The exopolysaccharides (EPS) produced by lactic acid bacteria (LAB) and released into fermented milk play a protective role from stress factors as well as improve emulsifying and thickening properties of the product, reduce syneresis, and increase elasticity. Here we report the relationship between the properties, composition, and microstructure of EPS produced by six different strains of lactobacilli (L. bulgaricus and five strains isolated from silage). The presence of fructose together with negative-charged uronic acid was found to play a significant role in changing the EPS properties. Thus, the increased fraction of rhamnose and arabinose and a decrease in xylose leads to compaction of the EPS, decreased porosity and increased both OH- and superoxide scavenging and Fe-chelating activities. By contrast, increased xylose and low rhamnose and arabinose apparently leads to loss of large aggregates and high DPPH activity and FRAP. The high content of glucose, however, provides the formation of large pores. The increased fructan fraction (69.9 mol%) with a high fraction of galacturonic (18.2 mol%) and glucuronic acids (6.7 mol%) apparently determines the highly porous spongy-folded EPS microstructure. Taken together, our results indicate that both the quantitative characteristics of the individual components of the fraction and the structural features of EPS are important for the antioxidant potential of fermented milk and depend on the strain used for milk fermentation, suggesting the advantage of a multicomponent starter to achieve the optimal beneficial properties of fermented milk.

A positive effect of flaxseed mucilage (FSM) addition (at concentrations of 0.1, 0.2, and 0.4%) to MRS and milk whey nutrient medium on the survival, auto-aggregation, hydrophobicity, adhesive, and antioxidant properties of L. bulgaricus, L. fermentum AG8, and L. plantarum AG9 was shown. It was found that the AG 8 strain became less sensitive to 7% NaCl concentrations (the cell survival rate in the experiment with 0.4% flaxseed mucilage increased by 10% compared to the control). Cultivation in the presence of FSM led to an increase in auto-aggregation, especially in the case of AG8 (from 60 to 85%) and AG9 (from 50 to 80%) strains, and an increase in hydrophobicity was seen: for L. fermentum AG8, it was from 30% to 62–72%, for L. fermentum AG9 from 30% to 35–42%, and for L. bulgaricus from 20% to 30%. The adhesive properties of the L. fermentum AG8 and L. plantarum AG9 cells increased from 0.472 to 1 nN (nanonewton) and from 0.630 to 2.5 nN, respectively. The presence of flaxseed mucilage increased the total phenolic content in cell-free supernatants after 48 h of cultivation. The concentration of 0.1–0.2% FSM increased the OH-scavenging activity of milk whey nutrient medium cell-free supernatants of strains AG8 and AG9 by 7–10%. Flaxseed mucilage can serve as a promising bioactive additive that elevates antioxidant activity, increases the resistance and survival of Lactobacillus cells in the gastrointestinal tract, and leads to the synthesis of lipase and α-glucosidase inhibitors. The co-culture of these lactic acid bacteria in the presence of FSM and milk components in the form of whey leads to the synthesis of lipase and α-glucosidase inhibitors more than the culturing on de Man, Rogosa, and Sharpe broth.

Milk fermentation by lactic acid bacteria both enhances its nutritional value and provides probiotic strains to correct the intestinal microflora. Here, we show the comparative analysis of milk fermented with the new strain, Lactiplantibacillus plantarum AG10, isolated from silage and the industrial strain Lactobacillus delbrukii subs. bulgaricus. While the milk acidification during fermentation with L. plantarum AG10 was lower compared with L. bulgaricus, milk fermented with L. plantarum AG10 after a 14-day storage period retained a high level of viable cells and was characterized by an increased content of exopolysaccharides and higher viscosity. The increased EPS production led to clot formation with higher density on microphotographs and increased firmness and cohesiveness of the product compared with L. bulgaricus-fermented milk. Furthermore, the L. plantarum AG10-fermented milk exhibited increased radical-scavenging activity assuming lower fat oxidation during storage. Taken together, these data suggest that L. plantarum AG10 seems to be a promising starter culture for dairy products with lowered levels of lactic acid, which is important for people with increased gastric acid formation.