Abstract
Rapeseed meal and pressed cake are protein-rich by-products from rapeseed after oil extraction. Because of the high protein content, these by-products are an important source of food protein. Their use is motivated by the current pressure on protein prices, increasing demand for functional ingredients, and remaining controversy over wider use of soy. During process development for protein extraction from rapeseed cake or meal, special attention needs to be given to compounds such as erucic acid, which can cause problems if consumed in high amounts. Erucic acid determination is critical to ensure safety, since protein extraction procedures could lead to concentration of this compound in the final product. This research compared differences in extraction (Soxhlet and Folch) and derivatization techniques to obtain the highest erucic acid yield from rapeseed protein products. Results showed that no erucic acid accumulation occurred in the protein during its extraction from the rapeseed cake. The Soxhlet procedure was superior to Folch, as it yielded the highest concentrations of erucic acid. Furthermore, with the Folch procedure, some natural cis-configuration of erucic acid converted to its corresponding trans-configuration (brassidic acid). The latter is important, as ignoring this phenomenon can lead to underestimation of erucic acid content in rapeseed protein samples.
Highlights
Rapeseed meal and pressed cake are protein rich by-products from rapeseed after oil extraction
Even though rapeseed strains grown in the EU (‘00-rapeseed’) have been developed to have low levels of these antinutritional factors, their determination in final concentrated products is critical to ensure safety, given that protein extraction and concentration procedures could lead to concentration of these compounds in the final products
The experimental sequence was performed as follows: First, it was checked if it was possible to differentiate retention time during gas chromatography mass spectrometry (GC-mass spectrometer (MS)) measurements between the standards for all three isomers of the erucic acid methyl ester. These compounds were determined in the various protein products, and extracted by the Folch procedure combined with different derivatization
Summary
Rapeseed meal and pressed cake are protein rich by-products from rapeseed after oil extraction. Rapeseed cake has according to certain sources a similar protein and fat composition as rapeseed meal [2], while other sources found that rapeseed cake contains slightly lower concentration of protein while having a marginally higher fat percentage [3,4]. During process development for protein extraction from rapeseed cake, special attention is given to the raw materials, since certain varieties of rapeseed can contain high levels of antinutritional factors such as glucosinolates, erucic acid, tannins, sinapine, and phytic acid, which can cause problems after consumption [7]. Even though rapeseed strains grown in the EU (‘00-rapeseed’) have been developed to have low levels of these antinutritional factors, their determination in final concentrated products is critical to ensure safety, given that protein extraction and concentration procedures could lead to concentration of these compounds in the final products. This research will focus on erucic acid (fatty acid 22:1 n-9 or 22:1 ω-9), among the antinutritional factors found in rapeseed cake
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