the cakes are classified into a) Ghani pressed
- b) Expeller pressed and c) Solvent extracted. Of these, ghani pressed cakes contain the maximum amount of ether extract, while solvent extracted contain traces of oil. Conversely the protein content is higher in solvent extracted cakes and lowest in the ghani cakes.
Oilseed cakes are in general very good sources of protein and about 95% of the nitrogen is present as true protein. Vegetable proteins are generally poorer compared to animal proteins. Proteins of oil cakes have a low glutamic acid, cystine, methionine and variable but low lysine content. The meals usually have a high phosphorus content which tends to aggravate their low calcium content. They may provide good amount of B vitamins but are poorer sources of carotene and vitamin A.
The high temperature and pressures of the expeller process may result in a lowering of digestibility and in denaturation of the protein with a consequent lowering of its nutritive value. The high temperature and pressure also reduces most of the deleterious substances which might be present in oilcakes such as gossypol and goitrin. Some seeds such as groundnut, cottonseed 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 removed by cracking and riddling a process known as decortication.