Preparation of Protein Isolates from Rapeseed Flour

Abstract

For separation of nutritionally and functionally distinct protein fractions from rapeseed flour, a successive three stage procedure extracting with water, .1N HCl at pH 2 and .02N NaOH at pH 10 has been developed. The water extract in the first stage contained mainly acidic and neutral proteins whereas the HCl extract in the second stage mostly basic proteins migrating toward the cathode during gel electrophoresis at pH 8.8. Proteins in the NaOH extract in the third stage were a mixture similar to that obtained by direct .01N NaOH extraction of rape-seed flour. The yield of protein after isoelectric precipitation was 11, 13, 42 and 61% for the three stage extraction with water, HCl and NaOH and for the direct NaOH extraction, respectively.High ash content of the HCl extract was reduced from 36% in the total solids to approximately 5% by an oxalic acid treatment. Protein fractions obtained from the first and second stage extractions contained higher levels of lysine, histidine and arginine than those from the third stage. A considerable amount of cystine was lost in a macropeptide portion in whey during isoelectric precipitation.