Calcium ions enhanced freeze-drying and spray-drying resistance of Lactiplantibacillus plantarum LIP-1 by regulation of cell wall surface proteins and related enzymes expression

Abstract

The cell wall of lactic acid bacteria maintain the osmotic pressure inside and outside the cell as well as the inherent morphology of the strain. During the drying process, cell wall is the first site to be damaged. Still, little research has been done to reduce the damage of cell wall during the drying process. Therefore, this study explored the protective effect of calcium ions (Ca2+) on the cell wall of Lactiplantibacillus plantarum LIP-1 during freeze- and spray-drying. Furthermore, the mechanism behind the improved stress resistance of bacteria due to Ca2+ has also been investigated. The results showed that addition of 0.50 mmol/L Ca2+ to the culture medium significantly improved the freeze-drying and spray-drying survival rates of the strain (P < 0.05). It was found that Ca2+ significantly increases the content of surface proteins. Due to the enhanced cell wall proteinase (CEP) activity, the surface proteins are anchored to the cell wall, thereby reducing the cell wall damage in strain during the drying process and improving survival rate during drying and increasing storage stability at room temperature.