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As an emerging electrotechnology, induced electric field has attracted extensive attention in the development of innovative heat treatment equipment. In this study, a resistance heating unit based on induced electric field was built for inner heating of aqueous electrolyte solutions as well as liquid foods, such as vinegar. NaCl solutions and liquid foods with different conductivity were used to investigate the thermal effect and temperature rise of samples. Saline gel composed of 3% agar powder and 20% NaCl acted as a coil of conductor for inducing high-level output voltage. The utilization of the saline gel coil significantly improved the power conversion efficiency of the heating unit as well as the heating rate. The results revealed that duty cycle and applied frequency had immediate impact on the efficiency of inner heating. Additionally, the rate of temperature rise was proportional to the conductivity of the sample. The temperature of 200 mL NaCl solution (0.6%) increased from 25 °C to 100 °C in 3 min at 40% duty cycle and 60 kHz of applied frequency, and it was a circulating-flow process. The maximum temperature rise of black vinegar was 39.6 °C in 15 s at 60 kHz and 60% duty cycle, while that of white vinegar was 32.2 °C in 30 s under same conditions, whereas it was a continuous-flow process. This novel heating system has realized the inner heating of liquid samples. [ABSTRACT FROM AUTHOR]

The novel, previous unreported induction heating technique developed here uses the inverse process of the existing induction heating techniques. The theoretical basis for developing this technique is to determine whether the induced current passing through a winding food coil would induce a magnetic flux or cause an increase in primary current. Therefore, to develop this technique and implement it in the food industry, it is necessary to understand its technical details and engineering characteristics. This study presents the design and development process of the technique, as well as the calculation formulas, including load voltage, induced electric field, induced current density, heating power and energy utilization rate during the heating process. The results reveal that although the application of this innovative inner heating technique has been achieved, the energy efficiency of the current system is low. The thermal effect and non-thermal effect of the induced electric field decreased the total bacterial counts in the samples of grapefruit juice and raw milk. Image 10083 • Innovative induction heating is a sister technology to ohmic heating in the food industry. • Liquid food can act as the secondary winding of a transformer for inner heating. • A thermal effect on liquid foods by an alternating magnetic field was observed. • The development and design process of this novel technique are presented. • Continuous-flow pasteurization of liquid food was achieved by an induced electric field. [ABSTRACT FROM AUTHOR]

Non-conventional heating technology based on electric fields can be utilized to process liquid foods. In this study, the induced electric field (IEF) was investigated to clarify its inactivation mechanism on E.coli. Staining results show that inactivation of E.coli by IEF can be attributed to the reversible destruction of the cell membrane, followed by the denaturation of intracellular enzymes, and finally the irreversible rupture of the cell membrane. The increased levels of extracellular proteins and nucleic acids were also observed. IEF treatment at 400 Hz and 800 V (or 53 V/cm) results in a reduction of 4.5 log CFU·mL−1 in the number of E.coli. Storage life analysis shows that IEF treatment can improve the stability of apple juice and the content of bioactive components. Thus, IEF is a potential technique for liquid food processing. • The inactivation mechanism of induced electric field on E.coli was investigated. • A reduction of 4.5 log CFU·mL−1 of E.coli was realized by applying the IEF. • IEF treatment retains bio-active components in fresh apple juice. • The storage stability of apple juice was improved through IEF treatment. [ABSTRACT FROM AUTHOR]