Inactivation of yeast and bacteria using combinations of radio frequency electric fields and ultraviolet light

Authors: Geveke, David

Submitted to: Journal of Food Processing and Preservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2020
Publication Date: N/A
Citation: N/A
DOI: https://doi.org/10.1111/jfpp.14385

Interpretive Summary: Pasteurizing juice nonthermally, without heat, maintains the utmost quality, but not all nonthermal processes work the same. Radio frequency electric fields (RFEF) is a nonthermal technology, developed by ARS, that has been shown more effective at killing yeasts than bacteria. On the other hand, ultraviolet light (UV), another nonthermal technology developed by ARS, has been demonstrated better at killing bacteria than yeasts. The present study is the first to combine RFEF and UV as a method to pasteurize bacteria and yeast. Apple juice was inoculated with Escherichia coli and Saccharomyces cerevisiae and nonthermally processed with RFEF, UV, or a combination of RFEF and UV. At 40 C, the combined process pasteurized both S. cerevisiae and E. coli, whereas the individual processes were unable to. The energy of the combined process, 49 J/ml, was nearly the same as that of the most efficient thermal process currently available. Combining the nonthermal RFEF and UV processes capitalizes on the strength of each individual process to pasteurize yeasts and bacteria and will result in safe and delicious juice.

Technical Abstract: Combining two nonthermal processes may intensify inactivation of microorganisms in juice. Radio frequency electric fields (RFEF) is a nonthermal technology that is more effective at inactivating yeasts than bacteria, while nonthermal ultraviolet light (UV) is the opposite. Apple juice was inoculated with Escherichia coli K-12 and Saccharomyces cerevisiae and processed with RFEF, UV, RFEF+UV or UV+RFEF at 40 and 50 C. RFEF conditions were 15 kV/cm and 170 microseconds treatment time. UV conditions were 254 nm and 12 s treatment time. At 40 C, RFEF inactivated 4.0 log S. cerevisiae and 1.5 log E. coli, while UV inactivated 0.8 log S. cerevisiae and 4.9 log E. coli. The combined processes inactivated 4.9 log S. cerevisiae and 5.8 log E. coli. Neither the order of the processes, nor temperature, significantly effected inactivation (P<0.05). The energy density of the combined process was 49 J/ml. These results will assist in efficient design of nonthermal pasteurization systems for liquid foods.