Physical, microbiological and rheological properties of probiotic yogurt supplemented with grape extract

In this study, yogurt was supplemented with 1.5 and 3.0 g L^-1 of grape extract, inoculated culture containing Streptococcus thermophilus, Lactobacillus bulgaricus, Lactobacillus acidophilus and Bifidobacterium bb12 bifidum, fermented and stored at 4 °C. Acid production, microbial growth, gel strength, syneresis, rheological and sensory properties were studied. An increase in grape extract concentration extended fermentation time. Bacterial strains were found in at least 109 CFU100 g^-1 of yogurt showing the possibility of probiotic yogurt production with grape extract. Gel strength decreased with increasing concentration of grape extract while syneresis increased. The addition of grape extract changed the dilatant behavior to a pseudoplastic behavior, decreased yield stress, whereas k values increased. Sensory attributes (color, flavor, taste, texture and appearance) didn't differ significantly.