RAPE (Brassica napus L.)

Importance and grain composition:

Rape is raw material for food production, namely edible oil. For animal feeding extracted meals and cake are used for compound feed manufacturing. It can also be used as fodder. Green matter is used as green manure. Rape oil us used as raw material in the chemical industry and it may serve as a renewable energy source, instead of fossil fuels. Rape is also utilized as honey-bearing plant.

Rape seed contains 35-40% fat, crude protein content is relatively high (about 20%). Biological value of protein is relatively good. Nitrogen free extract is low (only about 5%) crude fibre content is 7-12= and content of minerals 2-3%a- rape seed contains a considerable amount antinutritional substances, The most significant ones are glucosinolates, sinapines, erucic acid, and other substances such as antinutritional polysaccharides.

Glucosinolates are glycosides and their molecules contain sulphur. In the rate seed there are about 110 kinds of glucosinolates, gluconapine andprogoitrine prevail. Glucosinolates alone are not toxic, but toxic products are formed by their hydrolysis. The main hydrolysis products are thiocyanates, isothiocyanates and goitrin. Some of these compounds cause stinging, pungent and bitter taste perceptions and decrease feed palatability. They can also be transferred to animal origin product and influence the taste of milk and eggs. The effect on meat taste  has not been reported. They can also have strumigenous effect in birds and mammals. With an increased glukosinolate intake percentage of iodine captured by the thyroid decreases. Levels of triiodtyronine and tyroxine drop which causes a higher stimulation of the thyroid leading to thyroidism (hypertrophia). Administration of dietary iodine supplements cannot mitigate this effect. Another serious consequence is the liver damage manifested by liver hemorrhages. In particular poultry is susceptible , an increased intake of glucosinolates may even lead to death. Also fertility disorders may be caused in livestock, the mode of action, however, is not known. In man, a favourable effect of some glucosinolate hydrolysis products has been observed that activate enzymes detoxifying dietary carcinogenic compounds thereby decreasing the risk of colon cancer.

Sinapines are esters of choline and sinapic acid and other related phenolic acids. Their contents vary depending on variety and environmental conditions, an increases with seed maturing. They are not contained in leaves. Sinapines, and to a certain extent sinapic acid as well, cause bitter or tart taste of rape seed, oil and extracted meal which may decrease feed intake in animals. Phenolic acids form indigestible complexes with essential aminoacids and proteins thereby decreasing their digestibility. In some breeds of brown egg layer (e.g. Rhode Island Red) they cause a fish-like odour of yolk. This is caused by a genetic defect leading to insufficient activity of trimethylaminooxidase. The odour carrier is trimethylamine formed from choline that is under normal circumstances oxidized by trimethylaminoooxidase to odourless trimethylamine oxide. Thy enzyme is inhibited by goitrin formed from the glucosinolate progoitrine present in seeds. Nowadays, sinapines are removed by sequential extraction with alcalic diluents.

Erucic acid (22:1) is unsaturated fatty acid with various adverse effects on the organism such as myocardium damage, impairment of oxidative phosphorylation, negative effects on the growth in young animals.

In order to decrease contents of antinutritional substances, genetic improvement has been carried out. First, varieties with decreased erucic acid content (0) were grown, later varieties with decreased contents of both erucic acid and glucosinolates (00) that prevail nowadays.

 Cultivation requirements:

Both winter and spring forms are grown; in the Czech Republic winter rape prevails being the most important oil crop in this country. Rape does the best on deep loamy soils, with sufficient supply of humus, calcium and magnesium, pH 6-6.5. Light soils can be used only with good agrotechnology, shallow soils only when sufficiently fertilized. Winter rape does not tolerate heavy soils inclined to lumping. It is sown in August. Suitable previous crops are winter barley, spring mixtures, clover. All the crops that do not enable sowing in August are not suitable. Usually, rape is grown between two cereals because it mitigates the negative biological effect of high proportion of cereals on the arable soil.

Spring rape is grown mainly in the areas with tough winter (Canada), where the winter rape would not survive winter, and, on the contrary, in warm areas (Australia, India, China) where the cool season is missing. In this country, spring form is used only as a supplementary crop. As compared with the winter rape, the spring rape gives lower yields, lower oil content the protection against pests is more difficult.