Factors affecting viscosity changes in corn

Abstract

Corn meals with known differences were tested using the Rapid Visco Analyzer. Various tests included the effect of solid concentration, effect of heating rate, effect of particle size, effect of Sodium Carboxymethylcellulose (CMC) and effect of heating rate, holding temperature and CMC. Differences were found to exist between meals from different crop years which were not attributable to particle size. When tested at 13, 15 and 17% solids, new meal consistently developed viscosity earliest. Aged meal consistently developed the least amount of viscosity. At 17% solids, a distinct peak was formed by new meal. When heated at various heating rate (2, 7 and 14'C/min), the slowest heating rate developed a distinct peak. New meal consistently developed viscosity earliest. Aged meal developed the least amount of viscosity. As particle size decreased, viscosity increased. The addition of various amounts of CMC showed significant differences in viscosity at 95'C. CMC changed the order of highest viscosity and masked differences in peak time. When testing heating rate, holding time and addition of CMC, 95'C was found to develop viscosity to a greater degree than 70'C. Holding temperature did not have a significant effect and CMC masked differences between samples and produced unusual curves. Whole and decorticated corns were stored for various lengths of time at 60, 50, 22 and 6'C. Density decreased over time when stored at elevated temperatures. Hardness values increased, indicating a softer grain. However, this is more likely an indicator of brittleness. Decorticated grains developed higher viscosity. Pericarp acts as a diluent. Peak temperature increased with storage at elevated temperature. Density, hardness, peak viscosity and peak temperature were found to be the most significant indicators measured.