Probiotic Lactobacillus casei Zhang improved the properties of stirred yogurt

Probiotic Lactobacillus casei Zhang as an adjunct culture for the production of stirred yogurt was studied. The effects of adding this strain on the rheology, texture, microstructure, and stability of the yogurt were investigated over a 21-day refrigerator storage study using multi-speckle diffusing wave spectroscopy, a single-compression cycle texture test, confocal laser scanning microscopy (CLSM), and other general methods. The content of exopolysaccharides (EPS) was also determined. The probiotic stirred-type yogurt showed 108 CFU/g viable counts of L. casei Zhang, and the high viability rate was maintained throughout the chill storage. The probiotic yogurt containing L. casei Zhang showed a higher elasticity index and lower solid-liquid balance compared with the control group without probiotics, indicating a higher elasticity and the development of a more solid-like gel structure by adding the probiotics. Texture analysis of stirred yogurt showed that the cohesiveness and viscosity index of the probiotic group were significantly higher than that of the control (P<0.05). Meanwhile, significantly more EPS was detected in the probiotic yogurt at the beginning (190 and 67 mg/L for the probiotic and control yogurts, respectively) and after (390 and 140 mg/L for the probiotic and control yogurts, respectively) the storage. CLSM images confirmed that the EPS of the probiotic yogurt were larger in size and interacted with the protein matrix. These results together suggested that adding L. casei Zhang influenced the techno-functional properties of yogurt production positively by increasing the EPS content.