Effect of Fermentation with Single and Co-culture of Lactobacillus bulgaricus and Streptococcus thermophilus on the Quality of Yogurt

In order to investigate the effects of fermentation with single and co-culture of Lactobacillus bulgaricus and Streptococcus thermophilus on the quality of yogurt, the fermentation characteristics, sensory features, rheology and texture of yogurt produced by the above two fermentation approaches were tested. The results showed that the curdling time of co-culture fermented yogurt was 8 h, which was shorter than that of single-strain fermented yogurt, and reached the end point of fermentation at 70 °T earlier. Sensory evaluation evaluated that the scores of co-culture fermentation yogurt were higher than that of single culture yogurt. Moreover, the ratio of Lactobacillus bulgaricus and Streptococcus thermophilus was 3:7 with the highest score. The measurement results of rheological properties showed that the apparent viscosity of co-culture fermented yogurt was 0.4~0.5 Pa·s lower than that of single-bacteria fermented yogurt of 1.6~1.9 Pa·s. As for texture analysis, the hardness, viscosity and absolute value of cohesiveness of co-culture fermented yogurt were significantly lower than that of single culture yogurt (P<0.05). The data of electronic nose showed that the odor of co-culture fermented yogurt was stronger than that of single bacteria fermented yogurt. In addition, electronic tongue test showed that the co-culture fermented yogurt exhibited more balanced in terms of different tastes. Electronic nose and electronic tongue could effectively distinguish the difference between single and co-culture fermented yogurt through principal component analysis. Based on the above results, the taste and flavor of co-culture fermented yogurt are better than that of single bacteria fermented ones.