Characterization of Key Lipid Components in the Cell Membrane of Freeze-Drying Resistant <i>Lacticaseibacillus paracasei</i> Strains Using Nontargeted Lipidomics

Lactic acid bacteria (LAB) are usually freeze-dried into powder for transportation and storage, with the bacterial membrane playing a crucial role in this process. However, different strains exhibit different levels of freeze-drying resistance in their cell membranes. In this study, <i>Lacticaseibacillus paracasei</i> (<i>L. paracasei</i>) strains 1F20, K56, and J5, demonstrating survival rates of 59.51, 25.86, and 4.05% after freeze-drying, respectively, were selected. The membrane structure and composition of these strains were subsequently analyzed. Bacterial live/dead staining results indicated that strain 1F20 maintained the highest membrane integrity after drying. Nontargeted lipidomics analysis revealed six differential lipid species that differed in membrane lipid compositions. KEGG functional enrichment analysis revealed 13 significantly different pathways, with glycerophospholipid metabolism being the most critical. This study explored the membrane composition of <i>L. paracasei</i> at the cellular level and identified key lipid species associated with freeze-drying resistance, providing a reference for screening highly resistant strains.