Learn why ground sesame powder goes rancid relatively quickly. Discover how its high oil content is the cause and the best way to store it.
1 Answer
Sesame powder turns rancid over time primarily due to the oxidation of its unsaturated fats. These fats react with oxygen in the air, leading to the development of unpleasant odors and flavors.
Detailed Explanation:
Sesame seeds, and consequently sesame powder, are rich in unsaturated fatty acids. These fats are more susceptible to oxidation than saturated fats because they contain double bonds in their molecular structure. These double bonds are easily attacked by oxygen molecules in the air.The oxidation process is a chain reaction. It begins when a free radical (an unstable molecule with an unpaired electron) attacks a fatty acid molecule. This creates more free radicals, which then attack other fatty acid molecules, and so on. This chain reaction continues until antioxidants, if present, can neutralize the free radicals or until the fatty acids are completely oxidized.Factors that accelerate rancidity in sesame powder include:* **Exposure to Air:** Oxygen is the primary culprit in oxidation. The more sesame powder is exposed to air, the faster it will turn rancid.* **Exposure to Light:** Light, especially ultraviolet (UV) light, can catalyze the oxidation process, speeding up the formation of free radicals.* **Exposure to Heat:** Higher temperatures increase the rate of chemical reactions, including oxidation.* **Moisture:** While not a direct cause, moisture can promote the growth of microorganisms that can contribute to the breakdown of fats and the development of rancidity.* **Impurities:** The presence of trace metals or other impurities can also act as catalysts, accelerating the oxidation process.As the fats oxidize, they break down into smaller molecules, such as aldehydes, ketones, and carboxylic acids. These compounds are responsible for the characteristic rancid odor and flavor.
Pro Tip:
To extend the shelf life of sesame powder, store it in an airtight container in a cool, dark, and dry place. Consider storing it in the refrigerator or freezer for even longer preservation.