Microwave-assisted saponification for the determination of 16 polycyclic aromatic hydrocarbons from pumpkin seed oils

The production of pumpkin seed oil requires a roasting of the pumpkin seeds, at temperatures generally higher than 60degreesC. The roasting at elevated temperatures produces the typical taste of the pumpkin seed oil but may also be the source of a contamination with carcinogenic PAHs. Owing to their lipophilic character, their bioaccumulation, and their toxicity these compounds should be subject to mandatory monitoring. Since there is a lack of norms and legal limits for hot-pressed oils, the limits set by the German Society of Fat Science of 25 mug/kg for the sum of 16 PAHs and 5 mug/kg for the heavy fraction for refined and cold-pressed oils, such as olive oil and others, have to be applied. Sample preparation was performed by microwave-assisted saponification with 1.5 M methanolic potassium hydroxide followed by a liquid-liquid extraction and purification with sulfuric acid. A final clean up procedure was performed on activated silica gel combined with a preparative Bondesil-cyano phase. For a selective measurement of the individual analytes, gas chromatography combined with mass spectroscopy was used in single ion monitoring mode. The overall analytical procedure was validated by systematic recovery experiments and by analyzing the certified reference material BCR CRM 458. Finally, this validated method was used for quality control of pumpkin seed oils from a producer co-operative.