Effects of Rough Rice Moisture Content at Harvest on Peak Viscosity1

The effects of rice harvest moisture content (HMC) on pasting properties were investigated. One medium-grain and nine long-grain rice varieties were plot combine harvested at different intervals from three locations in 2002. Rough rice samples were dried and milled under controlled conditions, the head rice yield was recorded, and the rice flour was analyzed for pasting properties. The peak viscosity (PV) of rice flour within a given variety was generally inversely correlated with HMC. The rate of increase in PV as the HMC decreased depended on variety and location, which is speculated to be due to varying distributions of kernel moisture contents and resultant maturities. INTRODUCTION Rice kernel development, kernel size, and chemical composition change with maturation while kernel moisture content decreases progressively (Del Rosario et al., 1968). Therefore, kernel moisture content is an important indicator of rice kernel development. The studies of Del Rosario et al. (1968) and Kim et al. (2001) showed that when starch and protein synthesis are nearly completed, the rice kernel moisture content is approximately 30%; the composition of rice kernels harvested after this point reportedly does not change dramatically. Rice kernel-to-kernel development on panicles is non-uniform, which in turn produces a range of kernel moisture contents within a bulk at harvest. As such, physi1 This is a completed study.