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 delbru eckii ssp. bulgaricus that produce exopolysaccharide or made with a no nproducing strain, with and without addition of commercial stabilizer blends, were compared. A simple test, developed to measure the extensi bility of yogurts, was able to discriminate yogurt made with exopolysa ccharide-producing strains from yogurt made with the nonproducing stra in and to discriminate among yogurts made with different exopolysaccha ride-producing strains. The force required to penetrate the surface of yogurt made with exopolysaccharide-producing strains was less than th at needed for yogurts made with the nonproducing strain. Yogurt made w ith exopolysaccharide-producing strains exhibited less shear thinning than products made with the nonproducing strain. Storage and loss modu li decreased monotonically as strain exceeded 5% for yogurts made usin g 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 s tructural degradation of yogurt made using exopolysaccharide-producing strains in which polymer associated with the casein network prevents disruption of portions of the network.