Two steps of dry fractionation: Comparison and combination of air classification and electrostatic separation for protein enrichment from defatted rapeseed press cake

A supercritical carbon dioxide-extracted rapeseed press cake (37% protein) was milled and subsequently fractionated either by electrostatic separation (ES) or air classification (AC) in one or two steps in different order. This novel approach was investigated to enhance protein enrichment and mass yield. After the first step, protein content and mass yield of the protein-rich fractions were 45% and 27%, respectively (ES) and 42% and 45%, respectively (AC). Combining ES as first step with AC as second step resulted in the highest overall protein content of 45%. Re-passing the protein-poor fractions increased the protein content from 32 to 37–38%, while ES and AC were used in different order and allowed to reach PSE up to 70% in this step. Furthermore, the composition, colour, particle size distribution, and protein solubility were characterized. Scanning electron microscopy images showed small protein bodies in the protein-rich fractions while the fibre-rich fractions contained larger particles.