Effects of infrared radiation drying and heat pump drying combined with tempering on the quality of long‐grain paddy rice

Abstract

AbstractThe objectives of this study were to study the effects of two drying methods, infrared radiation (IR) drying and heat pump (HP) drying, combined with tempering in the glassy state on the quality of long‐grain paddies (O. sativa L. subsp. indica) and the effects of intermittent ratios (δ = 0, 1, 2, 3, 4) on the milling properties and texture profiles of the paddies. The tempering temperature was set at 60 °C, according to the glass transition temperature (Tg) of the paddy rice, which was determined to be 58 ± 2 °C using low‐field nuclear magnetic resonance (LF‐NMR) technology. The results showed that, compared with HP drying, IR drying resulted in a higher drying rate and was more effective, but the rate of moisture reduction was more uniform under HP drying. The tempering process had positive effects on the milling and texture profile analysis (TPA) properties of the paddy rice. Overall, intermittent ratios of δ = 3 and δ = 2 are recommended for HP drying and IR drying, respectively. However, no significant differences in the effects of different drying methods and intermittent ratios on water diffusion in the paddy rice were found through MRI analysis.