Effect of exopolysaccharides and proteolytic activity of Lactococcus lactis subsp. cremoris strains on the viscosity and structure of fermented milks

Two exopolysaccharide (EPS)-producing Lactococcus lactis subsp. cremoris strains (B35 and B891) were used to study the effect of the kinetics of EPS production and bacterial proteolytic activity on the structure of milk gels and the viscosity of stirred milk gels. Strains were grown at 20 °C in milk containing either yeast extract or casitone and at 30 °C in either milk alone or milk containing casitone. Lactococcal counts, pH decrease and production and molecular characteristics (molar mass and radius of gyration) of both EPSs were followed during milk fermentation. The level of proteolysis in the fermented milks was determined after 24 h of incubation. The results obtained showed that the yield of EPS and the timing of EPS production during milk-gel formation were the most important factors that influenced the structure of the milk gels and the viscosity of the stirred product. The proteolytic activity of the strains did not seem to play any significant role.