Changes in PAH levels during production of rapeseed oil

The influence of technological operations during rapeseed oil production on polycyclic aromatic hydrocarbon (PAH) concentrations in by-products, intermediate and final oils was evaluated. The decrease of light PAHs, benz(a)anthracene and benzo(a)pyrene during processing of crude oil to the deodorized product was significant at the 95% confidence interval in most batches analysed. Deodorization and alkali-refining were the steps contributing most to the PAH decrease. The relationship between PAH levels in rapeseed (and consequently in refined oil) and the duration of storage period was studied. The contamination of raw material processed a short time after harvesting was significantly higher than that of the rapeseed stored in silos for several months. Analyses of rapeseed samples, which were re-purified in the laboratory, revealed that solid particles, which contaminate rapeseed during harvesting, initial treatment, transport and storage, contributed to PAH contamination to the extent of 36% (light PAHs) to 64% (heavy PAHs) on average. Further experiments demonstrated that PAHs in re-purified rapeseed were concentrated in the cuticular layer, because they were removed well from the whole seeds by simple rinsing with organic solvent in an ultrasonic bath without losses of rapeseed oil. Alternative expressions of total PAH contamination (e.g. various PAH groups and/or differently defined B(a)P toxic equivalents) are discussed and their effect on drawing conclusions about PAH elimination rate has been demonstrated.