Effect of pH for inactivation of Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes in orange juice by ohmic heating

- This is the first study of the combined effect of pH and ohmic heating on inactivation of foodborne pathogens in orange juice.
- We confirmed that ohmic heating can effectively inactivate foodborne pathogens when combined with higher acidity.
- There were no significant changes in color and pH when the ohmic heating achieves maximal reduction in pathogen.

We investigated the combination effect of ohmic heating and pH for inactivation of Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes in orange juice. Juice of varying pH (2.5, 3.5, and 4.5) was inoculated with the pathogens and subjected to ohmic heating at different temperatures (50, 55, and 60 °C) for different times (from 0 to 60 s). The reduction of pathogens was higher as treatment temperature and time increased and juice pH decreased. At pH 2.5, populations of E. coli O157:H7 were reduced by > 1.81 log, to below the detection limit within 60, 30, and 20 s at 50, 55, and 60 °C, respectively. S. Typhimurium was reduced by 5.15 log within 60 s at 50 °C and to below the detection limit within 10 s at 55 and 60 °C. L. monocytogenes was little affected at 50 °C but was reduced by 2.15 and 3.37 log after 60 s treatment at 55 and 60 °C. There was a similar pattern of inactivation of the pathogens at pH 3.5 and 4.5. There were no significant quality changes after treatment. In conclusion, our results indicate that ohmic heating can effectively inactivate the pathogens and antimicrobial effect significantly increases when combined with higher acidity.