The effect of drying temperature on the physical and antioxidant qualities of MARDI Warna 98 rice

Abstract

Drying is an important activity after the rice is harvested in order to minimize quality deterioration. Generally, drying temperature ranging from 42-45°C is known worldwide to preserve rice physical quality, mainly for white rice and it is widely practised by all rice millers. A study was conducted to determine the optimum drying temperature of the new coloured rice variety, MARDI Warna 98 (MW 98) in the preservation of physical as well as antioxidant qualities. The rice was dried at ambient temperature as control and ovendried at 40-45°C, 46-50°C and 51-55°C until moisture content reached 13-14%. Physical qualities that have been determined were head rice and broken rice, while the antioxidant properties evaluation measured were total phenolic content (TPC), total flavonoid content (TFC), total anthocyanin content (TAC) and 2, 2-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activities. Antioxidant parameters were measured spectrophotometrically. The results showed that the head rice recovery was significantly lower at ambient temperature and 51-55°C drying temperature (90.59% and 91.23%, respectively) and this was directly proportional to a higher percentage of broken rice (9.41% and 8.77%, respectively). The results also showed no significant difference in head rice recovery either drying at 40-45° or 46-50°C, which were 95.50% and 95.93%, respectively. The rice was then evaluated for its antioxidant activities and results showed there was no significant difference in the content of total phenolic, total flavonoid, total anthocyanins and DPPH radical scavenging activities at different drying temperatures except for ambient temperature. Rice dried at ambient temperature showed significantly lower content of total phenolic, total flavonoid, total anthocyanins and DPPH inhibition. In conclusion, drying temperature does affect the physical and antioxidant qualities of MW 98. Therefore, we suggested that drying at 46-50°C was the best for MW98 to preserve rice’s physical and antioxidant qualities.