Oxidation

Oxidation is a chemical process in which a substance loses electrons or reacts through an oxidation pathway, often involving oxygen. In food, oxidation can change colour, flavour, aroma, texture and nutritional quality. Some oxidation reactions are undesirable, while others contribute to controlled maturation and flavour development.

Examples of oxidation in food

• Cut fruit: enzymatic oxidation can cause apples, pears and avocados to brown when exposed to air.
• Fats and oils: lipid oxidation can produce rancid or stale flavours in oils, nuts and other fatty foods.
• Wine: controlled oxygen exposure can contribute to maturation, while excessive oxidation may produce flat or undesirable aromas.
• Vegetables: oxidation can affect pigments and flavour compounds during storage and processing.

How to slow unwanted oxidation

Limit unnecessary exposure to oxygen, use suitable packaging, store sensitive foods away from heat and light, refrigerate where appropriate and use antioxidants or acid treatments when suitable for the product. For cut fruit, lemon juice or ascorbic acid can help delay enzymatic browning.

Oxidation versus enzymatic browning

Oxidation is a broad chemical category. Enzymatic browning is a specific oxidation process involving enzymes such as polyphenol oxidase and phenolic compounds. Lipid oxidation is another distinct pathway affecting fats and oils.

Chef’s tip: Identify the type of oxidation before choosing a control method. Lemon juice may help delay browning in cut apples, but it does not address every form of oxidation in food.

Key distinction: Oxidation includes several different reactions in food; it is not always harmful and does not always mean that a product has become rancid.