Biopolymers from Lactic Bacteria: Evaluation of Functionality in a Gastric System In Vitro

GERBINO, ESTEBAN; MOZZI, FERNANDA; FONT DE VALDEZ, GRACIELA; TORINO, MARÍA INÉS

San Miguel de Tucumán, Tucumán, Argentina

Simposio; II Simposio Internacional de Bacterias Lácticas. Primer Encuentro Red BAL Argentina; 2006

Centro de Referencia para Lactobacilos (CERELA) - CONICET

The exopolysaccarides (EPS) of lactic acid bacteria (LAB) have biotechnological interest because the multiple properties derived from their structural characteristics: monomer composition, glycosidic linkages, molecular mass and type of EPS (capsular or slime). Special relevance presents the antiulcer or protective effect on gastric mucosae, associated to certain EPS from this bacterial group. In this work the effect of biopolymers produced by Lactobacillus casei CRL 87 and Streptococcus thermophilus CRL 1190 was evaluated during simulation of the gastric transit. Thereby an in vitro gastric model containing saliva and artificial gastric juice was developed and standardized. The EPS+ strains (CRL 87 and CRL 1190) and their isogenic EPS- mutants (M7 and M16, respectively) were cultivated in 10% reconstituted skimmed milk until coagulation (pHf = 4.40). These fermented milks were subject to gastric digestion in the developed model during 2 h at 37°C, adjusting pH gradually until 3. The viability (cfu/ml) and the cellular metabolic activities [enzymes b-galactosidase (b-GAL) phospho-b-GAL and lactate dehydrogenase (LDH)] were evaluated. The gastric treatment affected the survival and microbial physiology of both EPS+ and EPS- strains, with some differences according to the bacterial genera. The enzyme activity was the most affected parameter; residual activity being only detectable in M16 mutant (4.5 and 2.2% for b-GAL and LDH, respectively). The cell counts were 14% (CRL 1190) and 8% (M16) lower than the non-treated controls. L. casei strains were more resistant than S. thermophilus since the survival (93% for CRL 87 and M7) and the enzyme activities were similar to those observed for control samples. Nevertheless, a 16% decrease in b-GAL level was observed for the mutant M7 strain. The enzyme phospho-b-GAL (not detected in S. thermophilus strains) showed higher activity than b-GAL in both wild type CRL 87 and mutant M7. Preliminary HPLC assays showed a decrease in the molecular mass of EPS after treatment; this degradation would be associated to the gastric juice and the low pH reached. Results obtained in this work show that the biopolymers of the evaluated LAB strains have a limited protective role under harmful environmental conditions such as the prevailing ones in the stomach.