Food chemistry


Apples soon turn brown when cut due to oxidation.

Atmospheric oxygen creates havoc for people in the food industry. Atmospheric oxygen quickly oxidises certain substances in food causing spoilage. Additives known as antioxidants are added to the food and mop up atmospheric oxygen before it can react with particular compounds in the food.

Ascorbic acid (vitamin "C" (C6H8O6)) is used as an antioxidant. It reacts with atmospheric oxygen according to the reaction below.

2C6H8O6(aq) + O2(g) -->2C6H6O6(aq) + 2H2O(l).

Most fruit salads contain apple. When apple is sliced it quickly oxidises and turns brown. Lemon juice, which is high in vitamin C, is often used to stop the oxidation taking place.

Fats are particularly vulnerable to oxidation by atmospheric oxygen. The double bonds, in some fatty acids, are attacked by atmospheric oxygen, this causes the formation of smaller, more volatile fatty acids that give off a rancid smell. Butter contains vitamin E, a natural antioxidant that is fat soluble. Vitamin E however, is unstable at high temperatures. To prevent oxidation of food subjected to high temperatures artificial antioxidants are used and they are clearly identified on the packaging by a number. Butylate hydroxytoluene is an artificial antioxidant and is identified on the packaging as additive 321.