Screening of heat tolerable lactic acid bacteria and characterization of their β-galactosidases

In this study,heat tolerable LAB strains producing high level β-galactosidase were isolated from chicken feces samples. With 16 S r RNA gene sequence analysis,6 isolated strains were all identified as Lactobacillus reuteri. All β-galactosidases from the isolated L. reuteri strains had the same optimum p H of 6.5.After incubating for 1 h at 55 ℃,51.2% of β-galactosidase of strain MF1567 activity was retained. The amino acid sequence analysis showed that 22 amino acid residues of β-galactosidase Lac Z were substituted. The secondary protein structure was further predicted and Lac Z had a relatively higher degree of α-helix(26.5%),which might contribute to the heat stability of β-galactosidase Lac Z from L. reuteri MF1567.