Assessment of oxidative deterioration of soybean oil at ambient and sunlight storage

This study was carried out in order to probe the extent of oxidative alterations in soybean oil (SBO), subjected to ambient and sunlight storage, over a period of 180 days. The magnitude of oxidative changes was monitored by the periodical measurement of peroxide value (PV), color, free fatty acid (FFA) contents, refractive index (RI), p-anisidine-, conjugated dienes-, conjugated trienes-, and iodine- values. At the end of storage period (180 days), the initial contents of FFA (0.02 % as oleic acid) and PV (0.02 meq/kg of oil) of the SBO samples subjected to ambient and sunlight storage reached the level of 1.77, 2.90 % and 20.52, 41.89 meq/kg of oil, respectively. The initial values of RI (40°C) (1.4630), panisidine (1.10), conjugated dienes (0.08) and conjugated trienes (0.04) rose to the point of 1.4647, 1.4659; 36.13, 50.40; 23.97, 41.49 and 13.81, 19.35, respectively. Whereas, the iodine value (g of I /100 g of oil) decreased from 138.00 to 126.18 and 118.04, respectively. At the end of storage period, the overall order, indicative of the oxidative changes in RI, FFA, IV, color (red + yellow), PV, P-anisidine, conjugated dienes and conjugated trienes of the SBO subjected to ambient and sunlight storage was as follows: 1.001:1.002, 1.00:1.65, 0.91:0.86, 0.80:0.60 + 0.75:0.50, 1.00:2.04, 1.00:1.39, 1.00:1.73 and 1.00:1.40, respectively. The results of various parameters investigated in the present study demonstrated the magnitude of oxidative deterioration of the SBO samples exposed to sunlight to be significantly (P < 0.05) pronounced as compared with that of ambient.