Screening and Selection of 2-Branched (1,3)-β-D-Glucan Producing Lactic Acid Bacteria and Exopolysaccharide Characterization

The ability to produce a 2-branched (1,3)-beta-D-glucan was screened in 147 lactic acid bacteria strains recovered from cider. Among them, 32 identified as Pediococcus parvulus exhibited a ropy character and were PCR positive for the presence of the gtf gene, related to the synthesis of the beta-glucan. Half of the strains produced more than 100 mg L-1 of exopolysaccharide (EPS). H-1 NMR spectra of the crude EPSs were identical to that previously described for P. parvulus 2.6, indicating that all are 2-branched (1,3)-beta-D-glucans. The EPSs from two of the isolates were subjected to acid hydrolysis and methylation analysis, confirming the NMR results. Size exclusion chromatography (SEC) showed in all crude EPSs the presence of two different molecular mass fractions of about 10(7) Da and 10(4) Da, whose relative proportions varied among strains. EPS amounts and concentrations of high molecular fraction are linearly correlated. Intraspecific diversity of isolates was determined by RAPD profiles. Based on genotypic and phenotypic characteristics, two strains were selected to be further studied as probiotics.