Lipid Oxidation

Lipid oxidation is a chemical reaction in which fats and oils react with oxygen, often accelerated by heat, light, metals and time. It can produce compounds responsible for rancid, stale, cardboard-like or warmed-over flavours. Lipid oxidation affects the quality and shelf life of oils, nuts, seeds, meat, fish and other foods containing fat.

What accelerates lipid oxidation?

• Exposure to oxygen during storage or processing.
• High temperatures, including repeated heating of frying oil.
• Light exposure, particularly for oils in transparent packaging.
• Trace metals such as iron and copper that can catalyze oxidation.
• High levels of polyunsaturated fatty acids, which are more susceptible to oxidation.

Examples in food preparation

Nuts and seeds can develop rancid flavours during prolonged storage. Reheated cooked meat may develop warmed-over flavour. Frying oil can deteriorate through repeated heating and exposure to air, food particles and moisture.

How to slow lipid oxidation

Store oils, nuts and seeds in sealed containers away from heat and light. Use suitable packaging, maintain good stock rotation and follow the operation’s oil-filtration and replacement procedures. Avoid overheating fats and do not mix fresh oil with severely degraded oil to disguise deterioration.

Lipid oxidation versus hydrolysis

Oxidation involves reactions with oxygen and can create rancid aromas. Hydrolysis involves the breakdown of fats through reaction with water, releasing free fatty acids. Both can contribute to oil deterioration but are different processes.

Chef’s tip: Monitor frying oil condition using the approved procedure, not colour or smell alone. Discard oil when it reaches the operation’s defined quality or safety limit.

Key distinction: Lipid oxidation is the reaction of fats with oxygen; it is not simply the melting or heating of fat.