Differences in Kernel Shape, Size, and Density between Healthy Kernels and Mold Discolored Kernels and their Relationship to Reduction in Aflatoxin Levels in a Sample of Shelled Corn

Unacceptably high levels of aflatoxin in shelled corn drastically reduce its market value and result in substantial economic losses. This study looked at the reduction in aflatoxin levels that could be achieved by removal of kernels discolored by mold and presumed to contain aflatoxin. The study related kernel physical characteristics to the reduction achieved using screening and density separation techniques which are currently in use in the grain industry. Physical properties of corn kernels discolored by mold and healthy corn kernels were determined in a sample taken from a 737 kg corn lot known to have relatively high levels of aflatoxin. Properties measured included kernel diameters, sphericity, and kernel density. Differences between discolored and healthy kernels in major diameter, minor diameter, sphericity, and density were statistically significant. Tests were also conducted at a commercial inbred seed corn processing facility using a screen cleaner and a gravity table. Removal of fine material (approximately 10% by weight) reduced aflatoxin levels by 84%. In two successive passes through a screen cleaner, removal of smaller kernels and kernel pieces with a round-hole sieve further reduced aflatoxin levels by 1.8% and 9.4%, respectively. After the smaller kernels and kernel pieces were added back to the lot, two successive passes through a gravity table reduced aflatoxin levels by 12.6% and 16.4%, respectively. Kernel density distributions of a sample taken before gravity table density sorting, and of samples of the higher and lower density fractions after sorting, were also determined. The effect of screening with a slotted sieve was studied by screening a 3 kg sample from the corn lot using a table top Clipper cleaner. This 3 kg sample had been previously screened to remove fines. The results indicate that, at least for some corn lots, aflatoxin levels can be reduced using a screen cleaner and a gravity table. The authors also concluded that insight into the effectiveness of aflatoxin reduction in corn by size and density sorting could be gained by conducting a size and density analysis on a representative sample of kernels taken from the corn being sorted. Keywords: Aflatoxin, Corn, Density, Gravity table, Physical properties, Screening, Sieves.