Crop description. Gossypium spp., commonly known as cotton, belongs to the family Malvaceae and is native to the tropical and subtropical regions (see Fig. 4.4). Four separate domesticated species of cotton grown in various parts of the world are G. arboreum L., G. herbaceum L., G. hirsutum L., and G. barbadense L. Cotton shrubs are annual and found in the United States, Australia, Asia, and Egypt. Some have been grown for many years in southern Europe, mainly the Balkans and Spain. It can grow up to 3 m high [61-64].

Main uses. Cotton is a major world fiber crop. Its fiber grows around the seeds of the cotton plant and is used to make textile, which is the most widely used natural-fiber cloth. The seeds yield a valuable oil used for the production of cooking oil or margarine. The fatty acid composi­tion includes mainly palmitic acid (21%), stearic acid (2.4%), oleic acid (19.5%), linoleic acid (54.3%), and myristic acid (0.9%). Cottonseed oil, cake, meal, and hulls for feeding are other uses of the by-products. Whole cottonseed may be used as a feed for mature cattle. Cottonseed meal is an excellent protein supplement for cattle. The limitations on effective utilization of this product in rations for swine and poultry are of minor significance to ruminant animals. Cottonseed meal has a rel­atively low rumen degradability and is therefore a good source of by-pass protein and is especially useful in rations for milking cows [61-64].

Figure 4.4 Gossypium spp. (Photo courtesy of Prof. Jack Bacheler [http:/ /ipm. ncsu. edu/ cotton/InsectCorner/photos/ images/Open_cotton_plant. jpg].)

Kose et al. investigated the transesterification of refined cottonseed oil, using primary and secondary alcohols (oil-alcohol molar ratio 1:4) in the presence of an immobilized enzyme from Candida antarctica (30% enzyme, based on oil weight). The reaction was carried out at 50°C for 7 h, showing that conversion using secondary alcohols was more effective

[65] . Some authors have also proposed the use of lipase with methanol

[66] . Royon et al. used the same catalyst in a t-butanol solvent. Maximum yield was observed after 24 h at 50°C with a reaction mixture contain­ing 32.5% t-butanol, 13.5% methanol, 54% oil, and 0.017 g of enzyme per g of oil [67]. Recent tendencies propose the use of ultrasonically assisted extraction transesterification to increase ester yield [68].