Enzyme-aided fractionation and analysis of rapeseed press cake components: Master's thesis

Rapeseed press cake is an industrial co-stream rich in proteins and antioxidative phenolics. While currently the material is used as feed, its components have potential use in food, health and skin care applications. Protein extraction from the press cake in mild conditions could be facilitated by disruption of the rapeseed cell walls using hydrolytic enzymes. The aim of the Master's thesis was to analyze the chemical composition of cold-pressed rapeseed press cake and to enrich proteins from the material by enzyme-aided technology. To select the enzymatic tools for protein enrichment, an analytical procedure was set up to obtain information on composition of the rapeseed press cake. The material was processed by sequential solvent extractions in order to produce fractions for analysis. The dry raw material contained up to 34% protein (N x 6.25, Kjeldahl total nitrogen analysis), 32% carbohydrates (HPAEC-PAD after acid hydrolysis) and 12% oil (gravimetric analysis after heptane extraction). The carbohydrates comprised 8% of soluble sugars, 5% of cellulose, 3% of pectin, 0.3% of starch and other polysaccharides. The enzyme-aided protein enrichment was carried out by treating the dry-milled rapeseed press cake with commercial cellulase, xylanase and pectinase preparations for 48 hours at 10% consistency, 30-50 °C and pH 6, using an enzyme dosage of 10 mg protein / g dry substrate. The hydrolysates were analyzed for solubilized sugars and proteins and the hydrolysis residues were characterized by microscopy. The pectinase preparation was the most effective enzyme in the release of reducing sugars, indicating the significance of pectin hydrolysis in cell wall disruption. Supplementation of the pectinase with cellulase or xylanase preparations did not considerably enhance the hydrolysis reaction. In addition, nearly comparable sugar yields were obtained by a lower enzyme dosage of 5 mg/g. The pectinase and xylanase were equally effective in the liberation of proteins or peptides. Due to significant protein hydrolysis caused by protease side activity in the xylanase product, the use of the pectinase preparation is favored when the aim is to release intact proteins. Additionally, the residual press cake after enzyme treatment was enriched in protein which was partially extractable in saline conditions (0.75 M NaCl in 0.05 M Tris-HCl buffer) at pH 8.5. After the successful preliminary experiments, further research will be carried out to obtain deeper knowledge on the mechanism of protein release during enzyme-aided extraction. The aim is to recover the solubilized and insoluble rapeseed protein fractions as protein-rich intermediates and to carry out high-consistency enzyme treatments in order to reduce water consumption in the processing