Standardization of lyophilization medium for Streptococcus thermophilus subjected to viability escalation on freeze drying

Abstract

The objective of the present study is to develop a lyophilization medium for Streptococcus thermophilus (NCIM 2904) as the industrial exploitation of this bacterium totally depends upon preservation and lyophilization protocols. Protective effect of 18 compounds were observed individually and in combinations with different sugars, sugar alcohols, polymers, protein concentrates and buffers. Among all the protectants tested, ammonium citrate (1% w/w), K2HPO4 (1% w/w) and KH2PO4 (1% w/w) provided lowest protection to these bacterial cells while 10% (w/w) sodium caseinate, whey protein concentrate, sweet whey powder, and skim milk showed significant results in viability escalation. Survival in carbon sources like lactose, sucrose and maltodextrine was also favored maximally. Combination of sodium caseinate 10%, skim milk 5%, sucrose 5%, lactose 5% and mono sodium glutamate 1% in distilled water in ratio of 1:5 with S. thermophilus showed survival percentage of 96%.

Keywords

• lyophilization, freeze drying, S. thermophilus, lyoprotectant, viability