Characterization of freeze-dried Lactobacillus acidophilus in goat milk powder and tablet: Optimization of the composite cryoprotectants and evaluation of storage stability at different temperature

Probiotic application in food industry remains a challenge in decades because of bacterial loss in viability during powder manufacture and storage. Well-designed cryoprotectants and storage condition are crucial for successful probiotic application. In this study, survival of Lactobacillus acidophilus with composite cryoprotectants was investigated during freeze-drying and subsequent storage at different temperature (-18 degrees C, 4 degrees C and room temperature-25 degrees C). The composite cryoprotectants were optimized to be trehalose of 13%, Na2HPO4 of 0.33%, lactose of 7.5% and skim milk powder of 21% with the aid of response surface method. The survival rate of freeze-dried L. acidophilus increased to (93.9 +/- 0.12) % in comparison to control (36.6 +/- 0.08) %. Furthermore, freeze-dried L. acidophilus powder was applied in two dairy forms (goat milk powder and tablets) and cell viability was monitored during 180 days of storage. The freeze-dried powder exhibited better stability in goat milk powder than that in tablets. The cell survival in goat milk powder and tablets was higher at low temperature ( -18 degrees C and 4 degrees C) during storage. Our finding provided a formulation of composite cryoprotectant with great protective effect to probiotic cells during freeze-drying. The freeze-dried powder showed potential application to functional dairy production in relative food industry.