The pH value dropped to 4.2 at 8 h and 3.3
at 48 h. L. plantarum SN1 and L. rhamnosus SN6 had strong resistance to acid, and the relative OD 600 nm value was 49.29%
and 47.14% at pH 4.0 after 16 h of culture, respectively. After being cultured for 16 h at a bile salt concentration of 0.3 g/L,
the relative OD 600 nm values of L. plantarum SN1 and L. rhamnosus SN6 were 57.7% and 69.48%, respectively, compared
to 48.22% and 29.56% when the concentration of bile salt was 0.6 g/L. These results show that both L. plantarum SN1
and L. rhamnosus SN6 are probiotic strains with strong growth performance, acid production and tolerance to acid
and bile salt.

Key words: lactic acid bacteria, acid and bile salt tolerance, 16S rDNA sequence analysis