Inactivation of in Apple Juice by Radio Frequency Electric Fields

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 processing has recently been shown to inactivate yeast in water at near-ambient temperatures. The objective of this study was to extend the radio frequency electric fields (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 colony-forming units (CFU)/mL. Applying 3 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 1st evidence that RFEF processing inactivates bacteria in fruit juice at moderately low temperatures.

Radio frequency electric fields processing of orange juice

“…Typically in RFEF and PEF processing, inactivation is dependent on field strength (Barsotti & Cheftel, 1999;Geveke & Brunkhorst, 2003, 2004b. However, a similar result to that observed in this study was reported for RFEF processing of apple juice (Geveke & Brunkhorst, 2004a). Inactivation increased as the electric field strength increased up to 16 kV/ cm.…”

“…RFEF processing at 30 kV/cm and 20 kHz reduced the population of Saccharomyces cerevisiae in water by 3.8 log (99.98%) at 35°C (Geveke & Brunkhorst, 2003). RFEF processing at 21 kV/cm and 55°C inactivated Escherichia coli K12 in apple juice by 1.9 log (98.7%) relative to the control (Geveke & Brunkhorst, 2004a). Raising the temperature increased inactivation.…”

“…The chambers were made of Rexolite, a transparent cross-linked polystyrene copolymer (C-Lec Plastics, Philadelphia, PA). The treatment chambers were designed to converge the orange juice into a narrow flow area in order to reduce the power requirement (Geveke & Brunkhorst, 2004a;Matsumoto, Satake, Shioji, & Fig. 1.…”

Radio frequency heating of comminuted meats - considerations in relation to microbial challenge studies

“…Therefore, factors present in the current study, that were not present in the study by Byrne et al (2006) may have attributed to the higher reduction of spores. These factors could include [1] the RF energy having a non-thermal effect on the inactivation of the spores (Geveke & Brunkhorst, 2003;Kozempel, Annous, Cook, Scullen, & Whiting, 1998;Ponne, Balk, Hancioglu, & Gorris, 1996;Geveke & Brunkhorst 2004); [2] the longer heating up times during RF cooking of PLM in the current study compared to those in Byrne et al (2006) may have thermally damaged the spores thereby giving an underestimate of the actual numbers present. However, a separate dedicated study would be required to determine the actual cause of these differences.…”

Electromagnetic Solutions for the Agricultural Problems

“…Although attraction is also reported, a reapetable test has not been verified. However, nonethermal effects of electromangetic waves on living tissue has been confirmed (Geveke & Brunkhorst, 2006). The imaginary part of the dielectric constant can be used to heat up a material remotely using radio waves.…”