154 Characterization of size and moisture content distributions of milled rice.

A. G. CNOSSEN, T. J. Siebenmorgen, and J. D. Reid. Dept. of Food Science, University of Arkansas, 272 Young Ave., Fayetteville, AR 72704.

Rice breakage during drying and subsequent milling is one of the major concerns of the US rice industry. A complete understanding of rice fissuring, and subsequent breakage, not only involves determining the causes of fissuring, but also the characterization of the physical properties, such as size and moisture content (MC) distributions, of the kernel itself. Characterization of distribution changes of these properties, as head rice yield (HRY) decreases with prolonged drying duration, could help more fully understand which kernels break during drying and milling. The objective of this study was to determine, from a kernel size and MC distribution perspective, which kernels break during drying, tempering, and milling of rice. Subsequently, fissure occurrence was correlated to kernel size. Rice from the 1998 harvest season, harvested over a range of MCs, was dried under various conditions and tempered for different durations. The different treatments resulted in varying HRY levels. Size distributions (length, width, thickness, and circumference) and individual kernel MC distributions of milled rice samples were measured for each HRY level. The number of fissured kernels in 100-kernel samples was counted for four size fractions to relate fissure occurrence to kernel size. Results indicate that the shorter and thicker kernels are the most prone to fissure formation and subsequent breakage during milling.