Abstract
The loss of fats in the hulls is one of the main obstacles limiting the industrial implementation of rapeseed dehulling. The main reason resides in the shape of rapeseed outer cotyledons which resemble to the hulls’ shape and make it difficult to separate. The purpose of this study is to propose a new method for the purification of rapeseed hulls. After primary separation by aspiration, the mixture of hulls and kernels is passed between a pair of flat rolls where kernels are flattened and stick to the metal while the hulls do not. We exploited this property to adapt a small laboratory flaker with two counter-rotating cylinders of 65 mm diameter with scrapers that make the kernels fall away from the hulls. Process optimization by tunning experimental conditions (hulls moisture content, roller spacing, roller speed and feed rate) allowed the determination of the optimal operating conditions. Experiments showed that wetting improves the purity of the hulls but reduces the one of the recovered kernels. A gap of 0.1 mm was necessary. In addition, it was shown that the sorting quality depends on the ratio flow-rate / rotation-speed. The best performances are reached around 1 g.s−1.rpm−1. In these conditions, the hulls and kernels purity were 96% and 94% respectively. This preliminary work has allowed us to prove the concept. The next step will be to develop a pilot plant to validate the process efficiency on a larger scale (100 kg/h).
Highlights
France has decided to strengthen its autonomy in terms of plant proteins but cannot produce enough soybeans to satisfy the most demanding livestock systems in terms of protein concentration, so it must innovate to find acceptable substitutes (Terres Univia, 2020)
This study clearly showed that the composition of dehulled rapeseed meal is better suited to the poultry sector, which would capture 74% of the supply, while the sifted rapeseed meal with higher fiber content would be massively adopted by the swine sector (Lambert et al, 2021)
The price of dehulled rapeseed meal would have to be at 95% of standard soybean meal, which is roughly in line with the predicted values from a study we published in this same journal (Carré et al, 2015)
Summary
France has decided to strengthen its autonomy in terms of plant proteins but cannot produce enough soybeans to satisfy the most demanding livestock systems in terms of protein concentration (dairy cows, broilers), so it must innovate to find acceptable substitutes (Terres Univia, 2020). Even if the protein content of dehulled rapeseed meal does not reach that of soybean meal (> 46% protein), the qualitative leap is sufficient to make it a raw material of great interest for animal feed. This study clearly showed that the composition of dehulled rapeseed meal is better suited to the poultry sector, which would capture 74% of the supply, while the sifted rapeseed meal with higher fiber content would be massively adopted by the swine sector (Lambert et al, 2021). This adoption would make it possible to avoid importing non-GMO meals (soybean and sunflower). These thick-walled cells make this oil not very extractable and this contributes to the fact that rapeseed meal always has a higher oil content than sunflower and soybean meals (2.4% versus 1.1% and 1.5% for rapeseed, sunflower “35” and soybean meals, Tormo et al, 2020, 2021; Heuzé et al, 2020)
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