Gossypol removal from cottonseed

During the cottonseed oil processing when the oil is removed from the cottonseed, some gossypol will also be extracted and remain in the oil, but it can be removed in the subsequent refining process, although some oil is lost. Meanwhile, some gossypol can react with other compounds in the... 

In the next step, fatty acids are separated from the oil by neutralisation (deacidification or afkahne refining) with sodium hydroxide solution (which is also effective in the removal of toxic gossypol from cottonseed oil see Section 9.11). The free fatty acid content varies widely within 0.5-1.5% in seed oils from raw materials grown in a temperate zone. After neutrahsation, the fatty acid content falls below 0.1%. The resulting soaps are separated as soap stock and typically used in animal feed. Tropical oils, such as palm and coconut oils, contain 3-7% free fatty acids. It is therefore preferable to separate the free fatty acids together with volatiles by distillation in the end stage of physical refining process. In this case, the main components of the distillate are free fatty acids. 

In food processing, the major objectives are sometimes achieved at the expense of some loss of recognised nutrients. However, in other cases, important nutrients may become available only after appropriate processing, since inhibitors or other interfering compounds may be destroyed or inactivated. Toxic factors can sometimes be destroyed by denaturation, as with enzymes, protease inhibitors and phyto-haemagglutinins. They can also be physically removed, for example by leaching, solvent extraction or solid classification methods, as in the removal of gossypol from cottonseed protein, or of phytate from cereals. 

The removal of gossypol from cottonseed can be achieved by physical separation in a liquid cyclone or by solvent treatments (Table 3). The latter so far have only succeeded at the expense of introducing... 

Dichloromethane or methylene chloride is an excellent solvent for oil extraction because of its low boiling point (39.8 °C), which makes desolventization of oil and meal easy. Furthermore, it is non-flammable and has low specific heat, latent heat of vaporization and low solubility of water. Utilization of dichloromethane for oil extraction was first demonstrated in the 1940s but the process was not economically feasible at the time because of the relatively high cost of dichloromethane. In 1986, the feasibility of cottonseed oil extraction by using dichloromethane was demonstrated at a pilot scale study (Johnson et ai, 1986). Residual oil content in the meal was lower than typically achieved with hexane extraction. Cottonseed meal produced during the process was suitable for use in poultry feed formulations, because gossypols present in cottonseed were extracted with oil and removed from meal. No residual aflatoxin was detected in alkali-refined oil. 

Cottonseed oil is a vegetable oil extracted from the seeds of the cotton plant after the cotton lint has been removed. It must be refined to remove gossypol, a naturally occurring toxin that protects the cotton plant from insect damage. In its natural unhydrogenated state, cottonseed oil, like all vegetable oils, has no cholesterol. It also contains no trans fatty acids. Further, these polyunsaturated fats can potentially go rancid during the extraction process. ... 

Cottonseed is the world s second oilseed crop in terms of volume after de-linting, it yields a seed rich in oil and protein. The oil is readily extracted by conventional methods, and has widespread food uses after refining. The residual protein-rich meal, however, has only very limited use because it contains gossypol (III), a yellow toxic substance which interacts with the protein, drastically reducing its biological value. The removal of gossypol from de-linted cottonseed has therefore been a prime industrial objective for many years. 

In processing most oilseeds, hexane is stripped from the miscella by distillation to produce a crude oil. However, gossypol and other pigments become extremely difficult to remove if left warm in cottonseed oil for more than a few days. It is common practice for cottonseed oil mills either to send their crude oil immediately to an alkali refinery or to have a miscella or alkali refinery on-site to arrest the fixing of color. ... 

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