Effect of Long-Term Storage in Light and Dark at Room Temperature on Physicochemical Characteristics of Some Vegetable Oils

This work aims to study the effect of light and darkness during storage (12 months) on some edible oils (palm, sunflower, and soybean) on their physicochemical characteristics, oxidative stability and shelf life. The samples were stored in transparent PET bottles in the presence of light (Under illumination light 800 Lux) and darkness at room temperature. The effect of oxidation on oils during storage under light or darkness was evaluated the free fatty acid, peroxide value, thiobarbituric acid test, induction period, and the fatty acids composition, tocopherols, and tocotrienols. The induction period of the oil samples was 27.4, 9.50, and 5.10 h for palm, sunflower, and soybean oils, respectively. The percentages of free fatty acids increase with increased storage time; the highest values in light storage were (0.25, 0.70, and 0.85%) while in dark storage, they were the lowest (0.18, 0.37, and 0.41%) for palm, sunflower, and soybean oils, respectively.  As a result, light leads to an accelerated breakdown of unsaturated fatty acids, causing palm, sunflower, and soybean oils to form hydroperoxides of 7.7, 11, and 11.9 meq O₂/kg oil, respectively. In contrast, samples stored in the dark produced 5.5, 7.5, and 8.9 meq O₂/kg oil, respectively. The values of the thiobarbituric acid were (7.53, 17.74, and 19.19 mg malonaldehyde kg1) in the samples stored in the light than in the dark (5.41, 11.85, and 13.34 mg malonaldehyde kg1 for palm, sunflower, and soybean oils, respectively). The results showed that artificial light deteriorated the quality of the oil samples faster than that stored in dark conditions. On the other hand, the dark storage slowed down the breakdown of tocopherols, which protected the unsaturated fatty acids from oxidation. The findings demonstrated that oils degraded during storage more quickly in the presence of light than in the absence of light. The presence of saturated fatty acids, tocopherol, and tocotrienol in palm oil contributes to its stability.