Abstract: The effect of the exopolysaccharide (EPS) from Lactobacillus plantarum YW11 on microbial growth, acid production rate and microrheological properties during yogurt fermentation and the texture and flavor characteristics of the final product was studied. The results showed that there was no significant effect of different concentrations (0.05, 0.15 and 0.25 mg/g) of the EPS on the growth of Lactobacillus bulgaricus and Streptococcus thermophilus or acid production rate during the fermentation process. Addition of the EPS had different effects on the elasticity index (EI), microviscosity index (MVI) and fluidity index (FI) of yogurt during fermentation; with increasing addition of the EPS, the EI decreased gradually, the MVI increased, whereas the FI did not change significantly. The water-holding capacity of yoghurt could be improved by adding different amounts of the EPS, reaching the maximum of 57.93% at an EPS concentration of 0.25 mg/g. With increasing addition of EPS, the hardness of yoghurt decreased to the lowest value of 10.08 g, the viscosity increased to the highest value of 9.57 g, while the cohesiveness changed little, varying between 0.45 and 0.48. Addition of EPS enhanced the cross-linked structure of proteins in yoghurt, made the protein particles smaller, and produced larger pores in the network structure. Addition of an appropriate amount of the EPS could promote the formation of flavor compounds such as aldehydes, acids and esters. The results of this study will be helpful for further understanding the effect of L. plantarum EPS on the processing characteristics of yogurt, and the application of the EPS to improve yoghurt quality.

Key words: exopolysaccharide; yoghurt; microrheology; texture; flavor