Antimicrobial Effect of Combination Treatment with High Pressure Processing and Mild Heat Against Foodborne Pathogens in Apple Puree

The objective of this study was to determine the antimicrobial effect of the combination treatment of high pressure processing (HPP) and mild heat against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes in apple puree. Also, we determined the levels of sub-lethally injured cells according to the treatment condition. Inoculated apple puree was treated at 300 or 400 MPa for up to 7 min at 20, 35, or 50 °C. Increasing the pressure level or treatment temperature resulted in larger reductions of foodborne pathogens. Moreover, the antimicrobial effect of the combination treatment was prominent in apple puree at pH 3.5 than pH 3.8. E. coli O157:H7 and L. monocytogenes exhibited more resistance to the combination treatment with HPP and mild heat than S. Typhimurium. Also, a high proportion of sub-lethally injured E. coli O157:H7 cells was observed. No significant differences in pH, soluble solid contents, and the color of apple puree between control and HPP and mild heat-treated samples were observed during storage for 28 d at 5 °C. This study provides insights into predicting the inactivation patterns of pathogenic bacteria in apple puree by the combination treatment with HPP and mild heat for practical applications.