Characterization of newly isolated thermotolerant lactic acid bacteria and lactic acid production at high temperature

This study aimed to select a number of thermotolerant lactic acid bacteria for lactic acid fermentation at high temperature, and to identify these LAB strains by using 16S ribosomal RNA sequences. The fermentative ability of 16 selected strains was examined at different temperatures (37°C, 39°C and 41°C), of which, the lactic acid concentration produced by these LAB strains at 37°C ranged from 6.0 g/L to 14.1 g/L. Ten LAB strains (L2, L7, L9, L11, L21, L26, L30, L36, L37 and L52) with effective lactic acid fermentation at 37°C were chosen for identification. The selected strains were characterized as L. plantarum, L. casei, L. acidophilus, and L. delbrueckii, L. casei L9 was the superior lactic acid producing strain at both 39°C (18.9 g/L) and 41°C (18.0 g/L). Based on statistical analysis, appropriate conditions for lactic acid production by L. casei L9 at 39°C were defined as follows: pH 6.51, glucose concentration 6% (w/v) and inoculation level 2.37% (v/v). At these conditions, the validated lactic acid concentration and the yield were recorded at 21.15 g/L and 80.84%, respectively.