The Drying Of Tilapia Fillet Using Supercritical Carbon Dioxide

The main purpose of drying foods is to lower the moisture content in order to reduce water activity and prevent spoilage. Additionally, moisture removal reduces the weight and the bulk of food products to facilitate transport and storage. Traditional drying (e.g. air-drying) or modern drying (e.g. microwave-, freeze-, osmotic-and vacuum-drying) have advantages and disadvantages, but none is ideal in every respect. Though united drying could increase energy utilization, improve product quality, decrease drying time and reduce production cost, new, efficient and economic drying techniques also look forward to being used in the food industry.The supercritical CO₂ drying is a new drying technique, which is the combination of supercritical carbon dioxide extraction and drying. Drying techniques using supercritical CO₂ just begins in the utilization of food processing. In the paper, the supercritical CO₂ drying dynamics of tilapia fillet was studied, the process parameters of supercritical CO₂ drying were optimized by network platform of JMP 7.0, the mass transfer of supercritical CO₂ drying was simulated by matlab, and the quality of tilapia fillet were evaluated. The studied results were as follows:The supercritical CO₂ drying of tilapia fillet is feasible, the drying rate of which is better than that of vacuum-freezing drying and air-drying at a certain extent. Tilapia fillet heated before drying was in favor of supercritical CO₂ drying. Alcohol was added in supercritical CO₂, which could increase drying rate. Drying temperature had a significant effect on the process of supercritical CO₂ drying, while pressure and flow of CO₂ had a less effect on supercritical CO₂ drying. A mathematic model established on the supercritical CO₂ drying dynamics was as follows: MR=exp[-exp(0.0233T-1.7165)*t^0.7688]Experimental results showed that the model could be used to describe the supercritical CO₂ drying process of tilapia fillet. The artificial neural network model and the principle of selection on drying process parameters were established on the supercritical CO₂ drying of tilapia fillet based on the JMP7.0 software. The principle of selection on drying process parameters was as follows: if the dehydration rate of tilapia fillet must reach over 90%, the lowest temperature of supercritical CO₂ drying should be 46℃,the lowest pressure should be 13MPa, and the flow of CO₂ should be 10L/h 25L/h. The specific drying parameters should be choosed based on the principle and specific situation. It was illustrated that the temperature, pressure and flow of CO₂ had an effect on drying process. The higher was temperature and pressure, the better was drying effect. The influence of temperature on drying process was greater than that of pressure. The effect of flow of CO₂ on drying process was dependent on drying temperature. The effect of CO₂ flow on drying process was less in high temperature and larger in low temperature. A drying effect mode of supercritical CO₂ was put forward: the extraction drying effect was greater than hot drying effect in low temperature; both of the effects were equivalent at certain temperature; the hot drying effect was greater than extraction drying effect above the certain temperature.The mass transfer mathematical model of supercritical CO₂ drying was established on the base of differential mass conservation law. The relationship surface plots among the moisture content and drying time and drying room height were obtained by numerical simulation. The results indicated that the mass transfer of moisture was mainly convection-dispersion and axial diffusion was secondary in the supercritical CO₂ drying process.Compared with hot-air drying and vacuum freeze-drying, the supercritical CO₂ drying had significant advantages in sterilization. The appearance, colour, microstructure and texture of supercritical CO₂ drying products were equal to that of vacuum freeze-drying products, and were superior to that of hot-air drying products.