Effects of Different Drying Temperatures on Processing Quality and Physicochemical Properties of Rice

Abstract

The rice quality strongly depends on the paddy postharvest drying temperature. This study ascertains the optimal drying temperature for offering the best quality rice from a moist paddy. Moist paddy dried at different drying temperatures (40°C–80°C) was milled and studied for the possible alteration in rice quality, that is, kernel crack percent, head rice yield, embryo retention percent, nutrient content, gelatinization properties, rheological properties, and others. The study found that higher drying temperatures resulted in an increased kernel crack percent and decreased head rice yield, whitening percent, and embryo retention percent. At temperatures above 70°C, the structure of starch granules in polished rice became loose, with enlarged gaps between granules in the transverse section. The lowest fat (0.43%) and protein (8.08%) contents were observed at 80°C, while the highest starch content (74.10%) was also recorded at this temperature. Rice dried at 40°C showed superior gelatinization properties, with the highest peak viscosity (4430.00 cP), trough (2314.50 cP), and breakdown (2115.50 cP). In contrast, the apparent viscosity of rice dried at 70°C and 80°C was higher than that of rice dried at lower temperatures before the shear rate reached 10 s⁻¹. Additionally, the polished rice dried at 40°C had the highest total phenolic acid content (63.20 mg GAE/100 g) and scavenging capacities for ABTS (2,2 ^′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) (55.60%) and DPPH (2,2-diphenyl-1-picrylhydrazyl) radicals (63.23%). These findings suggest that drying temperatures below 50°C are optimal for preserving the nutritional quality of rice before milling. This study provides valuable insights for enhancing the nutritional value and overall quality of processed rice.