Author: tpotocnik
Last saved by: Gürbüzoglu, Meltem
Company: IHPS

Influence of Roasting Temperature of Pumpkin Seed to PAH and Aroma Formation
Košir I. J., Potočnik T., Slovenian Institute of Hop Research and Brewing 
SI-3310 Žalec, Slovenia

Pumpkin seed oil is a culinary specialty of eastern Slovenia and it is produced by pressing roasted, hulled pumpkin seeds (1). It is classified as a natural edible oil; however, it stands between so-called 'virgin oils' and refined oils since its production process involves a roasting step but no refining of the product from the first pressing (2). The roasting process is responsible for the generation of typical aroma of the end product. It has a very characteristic nut-like roast aroma. The compounds responsible for the flavour of Styrian pumpkin seed oil are various pyrazine derivates. However, high temperatures used during roasting process, can also lead to a formation of polycyclic aromatic hydrocarbons (PAHs). At high temperature, organic compounds are partially cracked to smaller unstable fragments (pyrolysis), mostly radicals, which recombine to give relatively stable PAHs. PAHs are also formed as a result of certain food preparation methods, for instance roasting. In our work we investigated the influence of increasing temperature during roasting on PAH formation and changes in composition of volatile compounds. Different temperatures of roasting, from 90 ºC untill 200 ºC have been used. For PAH analysis HPLC with fluorescence detection was used. The detection of volatile compounds based on a solid-phase microextraction of the headspace, followed by gas chromatography coupled with mass spectrometry. 
PAHs were not detected in samples of pumpkin seeds oils roasted to temperature of 150°C. From this temperature on five PAHs were detected. Their content increases with increasing temperature. At 200°C total PAHs content is 8,3 µg/kg, with phenantrene being the most dominant one with the concentration of 7,9 µg/kg, followed by benzo(a)pyrene with 0,3 µg/kg.  Phenantrene  belongs to a group of light PAHs, which are less stable and toxic than heavy PAHs like benzo(a)pyrene.
17 volatile compounds were identified for which different trends of increasing or decreasing can be noticed. 2-ethylpyrazine, 2,5-dimethylpyrazine and 2-ethyl-3,6-dimethylpyrazine are increasing with a rising temperature;  some other compounds (1-pentanol, heksanol, 2-butenal) are decreasing. 
As the results indicate it is safe to use the temperature of roasting up to 150°C. 
1. Murkovič M., Pfannhauser W. 2000, Eur. J. Lipid Sci. Tech., 102, 10, 607-611.
2. Fruhwirth O. G., Hermetter A. 2008, Eur. J. Lipid Sci. Tech., 110,7, 637-644.