Microbial inactivation by ohmic heating: Literature review and influence of different process variables

Abstract

Background: The elimination of microbial cells is one of the most critical steps in food processing. Conventional heating is the application of diffusive and convective heat mechanisms and is traditionally applied to assure food safety. However, such process is also harmful to others thermosensitive compounds, compromising desirable sensorial characteristics. The large temperature gradients caused by conventional heating result in lower thermal efficiency, overheated zones and high processing times. To overcome these limitations, emergent technologies have been studied in the past years, such as ohmic heating. Scope and approach: The aim of this review was to analyse the state of the art of microbial inactivation by ohmic heating. This study emphasizes comparisons of ohmic and conventional heating, as well as comparisons of ohmic heating in several distinct scenarios (such as variations in the frequency and electric field). Key findings and conclusions:The literature analysis shows that the most analysed microbial species was Escherichia coli and studies dealing with fungi were less numerous comparing with studies dealing with bacteria. Concerning the lethality of conventional and ohmic heating, authors have shown that ohmic treated foods had smaller D values in various temperatures. The effect of frequency lacks of experimental data to explain the real impact of this parameter in the inactivation rate, once different authors have found divergent results. Moreover, increases in the electric field and salt content and decreases in the pH, fat and solid content have demonstrated higher heating rates and, therefore, higher inactivation rates.

Modeling the Inactivation of <i>Byssochlamys fulva</i> During Ohmic Heating of Lime Juice

“…[14] also demonstrated that the effect of temperature in combination with the effects of pH and voltage gradient can considerably enhance the effectiveness of ohmic heating on E. coli O157:H7 inactivation. According to Figure 2, by increasing the temperature, the main effect of pH on Byssochlamys fulva inactivation is significant [15]. also reported that at lower pH values, the effectiveness of orange juice pasteurization during both conventional and ohmic heating was more signified.…”

Ohmic Heating: A Review and Application in Food Industry

“…Previous invention use ohmic heating in the making of Frankfurt-type sandwiches by passing an electric current for a certain period of time. However, this method disappeared due to the lack of resources and technology [1]. In the last two decades, materials and designs for Ohmic heating have been improved.…”

“…Ohmic heating is a development of conventional heating. Conventional heating requires more time in which protein denaturation occurs and destroys nutrients in food [1]. In ohmic heating, the heat spreads evenly and quickly throughout the product due to the increasing of permeability cell wall, which this phenomenon will speed up the heating process with minimal damage to nutrition [2].…”

Design of Saline Gel Coil for Inner Heating of Electrolyte Solution and Liquid Foods under Induced Electric Field

“…Ohmic heating depends upon the conductivity of the sample and electric field strength; it is an inner heating process. According to Joule’s effect, the liquid medium to be processed acts as an electrical resistance (or the load) in the circuit; when the current passes through the interior of the sample, the electrical energy is thus converted into thermal energy [ 14 ]. However, it involves direct contact between the medium and active electrodes.…”