Changes of rapeseed and linseed oil during processing

During processing of crude oil in a large oil mill, three samples each of r ape seed and linseed were investigated at each processing stage, i.e. press oil, solvent-extracted oil, mixed oil, and degummed/caustic refined oil. I n the case of rapeseed also bleached and desodorized oils (230 degrees C; 3 .0 mbar for 2 h) were investigated. Rapeseed and linseed oil showing the ty pical major fatty acids contained less than 1% trans-isomeric fatty acids ( trans fatty acids = TFA). Linseed oil had a similar TFA-concentration as ra peseed oil, and the concentrations did not change during the processing sta ges up to degummed/caustic refined oil, and were also unchanged in the blea ched rapeseed oil. Desodorization of rapeseed oil, however, trebled the TFA concentration to 0.58%. The detected tocopherol patterns were typical of r apeseed and linseed oils. There was no difference between mixed oil and deg ummed/caustic refined oil in the total concentration of tocopherols. Neithe r had bleaching any effect Rapeseed oil desodorization diminished total toc opherol concentration by 12% from 740 mg/kg to 650 mg/kg. Due to degumming/ caustic refining the phosphorus concentration of both oils decreased to le ss than a tenth compared to mixed oil. Other elements determined in degumme d/caustic refined rapeseed oil were not detectable (manganese < 0.02 mg/kg, iron < 0.4 mg/kg, copper < 0.02 mg/kg, lead < 10 mu g/kg) or only as trace s zink 0.1 mg/kg, cadmium 2 mu g/kg). In linseed oil, which initially showe d a higher trace compounds concentration, a significant decrease was found by degumming/caustic refining. Iron could not be detected. There were trace s of zinc, manganese, copper, lead, and cadmium. There was no difference be tween the acid values of rapeseed end linseed crude oil. Acid value decreas ed drastically already during the degumming/caustic refining stage. The cru de linseed oils had a higher peroxide value, anisidine value and diene valu e than the corresponding crude rapeseed oils. With peroxide values of less than or equal to 0.1 mEq O-2/kg found in almost all investigated rapeseed o ils, no effect of refining could be detected. The anisidine value showed an increase after bleaching. Desodorization trebled the diene value.