Thursday, 29 September 2016
Fruit Oxidation - Why do foods turn brown? - Science fair project - Antonio Agustin
Have you ever noticed that fruits turn brown when you cut them? They turn brown when they are in contact with the air. The fruit's skin protects them, but if it breaks or is cut or damaged the fruit goes brown faster. Fruits contain enzymes (polyphenol oxidase and catechol oxidase are two common examples) that react with the O2 and with iron or copper cofactors in the fruit. A cofactor is a component that is necessary for a certain enzymatic reaction to happen. The fruit starts to oxidize and turn brown. Electrons are lost to another molecule, in this case the air. In other words, it's like an edible rust on your food!
Antonio Agustin has done the following experiment to study the effects of different substances on fruit oxidation. Oxidation can be prevented or slowed down by not allowing O2 to get to the surface of the fruit or by reducing the oxidase enzymes in them. For example, cooking fruit destroys the oxidase enzymes in them but it's also possible to prevent browning or oxidation by covering the fruit to avoid its contact with air or by lowering the pH on the surface, that is making it more acidic.
Antonio covered the food with different substances to try to find which prevents the food from turning brown best and why.
He tested 4 foods: apple, avocado, potato and banana. He submerged them in different solutions: lemon juice, vinegar, clear soda, olive oil, water, salt water and a control sample.
After observing his experiment for a few minutes he came to the following conclusion. Lemon juice, vinegar and clear soda prevent food from turning brown quickly. These liquids are acidic, they lower the pH of the food surface. Olive oil also prevents from browning because it doesn't let the oxygen reach the fruit. Water and salt water are the least effective.
Acids prevent oxidation because they react with the O2 that comes into contact with the surface of the sample. Once all of the acid covering the surface has reacted with the O2 or it has washed off or degraded, the sample will start to go brown. Stronger acids, like lemon juice, can even destructure the oxidase enzyme. This means that the enzyme can no longer perform its original function.
Antonio showed great interest and dedication doing this interesting experiment and explained it well at the Science Fair.
Posted by S. Bastian