Effect Of Ultra High Pressure Treatment On Listeria Monocytogenes And Application In Shrimp Meat Sterilization

In the present study, the potential mechanism of ultra high pressure (UHP) combined with lysozyme or nisin on inactivation Listeria monocytogenes was explored. We investigated the combination effect of UHP with lysozyme or nisin on the morphology and microstructural damage on Listeria monocytogenes. Then the effect of combination of UHP with lysozyme or nisin on Listeria monocytogenes in shrimp meat, as well as the qualities of shrimp meat were studied. At the same time the shelf life of UHP combined with lysozyme or nisin treated shrimp meat was investigated.The effect of UHP (100-500MPa) combined with lysozyme (2-6mg/mL) or nisin (100-200IU/mL) treatment on the survival rate, the microstructural damage, membrane permeability, Na+/K+-ATPase activity of Listeria monocytogenes were studied. No viable cell was detected after300MPa combined with6mg/mL lysozyme or200IU/mL treatment. The structure changes showed that the cell wall and membrane was seriously damaged after UHP combined with lysozyme or nisin treatment. The cell membrane permeability was irreversible increased, resulting in the release of UV-absorbing substances and ions. Besides, the decreased ability of Na+/K+-ATPase was also induced by combination effect. Our study indicated that the damaged cell membrane was the major factor of the mechanism of microbial inactivation by combination UHP with lysozyme or nisin, which lead to the leakage of cell contents and cell death, ultimately.The effect of UHP (100-500MPa) combined with6mg/mL lysozyme or200IU/mL nisin on Listeria monocytogenes in shrimp meat, as well as the qualities of shrimp meat were investigated. The result showed that it obtained4.0,4.6logCFU/g reduction of Listeria monocytogenes after300MPa combined with6mg/mL lysozyme and300MPa combined with200IU/mL nisin treatment, respectively, indicating that the two inactivation factors have a synergistic effect. Meanwhile, the mainly influence on the quality of shrimp meat was by pressure. The color of shrimp became white and yellow as the pressure increased. The hardness increased, and the springiness increased at low pressure region but decreased with the pressure higher. The pH slightly increased and the TVB-N value decreased, while the TBA value was not changed significantly at pressure range100-400MPa.The shelf life of UHP combined with lysozyme or nisin treated shrimp meat was studied.300MPa combined with6mg/mL lysozyme and 300MPa combined with200IU/mL nisin treated samples could achieved18and21days shelf life stored at4℃, respectively. Color and texture changes slowly during the whole storage compared with the control. And the total viable counts (TVC) were effectively inhibited during the storage time. At the same time, pH, TVB-N and TBA values increased slowly compared with the control during storage. So UHP combined with lysozyme or nisin can extend the shelf life of shrimp meat.