Mechanisms Involved In Synergistic Inactivation Of Bacterial By High Hydrostatic Pressure And Nisin

High Hydrostatic Pressure is a new type of non-thermal sterilization technology. It has been widely concerned because its good sterilization and tiny bad effect to the food texture. HHP could be synergized with Nisin in neutral food system to achieve commercial sterilization. HHP has a synergistic inactivation with Nisin. The study was to investigate the synergistic effect at molecular level alongside ultramicroscopic structure. It would form the theoretical base on the application of HHP in low acid food system.Five bacterial stains which are common found in food system were selected. They were subjected to HHP (100-500 MPa) alone and in combination with Nisin. The sterilization curve illustrated that Nisin is effective to Gram-positive bacteria but ineffective to Gram-negative bacteria. When the pressure was above 200 MPa, Nisin would exist a synergistic effect to Gram-negative bacteria.The integrity and liquidity of the cell membrane is an important factor to maintain its cell viability. The membrane permeability and cell nucleic acid substance leakage of three types of stains were studied. The result illustrated the combination of HHP and Nisin could increase the membrane permeability by 10%-60%. Nucleic acid substance leaked from the cells with the HHP-Nisin treatment. The physical state of membrane phospholipid molecules changed from liquid crystalline to gel state with a decrease in membrane fluidity.The secondary structure of cell protein was changed by the synergistic effect. HHP decreased the a-helix while increased theβ-turn structure. When in combination of HHP and 200 IU/mL Nisin, p-turn structure increased from 11.9% to 13.9%.Flow cytometric date showed when in combination with HHP treatment, Nisin mainly damaged the esterase activity. Nisin helps to inactivate the cell esterase, thus change the sublethal bacterial to damaged bacterial cells. Finally, the ultramicroscopic structure demonstrated that cell content leaked owing to the synergistic effect.The above research showed Nisin is an effective bactericide when combined with HHP in low acid food and that the two inactivation methods have a synergistic effect.