Some characteristics and functional properties of rapeseed protein prepared by ultrasonication, ultrafiltration and isoelectric precipitation

BACKGROUND: The presence of complex protein constituents and difficulties in extracting protein from rapeseed meal limit the application of rapeseed protein in food processing. However, double-low rapeseed (low erucic acid, low glucosinolate) protein is a type of complete protein that is of potential use in the food industry. In this study the characteristics and functional properties of rapeseed protein prepared by ultrasonic-assisted extraction, ultrafiltration and isoelectric precipitation were analysed and compared with those of soybean protein. RESULTS: The extraction efficiency with the ultrasonic-assisted method was significantly higher than that obtained with the traditional method. Ultrafiltration and isoelectric precipitation yielded three different proteins: ultrafiltered protein RPs and precipitated proteins RP5.8 and RP3.6. Chromatographic separation of RPs resulted in four fractions: RPsI, RPsII, RPsIII and RPsIV. The distribution of the isoelectric point of rapeseed protein was investigated by two-dimensional electrophoresis. The amino acid composition of RPs renders it suitable for human consumption. The hydrophobic/hydrophilic amino acid ratio of rapeseed protein was higher than that of soybean protein. The functional properties (oil adsorption ability, emulsifying capacity, foaming capacity and foam stability) of RPs, RP5.8 and RP3.6 were found to be better than those of soybean protein. CONCLUSION: Ultrasonication and ultrafiltration were significantly better than the traditional method of rapeseed protein extraction. The ultrafiltered rapeseed protein RPs had superior functional properties. The results of this study provide useful indicators for rapeseed protein as a potential replacement for other proteins. (C) 2011 Society of Chemical Industry