Changes in chemical composition of some oils extracted from seeds roasted at different temperatures

Oil seeds are commonly used in cooking, frying and as salad oil and have commercial and economic importance. Since the seeds are roasted before pressing of the oil, changes occur in their composition; thus it is crucial to modify roasting process to minimise adverse effects. This study reflects the effects of different roasting temperatures (90, 150 and 210°C for 10 min. in conventional oven) on the oil constituents and some chemical properties of oils from the seeds of sesame, sunflower, soybean, flaxseed and poppy along with comparison to those of unroasted corresponding seed oils. Lipids from roasted seeds of sesame, flax and soybean exhibited relatively higher viscosity and free fatty acids, than lipids from unroasted seeds. With an increase in roasting temperatures the colour of the oils were slightly darker even though the changes were not significant in most cases. The content of α- and γ-tocopherols in oils (except soybean oil) gradually decreased as roasting temperature increased. β-tocopherol was higher in the oils of roasted seeds, while the amount of δ-tocopherol showed different trends with roasting depending on the type of seeds. For sesame and poppy oils, after roasting at 210°C, stearic and oleic acids showed higher percentages when compared to the levels in oils roasted at 90 and 150°C.