Stability and functionality of freeze-dried probiotic <i>Bifidobacterium </i>cells during storage in juice and milk

We investigated the stability of differently produced (variables being fermentation time, pH during drying, and cryoprotectant) freeze-dried Bifidobacterium animalis subsp. lactis E-2010 (Bb-12) cells in fruit juice and low-fat milk. In addition, the effect of the food matrix on the acid and bile tolerance of the cells was studied. Cells produced in different ways had comparable stability in milk, whereas in juice, sucrose-protected cells survived better than reconstituted skim milk-protected cells. The acid and bile tolerance was better in cells added to milk compared with those in phosphate buffered saline or juice. Despite good culturable stability in milk the acid and bile tolerance of cells decreased during the storage. Apparently, culturable stability data alone do not give an accurate enough prediction of the probiotic functionality in adverse conditions (e.g. survival in acid and bile stress). When choosing a cryoprotectant for a probiotic also the stability in target food applications should be considered