Abstract: In order to explore the fermentation and storage characteristics of set yogurts made from sheep milk and cow milk, their pH, titratable acidity, texture properties, taste characteristics, viable bacterial population and sensory scores were determined by a pH meter, an acidity titrator, a texture analyzer, an electronic tongue, viable counting and sensory evaluation, respectively. During the fermentation process, the two yogurts showed the same pH trends. The pH decreased slowly in the first 2.5 hours, then dropped rapidly, and finally kept declining slowly from 0.5 h before coagulation until the completion of coagulation. The fermentation was completed after 5 and 4.5 h for fermented sheep milk and cow milk, respectively. During 24 days of storage at 4 ℃, the pH of both fermented milks dropped gradually, and fermented cow milk decreased more than did fermented sheep milk. The titratable acidity of fresh sheep milk was higher than that of fresh cow milk, and the titratable acidity of fermented sheep milk was similarly higher than that of fermented cow milk at the end of fermentation. Moreover, fermented sheep milk containing Lactobacillus paracasei subsp. paracasei Zhang (YSM) and that containing L. bulgaricus and Streptococcus thermophilus (JDM) had higher hardness and consistency, and significantly higher cohesiveness and viscosity than did fermented cow milk containing L. bulgaricus and S. thermophilus (JDN). The type of milk was found to be the main factor that affects the hardness, consistency, viscosity and viscosity of yogurt, while the addition of probiotic L. paracasei subsp. paracasei Zhang had little influence on any of these indicators. The results of electronic tongue revealed that the taste sensation value for richness of fermented sheep milk was significantly higher than that of fermented cow milk, while the sourness sensation value was lower that of fermented cow milk. There was no significant difference in the sensation scores for sweet, bitter, salty, astringent or umami taste between the two fermented milks. The overall sensory score of fermented sheep milk was higher than that of fermented cow milk, and there were differences in the sensory scores for taste, texture, and liking degree but not color or smell between them. Total viable bacterial count gradually declined during the 21-day storage period for all fermented milk samples. YSM showed the highest viable bacterial count and its value on day 21 of storage was over 10- and 100-fold higher than that of JDM and JDN, respectively. In conclusion, L. paracasei subsp. paracasei Zhang can be used as a candidate starter culture in combined with the traditional yogurt starter cultures of L. bulgaricus and S. thermophilus for the production of set yogurt made from sheep milk for improved functional value.

Key words: sheep milk; set yogurt; Lactobacillus paracasei subsp. paracasei Zhang; texture; taste;?radar chart