Surface characteristics and proteomic analysis insights on the response of Oenococcus oeni SD-2a to freeze-drying stress

Oenococcus oeni (O. oeni) induces malolactic fermentation to improve wine quality. However, the molecular basis of mechanisms involved in its freeze-drying resistance remains unclear. In this work, O. oeni SD-2a without freeze-drying (No-FD), with freeze-drying (FD) and freeze-drying with monosodium glutamate (MSG) (FD-MSG) were investigated. Flow cytometry results showed severe cell damage in FD cells and less membrane transmissibility in FD-MSG cells. Meanwhile, extracellular polymeric substances (EPS) were detected in FD and FD-MSG cells by scanning electron microscopy. Bioinformatic analysis revealed that varying proteins were involved in carbon, lipid and nucleic acids metabolism, stress response, oxidoreductase activity and signal sensing. Among the identified proteins, the highlighted proteins were those involved in polysaccharides production and signal sensing for freeze-drying resistance and cyclopropane fatty acid metabolism for MSG addition.