What happens to cooking oil in the sun?

When cooking oil is exposed to sunlight, several chemical reactions and physical changes can occur:

1. Oxidation: Cooking oils are composed of triglycerides, which are molecules made up of fatty acids and glycerol. When exposed to sunlight, especially UV radiation, the fatty acids in the oil undergo a process called oxidation. Oxygen from the air reacts with the double bonds present in unsaturated fatty acids, leading to the formation of peroxides, hydroperoxides, and other oxidation products.

2. Rancidity: Oxidation in cooking oil can lead to the development of rancidity. Rancid oils have an unpleasant odor, taste, and appearance. The oxidation products formed during sun exposure react with other compounds in the oil, leading to the production of various volatile compounds responsible for the off-flavors and smells associated with rancidity.

3. Color Changes: Cooking oils may also undergo color changes when exposed to sunlight. Chlorophyll, a green pigment naturally present in some oils like olive oil, can break down under UV radiation, causing the oil to lose its green color and become more yellow or amber-colored. Other pigments in the oil may also degrade, further altering the oil's appearance.

4. Viscosity: UV radiation can affect the viscosity or thickness of cooking oil. As the oil undergoes oxidation and chemical changes, the molecular structure and composition can be altered, influencing its flow properties. The oil may thicken or become less viscous depending on the specific changes that occur.

5. Nutrient Loss: Cooking oils that contain essential vitamins and nutrients, such as vitamin E, may experience nutrient degradation when exposed to sunlight. UV radiation can cause the breakdown and loss of these nutrients, reducing the nutritional value of the oil.

To prevent these undesirable changes, it's important to store cooking oils away from direct sunlight. Oils should be kept in dark, cool places, preferably in opaque or UV-resistant containers. Proper storage helps maintain the quality, flavor, and nutritional value of the oils and prevents the development of rancidity.