Equilibrium Moisture Contents of Pureline, Hybrid, and Parboiled Rice Kernel Fractions

Abstract

The effects of temperature and relative humidity on the equilibrium moisture contents of rough rice, brown rice, and head rice from non-parboiled pureline cultivars Wells (long-grain) and Jupiter (medium-grain), hybrid cultivar CL XL730 (long-grain), and a parboiled rice (long-grain) of unknown cultivar, were investigated. In addition, equilibrium moisture contents of broken kernels, rice bran, and rice hulls of Wells cultivar were also investigated. Air conditions were maintained at temperatures of 10C to 60C, and relative humidities of 10% to 70% to measure kernel-fraction moisture contents. For each air condition, rough rice and constituent fractions were allowed to equilibrate, after which the equilibrium moisture content of each fraction was measured. Rice hulls attained the lowest equilibrium moisture content followed by rice bran, brown rice, broken kernels, and head rice; this held for both parboiled and non-parboiled samples. Five, three-parameter equations, namely, the Modified Henderson, Modified Chung-Pfost, Modified Halsey, Modified Oswin, and Modified Guggenheim-Anderson-DeBoer were evaluated for their ability to describe the sorption data of each kernel fraction. The Modified Chung-Pfost and Modified Guggenheim-Anderson-DeBoer equations were the most suitable for describing equilibrium data of rough rice, brown rice, broken kernels, and head rice of both parboiled and non-parboiled samples, followed by the Modified Oswin and Modified Henderson equations. The Modified Oswin equation was the most suitable for rice bran and hulls. The measured equilibrium moisture content of rough rice was closely predicted by the weighted average equilibrium moisture content of the kernel fractions.