Development of mathematical model for simulating moisture content during the re-wetting of brown rice stored in film packaging

In order to develop a re-wetting method for brown rice by using film packaging technique, a mathematical model suitable for designing the packaging was established. The re-wetting of brown rice was achieved by selecting a film permeability that controls the rate of water adsorption in the rice. In the model, changes in relative humidity (RH) inside the package were determined by incorporating the permeation rate of water vapour through the film and the rate of water vapour adsorption on the rice. The change in rice moisture content was determined from the mass of water vapour adsorbed onto the rice. For validation of the model, a 50 g of sample brown rice at a moisture content of 10% wet basis (w.b.) was packaged with a polybutylene terephthalate film pouch. The package was exposed to a humid environment of 25 °C and 89.5% RH for 10 weeks. The moisture content of brown rice in the package increased to 19% w.b. without cracking. Comparing measurements to values calculated from the proposed model, the model adequately described the changes in RH and the rice moisture content in the package with a root mean square error (RMSE) of 3.0% and a 0.2% dry basis (d.b.), respectively.