Polypeptide profile and functional properties of defatted meals and protein isolates of canola seeds

Laboratory-defatted meals from four types of canola seeds were analysed for protein profile by reducing and non-reducing forms of sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). In the absence of a reducing agent (2-mercaptoethanol), four major polypeptide bands (16, 18, 30 and 53 kDa) were prominent in similar ratios in all varieties, in the presence of mercaptoethanol, significant reductions in intensity of the major bands occurred, suggesting that the major polypeptides contained smaller units which were held together by disulphide bonds. Meals from Brassica napus seeds had higher protein solubilities than meals from Brassica rapa seeds. Meals with higher protein solubility values also had higher foaming capacity (FC) values. Generally, the acid-precipitated (pH 4.0) protein isolates (APPIs) had higher FC values than the calcium-precipitated isolates (CPPIs). On the other hand, the CPPIs formed emulsions with higher values of emulsifying activity index (EAI) when compared to the APPIs. The results indicate that variations in functional properties of protein isolates and meals between the four seed types were probably due to differences in protein conformation in aqueous solutions rather than differences in polypeptide composition. (C) 2001 Society of Chemical Industry.