Synergistic effect of high-pressure thermal sterilization and muramidase on Bacillus subtilis spores: alterations in intrasporal components, inner membrane permeability, and structural integrity

The sporicidal mechanism of high-pressure thermal sterilization (HPTS) combined with muramidase against Bacillus subtilis spores was investigated. Results demonstrated that HPTS at 600 MPa/75°C with 0.3% muramidase achieved a 6.09 log reduction in Bacillus subtilis spores. The combined processing significantly increased the leakage of protein, nucleic acid, and dipicolinic acid, while significantly reducing Na⁺/K⁺-ATPase activity (P < 0.05). Scanning electron microscopy revealed notable morphological changes in spores after combined processing. A significant increase in propidium iodide (PI)-infiltrated spores indicated enhanced spore inner membrane permeability (P < 0.05). molecular composition analysis further showed disordered arrangement of fatty acid acyl chains, structural alterations in nucleic acids and proteins, and increased the peptidoglycan layer flexibility. These findings provided insights into the sporicidal mechanism of HPTS combined with muramidase.