2.4. Isolation and quantification of exopolysaccharides (EPS)
EPS was isolated from the media according to a method modified
from Liu et al. [5]. Lactobacillus (1 109 CFU/mL) were inoculated
(1%, v/v) into 200 mL of MRS broth supplemented with 2%
glucose at 37 C for 24 h. The bacterial cells were removed by
centrifugation at 6000 g for 10 min. Trichloroacetic acid was
added to the supernatant liquid to a final concentration of 4% (w/v),
and the mixturewas stirred at 4 C for 3 h. The precipitated proteins
were removed by centrifugation at 22,000 g for 30 min. The
supernatant liquid was then concentrated five times by evaporation.
The EPS was precipitated by adding four volumes of 95% cold
ethanol and then stored at 4 C for 24 h, followed by centrifugation
at 22,000 g at 4 C for 20 min. The precipitated EPS was dialyzed
(molecular weight cut-off: 6000 Da to 8000 Da) at 4 C for 48 h and
then lyophilized to obtain a dried powder. The amount of total EPS
was measured using the phenolesulfuric acid method [7].