Effect of cryoprotective agents on survival and ss-galactosidase activity of Lactobacillus acidophilus and Streptococcus thermophilus during freeze-drying

摘要

Freeze drying is an important process for starter culture preservation. In the present investigation, effect of single as well as mixed cryoprotective (CP) agents was evaluated on the stability of two strains of lactic acid bacteria e.g. Lactobacillusacidophilus and Streptococcus thermophilus in terms of survivability and enzymatic activity during freeze-drying process. The CP agents used were 10% lactose, 10% sucrose, skim milk containing 0.5% yeast extract and 1 % sorbitol (SYS) and skim milk with7% sucrose, 1 M mono-sodium glutamate and 1.5% gelatin (SSMG). After concentration, the cells were mixed with an equal volume of each cryoprotectant. Following freeze drying, viability of dried cultures was assessed by enumeration of colony forming units. Among different CP agents tested, the mixed cryoprotective agents such as SSMG provided higher survivability to L. acidophilus (95.1 %) and S. thermophilus (89.9%) culture. No significant protective effect was observed on ss-galactosidase activity after the drying process. All CP agents exhibited 0.04-0.055 units of enzyme activity. This study proves the importance of mixed protective agents to maximize stability of L acidophilus and S. thermophilus after freeze-drying, and the dried culture could beutilized as a starter in dairy industry for manufacture of fermented milk products.