The use of infrared spectroscopy for studying oxidation processes in pumpkin-seed oil

The study objective is to research the intensity of oxidation processes in unrefined pumpkin-seed oil of different types and producers, with the use of infrared spectroscopy method. Objects of the research are samples of traditional unrefined pumpkin seed oil of the following trade marks: Dial Export, Russia; «Pelzmann», Austria, and Styrian unrefined pumpkin-seed oil of Pelzmann trade mark, Austria. Fatty acid composition of the oils is researched with the use of Agilent 6890 Series and Agilent Technologies chromatographs, USA; qualitative composition of BAS (biologically active substance) is researched by chromatography-mass spectrometry method with the use of MAESTRO 7820A gas chromatograph, Private company with limited liability Interlab, Russia, with a mass selective detector of 5975 model. For the oxidation process study, oxidative stress is simulated by thermal influence during 4 hours at the temperature of 120 °С. Infrared spectrums are taken from infrared Fourier spectrometer every hour. The usage of infrared spectroscopy allows studying the formation of primary products oxidation on spectra changing in the area of 3000-3030 cm-1 (valence vibrations С-Н in cis-coupling -НС=СН-), and secondary products in the area of 3200-3700 cm-1 (ОН hydroperoxides and oxycompounds free group); 1500-1700 cm-1 (valence vibrations of С=О ketones and aldehydes group). It also allows to calculate the degree of oxidation on the following stages: chains conception (К1 and К2) and chains stopping (К3 and К4). Chain conception stage (К1 and К2) is more expressed in Styrian pumpkin-seed oil from Austria, but the chain stopping is mainly connected with changes in the area of 1500-1700 cm-1. As for traditional pumpkin-seed oil, independently on the producer, chain stopping is connected with the changes in the area of 3000-3030 cm-1, that signifies the different behavior of the final oxidation stage.