Non-thermal effects of microwave and ohmic processing on microbial and enzyme inactivation: a critical review

•Controversial results in literature about non-thermal effects of electric fields.•Unreliable methods and assumptions can compromise results and conclusions.•Control and distribution of temperature and electric field are key factors.•Comparison with conventional process must be fair.•Depending on field frequency, effects may be subtle and difficult to assess. The use of microwave and ohmic heating in food processing has the advantage of a fast volumetric heating due to ionic and dielectric mechanisms, depending on field frequency. One topic that has been under debate is whether or not the electric field has a non-thermal effect that enhances the inactivation of microorganisms and enzymes. Numerous studies with controversial have been conducted using different approaches, experimental designs and methodologies. This review discusses important factors for accurately assessing non-thermal effects, such as distribution and control of electric field and temperature, measurement of time temperature history, sample homogeneity, fair comparison with conventional processed samples. Current theories for non-thermal inactivation of enzymes (structure and functionally changes) and micro-organisms (cell membrane changes) are also reviewed.