A new approach to dehulling

A novel approach to rapeseed dehulling utilises screw pressing of the hulls in order to raise oil yield and reduce the amount of anti-nutritional substances in the resulting rapeseed cake Michal Kaválek

Rapeseed is the world’s third most commonly grown oilseed, mainly popular for its canola cultivars low on erucic acid that can produce canola oil for human consumption.

Today, rapeseed/canola cultivation is widespread, especially in central and western Europe, Scandinavia, Canada, China and Australia.

Canola oil stands out for its low content of saturated fatty acids and a high content of unsaturated fatty acids.

Thanks to its mono- and polyunsaturated fatty acids ratio of 2:1, canola is a popular edible oil consumed for its cardiovascular and other health benefits.

For years, rapeseed products such as press cake or extracted rapeseed meal have also been utilised in the nutrition of cattle.

Since the ban on feeding meat and bone meal to livestock in the late 1980s/ early 1990s to prevent the spread of bovine spongiform encephalopathy (BSE) or ‘mad cow’ disease, the EU has seen a surge in the use of extracted rapeseed meal (RM) in animal feed.

With sufficient supply of RM and a goal of reducing dependency on imported soyabean meal, rapeseed meals have become widely used in dairy cow nutrition.

Today RM is a common component in feed mixtures and is distinguished by its high protein applicability which makes it, in many respects, a better feed choice than soyabean meal.

To a lesser extent, rapeseed products are also used in the nutrition of monogastric animals (pigs and poultry). This is mainly because they have a high content of fibre and digestibility-reducing substances such as glucosinolates.

Intensive dehulling process

Czech oilseed technology firm Farmet has an innovative rapeseed processing technology which focuses on eliminating the negative properties of rapeseed products.

The core of this technology consists of dehulling and expeller-pressing with extrusion. While all these technologies have been around for a number of years, the novelty lies in approaching the byproduct – the seed hulls.

In Farmet’s technological solution, seed hulls are also processed through screwpressing, which leads to a more intensive and efficient dehulling process.

The rapeseed goes through dehullers where the kernels and hulls are separated by being thrust against the stator of the dehuller. In the next step – the screen sorter and aspiration chamber – the hulls are separated out.

A high dehulling intensity results in a very clean main product. The kernels are distinguished by a high protein (≥ 50% in a defatted sample) and fat content, and a low amount of dietary fibre.

This product is subsequently pressed via a two-step pressing technology with extrusion. Apart from valuable oil, the other final output is a high-protein press cake, a valuable addition in compound feeds for monogastric animals (pigs and poultry). The cake resembles soyabean meal in its nutritional composition.

The hull fraction still contains a considerable amount of oil as a result of trapping some airborne kernels during aspiration and separation. However, this residual fat is by no means an issue.

In Farmet’s processing set-up, this fraction further enters a single-step pressing with extrusion technology. While the press cake coming out of this route does not reach the protein levels of the standard rapeseed press cake (see Table 1, following page), it represents a valuable feed source for ruminants, notably due its high content of soluble fibre and by-pass oil. There is also a considerable fraction of by-pass proteins.

The use of extrusion serves mainly to raise oil yield, reducing the amount of anti-nutritional substances and lowering the solubility of fibre. All of this increases the usability of the nutrients in rapeseed products. The technology thus yields three basic products: raw vegetable oil, a highprotein cake for monogastric nutrition, and a low-protein cake for ruminant nutrition.

Rapeseed cake

The practical experience of Russian edible oil and feed producer Sibirskaya Oliva has shown that utilising the higher residual fat content in rapeseed cake compared to rapeseed meal is no disadvantage; it is actually beneficial due to the cake’s higher energy value.

Moreover, the oil from the first pressing step is of a quality on a par with coldpressed oils, with a low phospholipid content and a high level of antioxidants and other valuable nutrients.

While the use of rapeseed press cake requires specific attention when planning feed doses, this approach promises to better utilise rapeseed/canola, as shown by field results shown in Table 1.

Farmet’s technology offers flexibility in rapeseed/canola processing, yielding a range of products ready to be fine-tuned according to the needs of particular livestock. This makes it easier to use locally-grown commodities for feed production, an increasingly important aspect of sustainable agriculture, which promotes local consumption of locallyproduced commodities. Michal Kaválek is R&D project manager at Farmet, Czech Republic DM = dry matter

Fraction size Protein Fat Fibre

High protein cake

44% 47% DM 8% DM 13% DM

Low protein cake

18% 26% DM 8% DM 28% DM

Crude vegetable oil

38% –

Table 1: Approximate values of fraction amounts and content ratios for nutrients in rapeseed products

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