The effect of rehydration media, freezing temperature, and combinations of cryoprotectants on the survival rate of freeze-dried lactic acid bacteria

Freeze-drying is currently a commonly drying technique for lactic acid bacteria (LAB) used in vegetable fermentation. The objective of this study is to investigate the effect of freezing temperature, rehydration media, and combinations of cryoprotectants on the survival rate of freeze-dried LAB (L. plantarum OMCb1-1 and L. pentosus OP1-1) isolated from fermented vegetables in Cambodia. First, pre-freezing was performed under two conditions, –20°C and –80°C for 24 h, continuing with primary drying (–36°C for 24 hours) and ending with secondary drying (–42°C for 2 hours). To determine the viability of the LAB after freeze-drying, different rehydration media were used. The different cryoprotective agents were used alone or in combination to protect the bacteria cells. The best protectant for obtaining the highest viability after freeze-drying was 10% skim milk + 8% sucrose + 1.5% gelatin (pre-freezing at –80℃) with a maximum viability of 94.75% and 93% for L. pentosus OP1-1 and L. plantarum OMCb1-1, respectively. Their highest survival rates were obtained when rehydrated with MRS broth (63%) and 10% skim milk (94%), respectively. After freeze-drying, their residual moisture contents were between 2.03% and 9.3821%, and the water activity was between 0.182 and 0.4847, depending on the nature of the protective agents.