The postacidification evaluation of Lactobacillus delbrueckii subsp.bulgaricusin yogurt

Lactobacillus delbrueckii subsp.bulgaricus is the key bacteria involved in the postacidification of yogurt.To ascertain the extent of postacidification,in this study,yogurts were fermented by 6 Lactobacillus delbrueckii subsp.bulgaricus stains from different dairy products or starters to analyse the fermentation properties.In the process of storage,the pH value,titratable acidity and viable count were determined to evaluate the postacidification of the yogurts.Among the tested strains,the curd time of L.b-TX and L.b-MH was longer and the extent of postacidification was higher,so they were not good strains of yogurt starter.The fermentation properties and the extent of postacidification were better in the other strains.This work will establish a basis for breeding of Lactobacillus delbrueckii subsp.bulgaricus,and will promote our own researches on yogurt starter at the same time.