Abstract:

The formulation of cryoprotectants for Lactococcus lactis subsp. cremoris KLDS 4.0326 was optimized by
combined use of single-factor, Plackett-Burman and Box-Behnken response surface designs, and the storage stability at
different temperatures of bacterial powder made with the optimized cryoprotectants was analyzed. The results indicated
that the survival rate was significantly affected by skim milk powder, trehalose and glycerol. By regression analysis of
the obtained experimental data, the optimum cryoprotectant formulation was composed of skim milk powder, trehalose
and glycerol at concentrations of 10.77, 7.81 and 3.31 g per 100 mL water, respectively for maximum cell survival rate of
(87.43±1.62)%, which was close to the theoretical prediction. After the bacterial cells were stored at 4 and 25 ℃ for 12
months, their cell survival rates were 40.63% and 8.67%, respectively. Therefore, the freeze-dried bacterial powder had a
relatively higher storage stability at 4 ℃.

Key words: Lactococcus lactis subsp. cremoris, cryoprotectants, cell survival rate, storage stability, optimization design