Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: January 11, 2006
Publication Date: April 1, 2006
Citation: Geveke, D.J., Brunkhorst, C., Cooke, P.H., Fan, X. 2006. Nonthermal inactivation of e. coli in fruit juices using radio frequency electric fields . In: Juneja, V.K., Cherry, J.P., Tunick, M.H., editors. Advances in Microbial Food Safety. Washington, D.C.:American Chemical Society. p. 121-139. Technical Abstract: Radio frequency electric fields (RFEF) processing to inactivate bacteria in apple juice at moderately low temperatures has recently been developed. The process is similar to the pulsed electric fields process, except that the power supply is continuous rather than pulsed; therefore, the capital costs may be less. Orange juice and apple cider containing Escherichia coli K12 were exposed to electric field strengths of up to 25 kV/cm at frequencies ranging from 21 to 40 kHz. Following treatment at an outlet temperature of 65 C, the population of E. coli K12 in orange juice was reduced by 3.4 log relative to the control. Increasing the electric field strength and temperature and decreasing the frequency enhanced the inactivation. The electrical cost of the RFEF processing was approximately 0.0017 dollars per liter of orange juice. There was no change in brownness of orange juice nor was there any loss of ascorbic acid as a result of RFEF treatment. The population of E. coli K12 in apple cider was reduced by 4.8 log following RFEF processing at 60 C, whereas, thermal processing at the same time and temperature had no effect. Increasing the electric field strength and temperature enhanced the inactivation; however, there was no enhancement at lower frequency. Scanning electron microscope images of E. coli K12 that were thermally processed and RFEF processed indicated that the mechanisms of thermal and RFEF inactivation were dissimilar. The results of the present study provide the first evidence that the RFEF process inactivates bacteria in orange juice and apple cider containing solids at moderately low temperatures.