Kale Juice Quality During Ohmic Heating and Induced Electric Field Treatment: Comparison in Terms of Ion Currents and Induced Magnetic Fields

Both ohmic heating (OH) and induced electric field (IEF), as representative electrotechnologies, are typically evaluated independently. Therefore, comparative evaluation under similar conditions was necessary using kale juice to elucidate their processing characteristics and to determine whether ion currents in conductive food matrices generate detectable induced magnetic fields. Under identical electric field strengths (18.08 or 26.92 V/cm) and target temperatures (60 or 70 °C), ion currents (118.6–162.0 mA) and induced magnetic fields (0.0079–0.0108 mT) were simultaneously quantified using an integrated oscilloscope-Hall sensor system, confirming detectable electromagnetic responses associated with ion currents in the juice. Both electrotechnologies achieved > 7 log₁₀ CFU/mL reductions of Escherichia coli and Leuconostoc pseudomesenteroides at 70 °C, whereas conventional heating (CH) retained 0.90–1.33 log₁₀ CFU/mL survivors. Mechanistic analyses showed that IEF and OH induced significantly greater intracellular component leakage than CH, supporting the involvement of electroporation in microbial inactivation. Moreover, in fresh kale juice, IEF-60 preserved green color (a* = −2.41; and ΔE = 2.36) and chlorophyll content (92 μg/mL) more effectively, compared to OH-70 and CH-70 while maintaining comparable or higher microbial reduction. These findings provide direct evidence of detectable induced magnetic fields in food matrices and clarify the functional differences between direct and indirect electric field modes, supporting IEF as a promising non-contact technology for balancing microbial safety and quality retention in complex cloudy juices.