Update on the Impact of Dry Extruding Cottonseed to Reduce Aflatoxin and Gossypol Levels

Cottonseed is an economical source of protein and is commonly used in balancing livestock rations; however, its use is typically limited by protein level, fat content, gossypol, and the potential for aflatoxin. Cottonseed and mixtures of cottonseed and cotton gin by-products (CGBP) were extruded at relatively high temperatures to determine if the process would reduce the free-gossypol and aflatoxin levels in the material, without degrading the nutritional value of the original material. Various mixtures of cottonseed and CGBP were used in the gossypol test to confirm previous tests conducted at the U. S. Cotton Ginning Laboratory in Stoneville, Mississippi. The results from this test indicated a 71 to 78% reduction in free gossypol levels for the various mixing ratios, based of the official AOCS standard methods. This reduction is most likely under estimated, since the official methods for determining free-gossypol levels are not specific to gossypol and constituents from other feed ingredients can interfere with the spectrophotometric determination. Cottonseed with aflatoxin levels in excess of 650 ppb was used to determine the effect of extrusion temperature and increased processing on the aflatoxin and nutritional values of the contaminated cottonseed. The variability of aflatoxin in contaminated lots is extremely high and although these tests used relatively small lot sizes, numerous samples, and rigorous sample collection techniques, the variability associated with the analyses was a major issue. The largest amount of variation was encountered in the nonextruded material and after the material was extruded, the variability was greatly reduced. Aflatoxin levels decreased on the order of 32 to 45% (based on mean values) as the extrusion temperature was increased from 104 C to 160 C (220 to 320 F). Most nutritional values were not significantly altered by the extrusion temperatures used in this test. Soluble protein was the exception; it was significantly decreased at the higher temperatures. Results from the test on multiple pass extrusion, indicated a decrease in aflatoxin levels and variability as the amount of processing increased on the order of 46 to 66% (based on mean values for four stages of processing compared to one stage of processing). Nutritional values associated with this test were not significantly altered by increased processing. Results from this study indicate that dry-extruding cottonseed to reduce gossypol and aflatoxin levels is an area of research, which should be further explored.