The study of some properties of rapeseed protein with a view to protein concentrate production

Optimum conditions for extraction and precipitation of rapeseed proteins have been defined: 10% NaCl extracts 70% of the total nitrogen (N t ) of a laboratory defatted flour and 0.1 N ‐NaOH, 89% (but only 62% of the N t of an industrial oil meal). The maximum precipitation of these proteins occurs at pH 3 (NaCl extract) and pH 6.5 (NaOH extract) with fairly low yields (22 and 51% of protein nitrogen, respectively). The explanation lies in the distinctive behaviour of two protein groups. The first one, composed of high molecular weight proteins, is readily precipitated by HCl; the second one, comprised of basic, low molecular weight proteins of excellent amino‐acid composition, is precipitated with great difficulty (trichloroacetic acid). Furthermore, the low protein yields generally reported also originate in important differences in solubility between laboratory defatted flour and industrial meal proteins, probably due to the denaturing action of heat and moisture used in oil‐processing.