Effects of Processing Conditions and Environmental Exposure on the Tensile Properties of Parboiled Rice

Ultimate tensile strength (UTS) and tensile modulus of elasticity (MOE) of parboiled rice were investigated. UTS and tensile modulus were measured for two rice varieties, Lemont and Rico-1, with respect to 5 and 10 min steaming durations, 21 and 40 °C drying temperatures, four storage environments of no exposure, 65, 86 and 100% relative humidity (RH) at room temperature, and six exposure durations of 0, 1, 2, 3, 9 and 24 h. Long grain, high amylose Lemont was found superior in UTS and MOE than medium grain, low amylose Rico-1, both before and after parboiling. Increasing steaming duration from 5 to 10 min increased the degree of parboiling, and consequently increased the UTS and MOE in both the varieties. Increasing drying temperature from 21 to 40 °C decreased the strength properties. Effect of storage environment and RH on the tensile strength properties revealed that in no exposure condition as well as 65% RH environment the tensile strength properties increased slightly or remained stable. When exposed to higher than 65% RH environment at room temperature the strength properties progressively decreased over storage period. The decrement rate was fast with high humidity of 100% and prolonged storage of 9–24 h, and the decrease was as high as 66·6% of the initial strength.