Influence of process conditions during aqueous protein extraction upon yield from pre-pressed and cold-pressed rapeseed press cake

As rapeseed is the third most important plant oil source worldwide (after palm and soya), vast amounts of residual press cake containing high amounts of valuable protein are generated during industrial de-oiling processes. Because the utilization of rapeseed press cake in feed and food is limited due to antinutritional factors, such as glucosinolates, alternative applications of rapeseed proteins in the non-food area are being investigated to add value to the rapeseed industry. However, a major problem remaining in protein extraction from de-oiled rapeseed residues is low protein solubility, resulting from thermal protein denaturation during industrial pressing. The aim of this study was to enhance protein yields from aqueous protein extraction by investigating the influence of various extraction conditions. Two different rapeseed raw materials were examined: cold-pressed meal (CPM) and pre-pressed meal (PPM). Factors examined were the solid to liquid (s:l) ratio, extraction time, temperature, pH value, concentration of sodium chloride, number of extraction cycles and the employment of protease. Best yields at mild ambient conditions were 52.3% for CPM and 36.7% for PPM, with the NaCl concentration being the most critical factor among the studied parameters. Interestingly, a simple extraction at native pH (5.7-5.8) gave comparable yields to extractions at pH 7-9. Improved yields were obtained under strong-alkaline conditions and by the employment of Protease A-01 with the limitation of protein hydrolysis occurring under these conditions. The best protein-extraction yields obtained from enzyme-assisted processes for CPM and PPM were 59.5% and 60.6%, respectively, for one-step processes and 80.7% and 78.3%, respectively, for three-step processes. The results obtained contribute to improving the sustainability of protein utilization from industrial waste streams. Thus, they support the ongoing effort to add value to the rapeseed industry within a biobased economy.