Prediction of drying rate during frozen storage of cooked rice utilizing novel method of measuring adsorption isotherm.

Drying of foods generally triggers several quality deteriorations during long term frozen storage. It is thought to be due to the difference between ambient water-vapour concentration and water activity of food surface. Water activity is strongly related with water content and their relationship is expressed as adsorption isotherm. Several methods are proposed to measure adsorption isotherm. However, at low temperature about -18°C, measurement is difficult because usual methods can’t apply. In this study, in order to solve this problem, the novel easier method to measure adsorption isotherm was developed under the cold temperature circumstance. This method was developed by modifying Conway micro diffusion method that used silica gels as standard substance. Utilizing this method, adsorption isotherm of cooked rice was measured. Then predicting equation of drying rate was confirmed to be applicable by experimental verification. Finally, drying rate of cooked rice during constant low temperature storage was predicted by measured adsorption isotherm and predicting equation. The Prediction was presented almost the same trend with the experimental data.