Rheological Properties of Nonfat Yogurt Stabilized Using Lactobacillus delbrueckii ssp. bulgaricus Producing Exopolysaccharide or Using Commercial Stabilizer Systems

Properties of yogurts made using three strains of Lactobacillus delbrueckii ssp. bulgaricus that produce exopolysaccharide or made with a nonproducing strain, with and without addition of commercial stabilizer blends, were compared. A simple test, developed to measure the extensibility of yogurts, was able to discriminate yogurt made with exopolysaccharide-producing strains from yogurt made with the nonproducing strain and to discriminate among yogurts made with different exopolysaccharide-producing strains. The force required to penetrate the surface of yogurt made with exopolysaccharide-producing strains was less than that needed for yogurts made with the nonproducing strain. Yogurt made with exopolysaccharide- producing strains exhibited less shear thinning than products made with the nonproducing strain. Storage and loss moduli decreased monotonically as strain exceeded 5% for yogurts made using the nonproducing strain. Both moduli decreased monotonically between 5 and 10% strain for yogurt made with the exopolysaccharide-producing strains but exhibited an inflection in the slope between 10 and 100% strain. These data are consistent with a mechanism for shear-induced structural degradation of yogurt made using exopolysaccharide-producing strains in which polymer associated with the casein network prevents disruption of portions of the network.