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Blends (5%, 10% and 20%, w/w) of cold-pressed black cumin (Nigella sativa) oil (BCO) with sunflower oil (SO) were formulated. Oxidative stability (OxS) of SO and blends during storage at thermal accelerated oxidation conditions including Rancimat method (110C) and Schaal oven test (60C) was studied. Progression of oxidation was followed by measuring peroxide value (PV), conjugated dienes (CD) and conjugated trienes (CT). Changes in the volatile oxidation compounds, thymoquinone and tocopherols levels of oils and blends during thermal oxidation were also recorded. Blending did not affect significantly the fatty acids profile of blends wherein linoleic and oleic acids were the main constituents. Inverse relationships were noted between PV and OxS at termination of storage. Levels of CD and CT in SO and blends increased with increase in time. Nine volatile oxidation compounds including hexanal, (E)-2-hexenal, 2-heptanone, (E)-2-heptenal, 1-octen-3-one, 1-octen-3-ol, (E)-2-octenal, (E, E)-2,4-octadienal and (E, E)-2,4-decadienal were identified using the headspace/solid phase microextraction-gas chromatography/mass spectrometry (HS/SPME-GC/MS). Hexanal and (E)-2-heptenal were predominant identified compounds wherein these compounds increased during oxidation at 60C. Stability of blends was better than SO, most likely due to changes in the levels of thymoquinone and tocopherols' found in BCO. |
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