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ARS Home » Northeast Area » Wyndmoor, Pennsylvania » Eastern Regional Research Center » Food Safety and Intervention Technologies Research » Research » Publications at this Location » Publication #242904
Title: A combined treatment of UV-light and radio frequency electric field for the inactivation of Escherichia coli K-12 in apple juice

Author
item Ukuku, Dike
item Geveke, David

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/6/2010
Publication Date: 3/1/2010
Citation: Ukuku, D.O., Geveke, D.J. 2010. A combined treatment of UV-light and radio frequency electric field for the inactivation of Escherichia coli K-12 in apple juice. International Journal of Food Microbiology. 138:50-55.

Interpretive Summary: Radio frequency electric fields (RFEF) and UV-light treatments are individually used to kill bacteria in liquid foods. However, information on the efficacy of bacterial inactivation by combined treatments of RFEF and UV-light technologies is limited. In this study, we investigated the relationship between cell injury and inactivation of Escherichia coli K-12 in apple juice treated with a combination of RFEF and UV-light. Treated samples were analyzed for leakage of intracellular bacterial substances as a function of membrane damage and were plated (0.1 ml) on Sorbitol MacConky Agar (SMAC) and Trypticase Soy Agar (TSA) plates to determine population reduction of treated bacterial cells and percent injury among the surviving cells. UV-light treatment alone caused 6.5 log reduction of E. coli in apple juice while RFEF caused only 1.5 log reduction. A combination of the two processing treatments did not increase population reduction, cell injury or leakage of intracellular bacterial substances as compared to UV-light treatment alone. The results of this study suggest that RFEF treatment alone causes more injury to the bacterial cells than UV-light treatment. Also, the effect of the two processing treatment combination on bacterial inactivation was not synergistic.

Technical Abstract: Radio frequency electric fields (RFEF) and UV-light treatments have been reported to inactivate bacteria in liquid foods. However, information on the efficacy of bacterial inactivation by combined treatments of RFEF and UV-light technologies is limited. In this study, we investigated the relationship between cell injury and inactivation of Escherichia coli K-12 in apple juice treated with a combination of RFEF and UV-light. Apple juice purchased from a wholesale distributor was inoculated with Escherichia coli K-12 at 7.8 log CFU/ml, processed with a laboratory scale RFEF unit at 20 kHz, 15 kV/cm for 170 micro second at a flow rate of 540 ml/min followed by UV-light treatment at 25, 30 and 40 C. Treated samples were analyzed for leakage of UV absorbing substances as a function of membrane damage and were plated (0.1 ml) on Sorbitol MacConky Agar (SMAC) and Trypticase Soy Agar (TSA) plates to determine viability loss and percent injury. UV-light treatment alone caused 6.5 log reduction of E. coli in apple juice while RFEF caused only 1.5 log reduction. Percent injury caused by RFEF and UV-light processing alone averaged 95% and < 1%, respectively. A combination of the two processing treatments did not increase cell injury or leakage of UV-substances. Similarly, the viability loss determined was not significantly (P<0.05) different than RFEF or UV-light treatment alone. However, the UV-absorbing substances determined in apple juice treated with RFEF was significantly (P>0.05) different than UV-light treated samples. The results of this study suggest that RFEF treatment causes more injury to the bacterial cells leading to more cellular leakage of UV-substances than UV-light treatment. Also, the effect of the two processing treatment combination on bacterial inactivation was not synergistic.