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Food Safety Focus (110th Issue, September 2015) – Food Safety Platform

Fats and Oils – What Are They?

Reported by Mr. Arthur YAU, Scientific Officer,
Risk Assessment Section,
Centre for Food Safety

Fats and oils contribute to an important part of our diet. They are a source of essential fatty acids and a concentrated source of energy in terms of human nutrition. On the other hand, fats and oils can also provide distinctive flavours to food and provide unique and desirable functions during cooking. For example, oils are the frying media for deep fried food; and when making pastries, fats (shortenings) are added to prevent the flour and other ingredients from clumping together.

What Are Fats and Oils?

Some people think that fats and oils are different things. But in reality, they share a common chemical structure and similar properties. The difference is that those that stay solid at room temperatures are called fats while those that stay liquid at room temperatures are called oils. Chemically, each fat or oil molecule consists of three long strings of fatty acid molecules combined with a glycerol molecule. Fats and oils may originate from plants, land or marine animals. Fats and oils may contain small amounts of other minor components that are naturally present. As fats and oils are produced by organisms as a way to store energy, they are found in a wide range of plants and animals.

Oils are commonly obtained from oil producing plants like corn, peanuts, soya beans, vegetable seeds, olives, palm kernels, whilst fats are more commonly obtained from animal sources like milk (butter), beef (tallow), pork (lard), etc. Fats and oils can also be obtained from marine sources like fish. Although butter, margarine and cocoa butter contain fats, they are defined and specified separately under standards other than fats and oils by the Codex Alimentarius Commission, the international food standards and safety authority. The differences in the fatty acid molecules attached can contribute to the properties and stability of the fat.

Processing of Fats and Oils

During the processing of oils, crude oil is extracted from the raw materials through physical means (e.g. pressing), chemical means (e.g. extraction by solvents) or a combination of both methods. Many of them are then further processed so that the desired quality and properties can be obtained in the product. Undesirable and harmful substances in the raw materials, if present, can also be removed during processing.

In obtaining animal fats, fatty parts of the animals are melted in hot water or steam. The melted fat rises on top of the water and is removed, while the unwanted meat tissues settle to the bottom.

An example of soya bean oil processing
An example of soya bean oil processing

For obtaining oils from plant materials, the raw materials may first be prepared by sorting out those that are damaged, followed by cracking, grinding before being pressed and/or extracted with non-toxic solvents like hexane. The crude oil obtained can then be further processed as illustrated above.

In the next two issues, we will cover the role of fats and oils in food quality, safety, nutrition and health.