Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2003
Publication Date: 5/1/2004
Citation: Geveke, D.J., Brunkhorst, C. 2004. Inactivation of escherichia coli in apple juice by radio frequency electric fields. Journal of Food Science. 69(3):134-138.
Interpretive Summary: Radio Frequency Electric Fields (RFEF) processing is a promising new nonthermal alternative to heat pasteurization, but it has been limited in its application to very low conductivity liquids. A novel treatment chamber was developed that extends RFEF processing to the inactivation of bacteria in apple juice. Escherichia coli K12 was reduced by 1.8 log (or 98%) following exposure to an 18 kV/cm electric field at a temperature of 50 C for 4 sec. The results of the present study provide the first evidence that RFEF processing inactivates bacteria in fruit juice at moderately low temperatures.
Technical Abstract: Heat pasteurization may detrimentally affect the quality of fruit and vegetable juices; hence, nonthermal pasteurization methods are actively being developed. Radio frequency electric fields (RFEF) processing has recently been shown to inactivate yeast in water at near ambient temperatures. The objective of this study was to extend the RFEF technique to inactivate bacteria in apple juice. A converged-field treatment chamber was developed that enabled high intensity RFEF to be applied to apple juice using a 4 kW power supply. Finite element analyses indicated that uniform fields were generated in the treatment chamber. Escherichia coli K12 in apple juice was exposed for 0.17 ms to electric field strengths of up to 26 kV/cm peak over a frequency range of 15 to 70 kHz. The population of E. coli was reduced by 1.8 log following exposure to an 18 kV/cm field at an outlet temperature of 50 C. Raising the temperature increased inactivation. Intensifying the electric field up to 16 kV/cm increased inactivation; however, above this intensity, inactivation remained constant. Radio frequencies of 15 and 20 kHz inactivated E. coli better than frequencies of 30 to 70 kHz. Inactivation was independent of the initial microbial concentration between 4.3 and 6.2 log cfu/ml. Applying three treatment stages at 50 C increased inactivation to 3 log. The electric energy for the RFEF process was 300 J/ml. The results of the present study provide the first evidence that RFEF processing inactivates bacteria in fruit juice at moderately low temperatures.