Oilseed cakes and meals

Oilseed cakes and meals are the residues remaining after removal of the greater part of the oil from oilseeds.The residues are rich in protein (200-500 g/kg) and most are valuable foods for farm animals. The total usage of these products by the animal feed industry in Britain in 2008 was of the order of 2.6 million tonnes. This is similar to the figure of 2.7 million in 1999, but less than the 3.5 million tonnes used in 1991. 

Most oilseed residues are of tropical origin they include groundnut, cotton seed and soya bean. Some seeds such as castor bean yield residues are unsuitable for animal consumption because they contain toxic substances. 

Two main processes are used for removing oil from oilseeds. One uses pressure to force out the oil, and the other uses an organic solvent, usually hexane, to dissolve the oil from the seed. Some seeds, such as groundnut, cotton seed and sunflower, have a thick coat or husk, rich in fibre and of low digestibility, which lowers the nutritive value of the material. It may be completely or partially removed by cracking and riddling, a process known as decortication. The effect of decortication of cotton seed upon the nutritive value of the cake derived from it is shown in Table 23.2. 

Removal of the husk lowers the crude fibre content and has an important effect in improving the apparent digestibility of the other constituents. As a result, the nutritive value of the decorticated cake is raised significantly above that of the undecorticated cake. The latter is suitable for feeding adult ruminants only. In this class of animal, it may have a particular role in maintaining the fibre levels of the diets. Undecorticated cakes are rarely produced nowadays but partial decortication is widely practised. 

In the press process, the seed from which oil is to be removed is cracked and crushed to produce flakes about 0.25 mm thick, which are cooked at temperatures up to 104 °C for 15-20 minutes. The temperature is then raised to about 110-115 °C until the moisture content is reduced to about 30 g/kg. The material is then passed through a perforated horizontal cylinder in which revolves a screw of variable pitch that gives pressures up to 40 MN/m. The residue from screw pressing usually has an oil content of 25-40 g/kg. The cylindrical presses used for extraction are called expellers and the method of extraction is usually referred to as the expeller process. 

---

In developing low cost mass feeding foods, attempts were made to use locally available oilseed cakes and meals whenever possible. In time, interest turned to the extraction of high protein content... 

Oilseed cakes and meals are the residues remaining after oil is removed from oilseeds. 

Rapeseed has become an important crop in the temperate zones of the world, with production in more than 30 countries on 5 continents. The productive capacity of the crop and the nutritive value of its protein have made rapeseed a leading potential source of food and feed protein ingredients. Oilseed rapeseed was grown in India over 3000 years ago, and at least 2000 years ago in China and Japan. It is not clear when rapeseed oil became a food oil in addition to its use as a fuel for lamp lighting and for soap and candles. Throughout most of the long history of this crop, the cake or meal was used as a fertilizer or soil conditioner, a practice that persists today in China and Japan (5). 

Cake or meal from oil extraction contains 40-50% protein when processed in a screw press and 56-60% protein after solvent extraction. Sesame products have a pleasant flavor and contain high levels of methionine and cysteine. The flour produced from sesame meal has a high nutritive value compared to other oilseed flours (75). 

Palm kernel meal generally refers to the product obtained after solvent extraction of palm oil from the oil palm, whereas palm kernel cake is produced by mechanical extraction. In practice, the term palm kernel meal is often used to describe either product. This food has a comparatively low content of protein, and the balance of amino acids is poor. The first limiting amino acid is lysine. The ratio of calcium to phosphorus is more favourable than in many other oilseed residues. The meal is dry and gritty, especially the solvent-extracted product, and is not readily eaten it is therefore used in mixtures with more acceptable foods. Attempts to use it mixed with molasses, as molassed palm kernel cake, have not been successful. It has a reputation for increasing the fat content of milk, and its chief use is for dairy cows. Palm kernel meal has been described as being balanced for milk production, but in fact it contains too high a proportion of protein to energy. 

Similar to other oilseeds too, rapeseed contains not only oil, but also considerable amounts of proteins, polysaccharides, fibres and secondary plant substances. These compounds are to a different content located in the various seed compartments. After conventional oilseed processing, most of them must be enriched in the cake or meal. The protein content in rapeseed varies depending on the variety and conditions of cultivation and climate. Raw protein contents of 19-22% in rapeseeds and 31-36% in rapeseed meals can be obtained (Schwenke, 1994). 

Most of the grain milling residues and oilseed cakes are also used for feeding oilseed meals are particularly excellent feeds, containing 41-48% of crude protein. 

Solvent extraction. The press cake emerging from a screw press still retains 3 to 15 percent of residual oil. More complete extraction is done by solvent extraction of the residues obtained from mechanical pressing. The greater efficiency obtained in the solvent extraction process encouraged the industry for direct application to oilseeds. In the United States and Europe, continuous extractor units are used in which fresh seed flakes are added continuously and are subjected to a counterflow of solvent by which intimate contact is achieved between the seeds and solvent. The common solvent for edible oil is commercial hexane or heptane, commonly known as petroleum ethers, boiling in the range of 146 to 156°F (63.3 to 68.9°C). After extraction, maximum solvent recovery is necessary for economical operation. The solvent is recovered by distillation and is reused. The extraction oil is mixed with prepress oil for refining. The extracted meals contain less than 1 percent of residual oil. 

Sesame has declined in international trade due to a market preference for other oilseeds that are cheaper and easier to produce, such as groundnut. World trade tends to be in whole seed with only a small amount moving as oil and cake. There is great value in dehulling if the product is to be used as a foodstuff, as removal of the hull lowers the oxalic and phytic acid levels in the meal. The presence of these... 

Other options for recovery of oil from spent clay include mixing the spent clay filter cake with milled oilseeds en route to solvent extraction. This procedure is used in some refineries having associated crushing and refining plants and is convenient if the fire hazard of the spent clay can be overcome and the level of addition is small enough to not significantly alter the mineral content of the meal (99). 

Oilseeds are cmshed, Upid-protein bonds are destroyed by steaming, and the resnlt-ing material is expeller-pressed. Cakes obtained in this operation stiU contain 10 to 25% oil. Therefore, they are extracted with a solvent, primarily hexane. Other solvents are possible, bnt hydrocarbon solvents are cheaper. The extracted meal still contains 2 to 3% lipids but because it is used as feed, the residual lipids are utilized and are not objectionable. Crude oils obtained by expeller pressing and solvent extraction are usually mixed and refined. The first refining step in the removal of phospholipids (see Chapter 5) is the process called degumming. 

A theoretical extraction of oil and components from canola and oilseed rape, press cake/meal and/or deodizer distillate is illustrated in Figure 8.1. Manipulation of SC-CO2 operating parameters, including cosolvent choice and concentration, results in sequential or differential fractionation of these components and relative yields as described earlier and explored in the following sections using other plants as starting material for reference. 

---