Extraction and characterization of groundnut oil: effect of different storage conditions on its lipid oxidation and physicochemical properties

The effect of sunlight on the quality of groundnut oil in comparison with the same oil samples stored in the dark at room temperature was aimed to study. The oil samples were exposed to sunlight (34-40°C) and ambient storage (~24°C in the dark) for 90 days. The samples were collected every 30 days for the analysis of their physicochemical properties including peroxide value (PV), p-anisidine (p-AnV), total oxidation (TOTOX), thiobarbituric acid (TBA), free fatty acid (FFA), color, induction period on Rancimat and fatty acid composition. At the beginning of the experiment, the PV, p-AnV, TOTOX, TBA and FFA values of groundnut oil were 10.31 meq O2/kg, 4.39, 25.01, 0.99 and 1.49% respectively; color 1.40R, 22.00Y and induction time (IT) 5.33 h. After 90 days storage at room temperature, the PV, p-An-V, TOTOX, TBA and FFA values were respectively ranged between 10.31-21.32 meq O2/kg, 4.39-7.36, 25.01-50.12, 0.99-2.42 ppm and 1.49-2.64%; the color in the red and yellow unit 1.40-1.20R and 22.00-19.00Y respectively; and the induction time 5.33-3.77 h. However, the same parameters at the end of exposure to sunlight were ranged in the same order, between 10.31-43.47 meq O2/kg, 4.39-22.24, 25.01-109.18, 0.99-3.25 ppm and 1.49-5.83% respectively; the color in the red and yellow units 1.40-0.50R and 22.00-1.30Y respectively; and the induction time 5.33-0.03 h. Results also showed that the amount of linoleic and gadoleic acids significantly dropped under sunlight compared to dark at room temperature. Sunlight significantly reduced the quality of groundnut oil. This oil should be stored in the dark at room temperature.