Ohmic Heating Study Of Conditioned Meat Product

Ohmic heating(OH),which is known as a technology based on Joule's law,with the mechanism of generating heat inside material via passing current through,has been studied for decades.Ohmic heating was considered to be promising with the advantages such as uniform heating,high energy transforming efficiency,and shorter heating time compared with traditional method.There have been studies on many kinds of food material,but few on hamburger patty,which is one kind of minced meat products and has been popular among fast food industry and house-cooking.This research focused on the OH of hamburger patty at both high and low frequency(20 kHz and 50 Hz),and analyzed the electrical properties,temperature distribution of sample after being heated from 10 ? to 80 ?.Simulation work was carried out to establish model of sample after heating,and to reveal the temperature distribution tendency.This research was aimed at the feasibility of applying ohmic heating method on hamburger processing.1.The samples were heated by alternative current of 20 V at 20 kHz and 50 Hz to measure the electrical conductivities.When the samples were heated from 10 to 80 ?,the electrical properties of samples were measure with an LCR meter at 12 frequency points,then the EC of samples were calculated according to the measured resistance(R)value.The ECs of samples heated by 20 kHz varied from 0.7 S/m to 3.54 S/m from 10 ? to 80 ?,while the ECs of sample heated by 50 Hz varied from 0.93 S/m to 3.78 S/m in the same temperature range.With temperature rising,the EC of sample increased.Also,the EC showed frequency tendency that when frequency increased,the EC of sample became larger,especially under 5000 Hz,the increasing rate of EC was higher.2.Due to the invisibility of close heating system,software COMSOL Multiphysics was applied to simulate the OH under 20 V at both 20 kHz and 50 Hz of hamburger patties,in order to obtain the temperature change and distribution inside samples during heating.In the simulation work,as there were less energy loss and higher energy transforming efficiency,compared with the experimental operations,the heating time for sample to reach target temperature was shorter for both heating frequencies(80 s for 20 kHz and 204 s for 50 Hz),and then lead to more uniform temperature distribution inside the samples.3.Temperature history was taken when the samples were heated by alternative current of 20 V at 20 kHz and 50 Hz.The heating time for the center of sample to reach target temperature 80 ? was 131.11 s and 290.5 s at 20 kHz and 50 Hz,respectively,which revealed that higher frequency could shorten the heating time.Comparing the drip loss under two frequencies,20 kHz could reduce the drip loss so that higher quality of food product could be assured.Thermal pictures taken by infrared camera showed the temperature distribution of samples after heating.The tendency of temperature distribution was same as simulated results that the highest temperature occurred at the center of the sample while the lowest occurred at the edge of the sample.It proved the accuracy of simulated results.When applying 50 Hz heating,the corrosion of electrodes happened,which led to the contamination of sample by ions.The corrosion problem is one of the important factors which should be taken into consideration when designing low frequency ohmic heating system.According to the experimental and simulation work,the feasibility of applying OH on hamburger processing was proved,and the advantages such as short heating time and uniform heating of OH were confirmed.