Synergistic Antibacterial Effect Of Petit-high Pressure CO₂ Combined With Cinnamon Essential Oil And Its Application In Milk Pasteurization

Petit-high pressure CO₂（petit-high pressure carbon dioxide,p-HPCD）is a nonthermal pasteurization technology,which has many advantages such as low price,easy to obtain,and no residue.However,due to its applied CO₂ pressure,long treatment time or high process temperature are usually necessary to ensure microbial safety.Therefore,the construction of p-HPCD-based combined pasteurization technology is of great significance to promote its practical application in food processing.Plant essential oils are natural antimicrobials.However,high dose of plant essential oils has unpleasant odor and could have adverse effects on intestinal cells.This paper studied the synergistic antibacterial interaction of common foodborne pathogens Salmonella typhimurium and Listeria monocytogenes between p-HPCD and CEO,and the synergistic mechanism of p-HPCD and CEO against S.typhimurium.Finally,the application of p-HPCD combined with CEO in pasteurization and preservation of milk was also carried out.The main results are as follows:（1）Synergistic antibacterial interaction of p-HPCD and plant essential oils（EOs）against S.typhimurium and L.monocytogenes.Cinnamon EO（CEO）exhibits better inhibitory effects on S.typhimurium and L.monocytogenes.Compared with p-HPCD or CEO treatment alone,the inactivation effect of p-HPCD combined with CEO on two pathogens was significantly increased.At 1.3 MPa and 30℃,the survivals of S.typhimurium and L.monocytogenes were decreased by 5.39 and 5.49 log₁₀ CFU/m L,respectively,after p-HPCD+CEO（final concentration was 0.03125%）treatment for 3 h,significantly higher than p-HPCD or CEO alone（p<0.05）.It was found that combined treatment showed synergetic effect on S.typhimurium and L.monocytogenes inactivation,and the effect against S.typhimurium was stronger than L.monocytogenes.（2）Synergistic antibacterial mechanism of p-HPCD and CEO against S.typhimurium.After p-HPCD（1.3 MPa）combined with CEO（final concentration was 0.03125%）treatment at 30℃for 3 h,obvious cell morphological changes of S.typhimurium were observed.Cell membrane permeability was increased and membrane potential was decreased,resulting in the destruction of cell membrane integrity and the leakage of intracellular proteins,ATP and other substances.Moreover,combined treatment caused the increase of intracellular ROS,which could disturb the intracellular redox homeostasis,thereby induce cell oxidative damage.The above severe cell changes could be the main synergistic antibacterial mechanism of p-HPCD and CEO.In addition,p-HPCD combined with CEO can inhibit the expression of virulence genes such as fil C,hila,invl and ssr A,which may reduce the pathogenicity of S.typhimurium.（3）Application of p-HPCD combined with CEO in milk pasteurization.After being treated by p-HPCD（1.3 MPa）combined with CEO（final concentration was 0.03125%）at 40℃for 6 h,the survivals reduction of S.typhimurium in low-fat milk and whole milk was 3.18and 0.78 log₁₀ CFU/m L,respectively,and that of L.monocytogenes was 1.51 and 0.35 log₁₀CFU/m L,respectively,significantly higher than that after each individual treatment（p<0.05）.The combined treatment showed better antimicrobial effect on low-fat milk,and S.typhimurium in milk was more sensitive to the combined treatment.After 6-d storage at 4℃,compared with the untreated group,p-HPCD combined with CEO treated S.typhimurium in low-fat milk and whole milk was decreased by 4.67 and 1.41 log₁₀ CFU/m L,respectively,significantly higher than each individual treatment group（p<0.05）.However,combined treated L.monocytogenes in whole milk was not significantly inhibited relative to CEO alone treatment.The results also showed that p-HPCD and CEO in combination had good synergistic effects on S.typhimurium inactivation,but only L.monocytogenes in low-fat milk was synergistically inhibited by the combined treatment.