De-oiled rapeseed and a protein isolate: characterization of sinapic acid derivatives by HPLC-DAD and LC-MS

De-oiled rapeseed is a rich source of proteins and phenolic compounds. The phenolic compounds, namely sinapic acid derivatives (SAD), could occur as free sinapic acid, esterified (as sinapine, the choline ester of sinapic acid) and decarboxylated (as canolol) forms. Rapeseed protein preparations containing very low phenolic compounds have been the focus of our ongoing research. A precipitated rapeseed protein isolate is investigated for SAD such as sinapine, sinapoyl glucose, canolol using HPLC-DAD and LC-MS. Profile of the phenolic compounds of de-oiled rapeseed, press cakes and the precipitated protein isolate are compared. HPLC-DAD analysis indicated SAD; particularly sinapine is the main phenolic compound of all the substrates. The protein derivation process did not remarkably alter the profile of the investigated protein isolate.