Study on the preparation conditions of a freeze-dried starter for Lactobacillus casei LC-15

Probiotic starter culture plays an important role in developing probiotic yoghurt or fermented dairy products.In this paper,the proper cryoprotectant for the cholesterol-reducing probiotic strain Lactobacillus casei LC-15 was studied.The best cryoprotectant was obtained using orthogonality test: NFM powder 100 g/L,maltodextrin 100 g/L,L-glutamine10 g/L,glycerol 30 mL/L,trehalose 150 g/L.The survival rate of the freeze-dried starter reached 82.2%,and the viable counts was 4.4×1010 g-1.With the optimization of the freeze-dried starter preparation conditions,we obtained the maximum starter survival rate(84.8%) and the maximum viable count(4.9×1010 g-1) by preincubating suspended culture at 37 ℃ for 60 min,and then freezing at-40 ℃ for 3 h.