Short communication: Protection of lyophilized milk starter Lactobacillus casei Zhang by glutathione

Lyophilization is considered an effective way to preserve the activity of milk starters, such as lactic acid bacteria, in which proper protective agents play key roles. In this study, Lactobacillus casei Zhang, a probiotic bacterium applied as a milk starter in China, was used to investigate the effects of various cryoprotectants according to cell survival rate and physiological characteristics. The result showed a significant survival improvement to 86.6% when glutathione (GSH) was added as an ideal cryoprotectant. Further study revealed that GSH plays a key role on maintaining higher unsaturation ratio of cell membrane and shorter chain length of saturated fatty acids. In this case, the intact cell structure can be obtained. These findings will contribute not only to deepen the understanding of cells during lyophilization but also to improve the industrial performance of certain milk starters such as L. casei Zhang by application of GSH as cryoprotectant.