Influence of harvest moisture content and milling duration on microwave‐dried rice physicochemical properties

Abstract

Background and Objectives Harvest moisture content (HMC) and milling duration are important factors that influence milled rice quality. The goal of this study is to determine the effect of HMC and milling duration on the physicochemical properties of long grain and medium grain microwave‐dried rice. A long‐grain hybrid rice cultivar (XL753) and a medium‐grain rice cultivar (Titan) with initial HMCs of 16%, 18%, and 20% (wet basis) were sourced from rice farms in Arkansas, USA. The rice samples were dried with the 915 MHz industrial microwave at a specific energy of 525 kJ/[kg‐grain]. The control samples were dried with natural air in an equilibrium moisture content chamber set at 25°C and 56% relative humidity. Following drying, the samples were milled at milling durations of 30, 45, and 60 s, and physicochemical properties were determined. Findings HMC had significant (p < .05) impacts on head rice yield, crude protein content, and final viscosity of microwave‐dried rice for both cultivars. There were strong positive correlations (Titan: 0.86, XL753: 0.88) between HMC and head rice yield and negative correlations (Titan: −0.85, XL753: −0.62) between HMC and final viscosity of microwave‐dried rice. Milling duration significantly influenced the surface lipid content and whiteness index of microwave‐dried rice for both cultivars. Furthermore, milling duration had significant impacts on the starch damage content and trough viscosity of microwave‐dried rice cultivar XL753 but no significant impact on cultivar Titan. Statistical models predicted HMC of 20% and milling duration of 45 and 42 s for processing microwave‐dried rice cultivars Titan and XL753 respectively, to obtain rice with superior characteristics. Conclusions HMC and milling duration significantly influenced some physicochemical properties of microwave‐dried rice. We recommend that further studies should be conducted on the cooking, sensory, and storage properties of microwave‐dried rice, to provide information on end‐use and consumer acceptability. Significance and Novelty This study provides science‐based information that is vital for optimizing the harvesting and processing conditions of rice dried using the 915 MHz industrial microwave.