Effects of exopolysaccharide-producing strains of thermophilic lactic acid bacteria on the texture of stirred yoghurt

Rheological and sensory properties of yoghurts prepared from commercially available cultures that had ropy and non-ropy characteristics were compared. Our results from both instrumental and sensory data suggest that it may not be the amount of polysaccharide that is important to rheological properties, but the type of exopolysaccharide (EPS)-producing strains and consequently the interaction of the polymer with the milk proteins during the fermentation. Data also suggest that the interaction and co-operative growth that occurs in mixed cultures also influences the yield of EPS production in the fermentation, as combining two ropy strains does not lead to an increase in total polysaccharide, although the viscosity can be improved. Texture measurements for viscosity correlated with sensory evaluation of viscosity and with slipperiness.