Antioxidant

An antioxidant is a food additive that slows oxidation, preventing fats from turning rancid and cut fruit from browning. Malay: antioksidan · Chinese: 抗氧化剂.

Oxygen in the air attacks food in two familiar ways: it makes the fats and oils go rancid, and it turns the cut surface of fruit brown. An antioxidant is added to slow these oxidation reactions down. It reacts with oxygen more readily than the food does, so it is oxidised first and protects the food, keeping the taste, smell and colour fresh for longer. This is why antioxidants are put into oily and fatty products in particular, and why a squeeze of lemon juice, which contains vitamin C, keeps a cut apple from browning.

Example. Vitamin C and vitamin E are natural antioxidants, and BHA and BHT are synthetic ones added to cooking oil, butter and packaged snacks. They react with oxygen ahead of the fat, so the fat stays fresh and does not develop the sour smell of rancidity.

Confusion to avoid. Do not confuse an antioxidant with a preservative. An antioxidant slows oxidation, the cause of rancidity and browning; a preservative slows the growth of microbes, the cause of rotting and mould. Both extend shelf life, but they act on different processes, so match each additive to the right kind of spoilage.

The antioxidant is studied alongside rancidity in the food additives section, so the two terms usually appear in the same SPM Chemistry question, connecting oxidation chemistry to everyday food preservation. A neat way to remember how it works is that the antioxidant sacrifices itself: it is oxidised in place of the food, taking the oxygen that would otherwise attack the fat. When you answer, state the purpose, to slow oxidation, and the result, that the food stays fresh and does not turn rancid or brown, so both halves of the idea are on the page.