Exopolysaccharide-producing Lacticaseibacillus paracasei strains isolated from kefir as starter for functional dairy products

Abstract

Exopolysaccharides (EPS) produced by lactic acid bacteria are molecules of great interest for the dairy food industry. Lacticaseibacillus paracasei CIDCA 8339, CIDCA 83123, and CIDCA 83124 are potentially probiotic strains isolated from kefir grains whose EPS-production on MRS broth is dependent on incubation temperature. The aim of the present work is to evaluate the effect of fermentation temperature on the characteristics of EPS produced in milk by L. paracasei strains and the consequent impact on the rheological properties of the fermented products. Additionally, the protective effect of these EPS against Salmonella infection was evaluated in vitro. Acid gels with each strain were obtained by milk fermentation at 20°C, 30°C, and 37°C evidencing for all the strains a reduction in growth and acidification rate at lower temperature. Lacticaseibacillus paracasei CIDCA 83123 showed low fermentation rate at all temperatures requiring between 3 and 8 days to obtain acids gels, whereas CIDCA 8339 and 83124 needed between 24 and 48 h even when the temperature was 20°C. Fermentation temperature led to changes in crude EPS characteristics of the three strains, observing an increase in the relative amount of the high molecular weight fraction when the fermentation temperature diminished. Additionally, EPS₈₃₁₂₄ and EPS₈₃₁₂₃ presented modifications in monosaccharide composition, with a reduction of rhamnose and an increase of amino-sugars as temperature rise. These changes in the structure of EPS₈₃₁₂₄ resulted in an increase of the apparent viscosity of milks fermented at 20°C (223 mPa.s) and 30°C (217 mPa.s) with respect to acid gels obtained at 37°C (167 mPa.s). In order to deepen the knowledge on EPS characteristics, monosaccharide composition of low and high molecular weight EPS fractions were evaluated. Finally, it was evidenced that the preincubation of intestinal epithelial cells Caco-2/TC-7 with EPS₈₃₃₉ and EPS₈₃₁₂₄ partially inhibit the association and invasion of Salmonella. In light of these results, it can be concluded that the selection of the EPS-producing strain along with the appropriate fermentation conditions could be an interesting strategy to improve the technological properties of these L. paracasei fermented milks with potential protective effects against intestinal pathogens.

Keywords: Lacticaseibacillus paracasei; exopolysaccharides; fermented milks; functionality; kefir.

Figure 1

Acidification kinetics of Lacticaseibacillus paracasei CIDCA 8339, CIDCA 83123 and CIDCA 83124 in milk at 20°C (), 30°C (), and 37°C (). Dotted line indicates the pH selected for characterization of fermented milks.

Figure 2

Flow curves (A) and apparent viscosity at 300 s⁻¹ (B) of milks fermented with L. paracasei CIDCA 8339, CIDCA 83123, and CIDCA 83124 at 20°C (), 30°C (), and 37°C (). Significant differences ** p < 0.01, *** p < 0.001.

Figure 3

Monosaccharide composition of EPS produced by L. paracasei CIDCA 8339, CIDCA 83123 and CIDCA 83124 in milk at 20°C, 30°C, and 37°C. Standard deviation in monosaccharide composition was between 0.2 and 4 depending on the percentage of each monosaccharide.

Figure 4

High-performance size exclusion chromatograms of EPS isolated from milk produced by L. paracasei CIDCA 8339 and CIDCA 83124 at 20°C, and monosaccharide composition of the corresponding high and low molecular weight fractions. AU: arbitrary units. Standard deviation in monosaccharide composition was between 0.4 and 4 depending on the percentage of each monosaccharide.