The Role of Rice Individual Kernel Moisture Content Distributions at Harvest on Milling Quality

Abstract

The objective of this study was to quantify the effects of rice kernel properties, associated with kernel moisture content (MC) distributions, on milling quality as harvest MC varied. Multiple samples of rice cultivars Bengal, Cypress, and Drew were harvested at various MCs from northeast and southeast Arkansas in 1999 and 2000. Additional sample sets of various rice cultivars were collected in 2004, 2005, and 2006 at various locations in Arkansas, Mississippi, and Missouri. Individual kernel MCs from panicles were measured immediately after each harvest. The percentages of kernels at MC levels >21%, >22%, >23%, >24%, >25%, and >26% and at MCs <12%, <13%, <14%, <15%, <16%, and <17% were quantified at various bulk harvest MCs. The percentages of kernels above various high MC levels increased with harvest MC. The percentages of kernels at different low MC levels and fissured kernels increased with a decrease in harvest MC, once the bulk harvest MC decreased below approximately 18%. Head rice yield reduction (HRYR) increased with increased percentages of both high and low MC kernels. Fissured kernels percentage had a good correlation with HRYR (R2 = 0.76). Head rice yield reduction in high MC kernels was postulated to be due to immature, high MC kernels; fissured kernels due to rapid moisture adsorption most likely caused HRYR in low MC kernels. Among low MC levels, the percentage of kernels at MCs less than 14% had the strongest correlation to HRYR (R2 = 0.72), whereas among high MC levels, the percentage of kernels at MCs greater than 22% correlated most strongly with HRYR (R2 = 0.61). Optimal harvest moisture contents (HMCs) were determined using quadratic equations derived from the percentages of kernels at MCs >22% and <14%. Based on this analysis, optimal HMCs ranged from 18% to 22% for long-grain cultivars, from 19.0% to 20.4% for medium-grain Bengal, and from 17.7% to 19.0% for long-grain hybrid XP723.