Modeling Equilibrium Moisture Content of Brown Rice as Affected by High-Pressure Processing

Abstract

Moisture sorption isotherms (MSI) of presoaked brown rice after high-pressure (HP) treatment (100 to 500 MPa for 10 min at ~20°C) were evaluated at 20°C to 40°C, and five existing models were tested for prediction performance. Equilibrium moisture content (EMC) of HP-treated samples at various relative humidities showed a concave upward trend, with the 300 MPa treated samples yielding the lowest EMC value. Hysteresis was observed with all treated samples. All MSI models performed well, and the modified Guggenheim-Anderson-de Boer (GAB) model gave the best fit. The mobility and distribution of water in equilibrated brown rice were studied by nuclear magnetic resonance (NMR) analysis. The proton distributions of the samples revealed three or four distinct water populations, which varied with equilibrium relative humidity (water activity). HP treatment resulted in a change in the water distribution and caused the water to be less mobile. Scanning electron microscopy (SEM) confirmed that HP treatment resulted in alteration of the surface structure of the starch granules. This study helped to develop a modified MSI model and better understanding of the water distribution in brown rice treated with HP.