Study On Microwave Heating Characteristics Of Seasoned Freshwater Fish Fillet

The production of freshwater fisheries has been increasingyear-by-year in China. The freshwater fish resources can not be utilizedfully. To expand utilization of the freshwater fish resources, it isnecessary to develop high quality seasoned Fresh-water Fish Filletsproduction for microwave heating and improve the uniformity oftemperature distribution during microwave heating, systematicinvestigation of the microwave heating characteristic of seasonedfreshwater fish fillet product is necessary. The dielectric properties andsize of sample and the electromagnetic field intensity are the mostimportant influence factors of microwave heating characteristic.Thedielectric properties of three common species of freshwater fish (blackcarp, silver carp and spotted silver carp) at915MHz and2450MHz wereinvestigated, and then influence of salt solution soakage on dielectricproperties of black carp was investigated.The dielectric constants anddielectric loss rates were submitted to unsteady heat conduction equationand Maxwell’s equations with thermal properties to build atwo-dimensional mathematical model to predict and optimize thetemperature distribution of different size of fish fillet samples accordingto the finite element method (FEM).Through the above, following conclusions were obtained.Change in the dielectric properties of three species fish at twoselected frequencies are caused by difference in moisture content.Similar dielectric properties ranges to three species were observed,which may contribute to the similar main components of those samples.Due to moisture loss during heating caused by protein denaturation, thedielectric constant of the raw samples decreased more sharply withincreasing temperature than that of the preheated samples. Furthermore, moisture loss showed a greater effect on the dielectric constant than onthe loss factor. The complex dielectric properties of fish flesh wereestimated by applying Lichtenecker’s formula, and the effect of proteindenaturation on dielectric properties was investigated. It was shown thatonly moisture loss, which was caused by protein denaturation in fishflesh during heating, affected dielectric properties. Changes in proteinstructure during protein denaturation have no direct effect on dielectricproperties.Selected salt as the main consideration component for seasoningtreatment. Put black carp fillets in salt solution with differentconcentration(1%,2%,3%and4%) to prepare the socked samples. Theinfluences of temperature, frequency, concentration of salt solutions, andprotein thermal denaturation on dielectric properties were analyzed.Results showed that salt solutions soakage have more great influence ondielectric constant than that on dielectric loss factor. With increasingtemperature, the dielectric constant of the raw samples decreased moresharply than that of the preheated samples, and the dielectric loss factorof soaked raw samples increased more quickly than that of the preheatedsamples, which was due to moisture loss during heating caused byprotein thermal denaturation. The dielectric loss factor of samplesincreased with increasing of the salt concentration of solution. Thepenetration depth of samples decreased with increasing of the saltconcentration of solution.The temperature distribution and heating rate of hot-spot andgeometrical center of the cylindrical soaked black carp fillet sampleswere measured during microwave heating, where the diameter of thesamples were35.0mm, and the output power were300W,400W and500W respectively. Results showed that the output power has a significant impact on the temperature distribution in samples. Heating inlow power is more benefit to uniform temperature distribution andmicrobiological safety. The thermal properties(density, specific heat andthermal diffusivity) of soaked fish fillet samples at10℃~90℃werestudied to build a temperature distribution mathematical model. Densityof samples decreased with increasing temperature. Specific heatinccerased with decreasing temperature. The dielectric constants anddielectric loss rates were submitted to unsteady heat conduction equationand Maxwell’s equations with thermal properties to build atwo-dimensional mathematical model to predict and the temperaturedistribution of different size of fish fillet samples according to the finiteelement method by the software COMSOL3.5a. The comparison ofnumerical value and experimental value demonstrated that mathematicalmodel can predict the temperature distribution of samples well.The temperature distribution of different size of fish filletsamples could be predicted and optimized during the data analysisprocess. Provide a theoretical basis to the high quality freshwater fishfillet product in industrial production.