Effect of Electron Beam Irradiation on Gossypol, Chemical Composition and Fatty Acids of Whole Cottonseed

Whole cottonseed (WCS) is a byproduct of the cotton-fiber industry. It is readily available source of energy, protein and other nutrients for high producing dairy cows and other animals. The use of WCS in poultry diet is limited due to the presence of gossypol, cyclopropenoid fatty acids, high fibre and poor protein quality. Electron beam (EB) irradiation has been proved to be successful in decontamination, disinfestation and improvement of the overall quality of food and agricultural commodities. Recently, EB-irradiation was effective in reducing anti-nutritional factors. This study was completed to determine effects of EB- irradiation at doses of 10, 20, 30 and 40 kGy on gossypol, chemical composition and fatty acids of whole cotton seed.
WCS was packed in twelve 1520 cm2 polyethylene bags. The bags were exposed to various doses (10, 20, 30 and 40 kGy; three bags each per dose step) of EB- radiation with a fixed beam energy of 10 MeV using a Rhodotron accelerator. Feed samples were analyzed for crude protein (CP), ether extract (EE), crude fiber (CF) and ash as described by AOAC. Gossypol was determined according to ISO assay. Fatty acid composition was determined by gas chromatography with flame ionization detection (GC-FID) using a HP-6890 GC instrument. Data were analyzed as a completely randomized design according to the general linear models (GLM) procedure of SAS. The Duncan test was used to separate the means at the significance level of 0.05.
Free and total gossypol content of WCS were decreased by EB-irradiation in a dose-dependent manner. Major detrimental effects of gossypol on animals are labored breathing, dyspnea, decreased growth rate, anorexia and reduced fertility. Therefore, EB-irradiated WCS may be used in animal rations at higher levels without occurring gossypol toxicity. References dealing with mechanism of gossypol decomposition due to irradiation were not found in the literature. Generally, in the literature four types of radiation effects on biomolecules are reported: fragmentation, cross-linking, aggregation and oxidation by oxygen radicals that are generated in the radiolysis of water. Formation of bonds between gossypol and gossypol (aggregation) or between gossypol and other molecules (cross-linking) and fragmentation or breakdown of gossypol may occur by EB-irradiation. Chemical composition of WCS except crude fiber was not affected by radiation processing. EB-irradiation at 40 kGy decreased crude fiber content of WCS. The reduction in crude fiber by EB-irradiation may be due to oxidation of the cellulose, and conversion of cellulose and lignin to the cell wall solution. The decrease in crude fiber may improve WCS utilization by animals. EB-irradiation had a substantial effect on the linoleic acid present in WCS.
The present study revealed that EB-irradiation had the potential to reduce the gossypol and crude fiber and had a positive effect on the linoleic acid of WCS. It can be concluded that irradiation may be beneficial for improvement nutritional value of WCS as a feed source of animals.