The study aimed to determine the sterilization effect of a combination of high-pressure thermal sterilization (HPTS) and ε-polylysine (PL) on Bacillus subtilis spores. The spores were treated with HPTS (550 MPa at 25°C, 65°C and 75°C) combining with ε-PL at 0.1% and 0.3%. The results showed that HPTS and ε-PL synergistically inactivated the spores. The increased temperature and ε-PL concentration decreased the number of surviving spores, with the maximal inactivation of the spores in the treatment of 550 MPa, 75°C combining with 0.3% ε-PL. The increases in the temperature and ε-PL concentration significantly increased the release of the intracellular components in the spore suspension, with the maximal value for the spores treated with 550 MPa, 75°C and 0.3% ε-PL. The maximal fluidity and permeability of the cell inner membrane were observed in the treatment of 550 MPa, 75°C combining with 0.3% ε-PL. Changes in membrane lipids were detected from 3000 to 2800 cm -1 by Fourier transform infrared spectroscopy. The results may provide new insights into the mechanism by which HPTS and ε-PL synergistically sterilize Bacillus subtilis spores.

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Pressure-assisted thermal sterilization (PATS) is a new technology to inactivate bacterial spores and ensure food safety. Little has been known about the effects of PATS combining with ε-PL on the spore's nucleic acid, enzymes and other key substances. This study aimed to investigate the inactivation effect of PATS combining with ε-PL on the spores of B. subtilis. The spores were treated with pressure 600 MPa at 25 °C, 65 °C and 75 °C, and ε-PL at 0.1% and 0.3%. After treatment, the survival rate of B. subtilis spores, leakage of nucleic acid and protein, the change in the cell membrane ATPase activity, the leakage of dipicolinic acid, and the damage on protein and nucleic acid of the spores were determined. The results showed that PATS combining with ε-PL inactivated more spores, and significantly increased the release of protein and nucleic acid compared to the control. ATPase activity reached the lowest value after the treatment of 600 MPa/75 °C combining with 0.3% ε-PL. The release of dipicolinic acid from the spores was increased by 600 MPa/75 °C combining with 0.3% ε-PL as compared with 600 MPa/75 °C treatment alone. FTIR analysis showed that a combination of PATS with ε-PL changed the spectral features of B. subtilis functional groups of proteins and nucleic acids. The PATS treatments when combined with ε-PL were found to shift the symmetric and antisymmetric stretching vibrational absorption peaks of phosphodiester group in nucleic acid molecules (P=O). This change suggested that the combined treatment denatured nucleic acid. The combined treatment also changed the protein from an ordered state to a disordered state, and decreased protein stability. The results improved our understanding on the principle of spore inactivation by PATS combining with ε-PL.