Inactivation Of CO₂-assisted High Pressure Processing On Escherichia Coli And Staphylococcus Aureus

The effects of CO2-assisted high pressure processing (HPP) on inactivation of dioxide Escherichia coli and Staphylococcus aureus was investigated in this study. The possible inactivation mechanism was proposed by analysis of cellular and molecule level, and finally we conduct the method of CO2-assisted HPP (CO2+HPP) in cucumber and apple juice processing. The researching contents were as followed.(1) Effects of gas-inflation methods, gases (CO2, N2, and N2O), inflated volume, phase stage, HPP conditions, and different system (PBS, cucumber juice, and apple juice) on inactivation of E. coli and S. aureus by CO2+HPP. Comparing with head-space inflation method, the vacumm inflation of 20% CO2 was shown to have significant assisted-inactivation effect with HPP; the resistance of E. coli and S. aureus at stationary phase was higher than those at mid-exponential phase; and the cucumber and apple juice showed higher protection effects on inactivation of E. coli and S. aureus compared with phosphate buffered saline (PBS); the maximum concentrate of CO2 dissolved in solution during HPP was 0.7 mmol;(2) Inactivation kinetics of CO2+HPP on E. coli and S. aureus. All inactivation curves showed lag tail and the Biphasic model has been chosen as the most suitable model. CO2 showed the highest assisted inactivation when combined with 200 MPa/3 min,300 MPa/3 min, and 400 MPa/3 min;(3) Effects of CO2+HPP on membrane permeability, morphology and interior structure of E. coli and S. aureus. CO2+HPP induced significant damage on cell membrane and severe damages in both morphology and interior structure of E. coli and S. aureus. After CO2+HPP, the membrane was wrinkled and twisted, and the permeability was increased, plenty of cytoplasm was outflow. The activity of enzymes in cells, leucine arylamidase and Naphthol-AS-BI-phosphohydrolase in E. coli and a-glucosidase in S. aureus was inactivated by CO2+HPP;(4) Proteomic method was used to analyze the possible mechanism of the inactivation of E. coli by CO2+HPP. Plenty of proteins were down regulated by HPP while less were induced by CO2+HPP. It was probably due to the reaction of acid stress, which was cause by CO2 before HPP, lead to plenty of proteins up regulated. And they will covered the down regulated proteins caused by CO2+HPP;(5) The probable inactivation mechanism of CO2+HPP is:1) on cellular level, CO2+HPP induced significant damage on cell membrane and severe damages in both morphology and interior structure; 2) on molecular lever, CO2+HPP down regulate proteins involved in physiological metabolism and assemble of cell membrane, and the synthesis of RNA and DNA had been disturbed, which caused lethal effect on cells;(6) 20% CO2+600 MPa/3 min treated cucumber and apple juice showed microbial safety during storage of 15 and 22 days at 4℃, respectively, and the growth curves of total plate count, yeast & molds and Lactobacilli flora present shape of "S" and fitted by Logistic model. During storage, the residue activity of pectin methylesterase (PME) and polyphenol oxidase (PPO) in apple juice were significantly decreased, and the activity of invertase of apple juice and the lipoxygenas (LOX) of cucumber juice were well retained, which are benefit in the stability, color, and flavor of the juice during storage. After the sensory evaluation, cucumber juice and apple juice treated by 20% CO2+600 MPa/3 showed good acceptability after storage for 7 days and 15 days at 4℃, respectively.