Food lipids. Extraction, analysis and main components

Lipids, used as food or industrial fats, are made up of a heterogeneous group of chemical families including triglycerides (triacylglycerols), diglycerides, monoglycerides, phospholipids, free fatty acids, sterols, sterol esters, alcohols, pigments (carotenoids, chlorophylls), tocopherols, hydrocarbons... Biological lipids include triglycerides, fatty acids and phospholipids, as well as complex lipids such as phosphoglycerides, sphingolipids, glycolipids and polyketides. Fats are called "Oil" when they are liquid at room temperature, and "Fat", followed by the indication animal or vegetable depending on the origin of extraction, when they are solid (concrete) at a temperature of 15°C (see current regulations). This difference in physical state is due to their fatty acid composition. Oils are richer in unsaturated fatty acids than fats. Lipids are a family of compounds as essential to life as carbohydrates and proteins. They play essential roles such as :

• cell membrane constituents ;

• nutritional elements ;

• energy reserve ;

• thermal insulation...

1 g of fat provides 9 kcal or 37.6 kJ.

The term "fats" or "matières grasses" is reserved for triglycerides and refers to the oils and fats found in food products. In fact, fats are a complex mixture of lipids that fall into two main categories:

• saponifiable compounds (90 to 98%) react with an alkaline reagent (NaOH, KOH, etc.);

• unsaponifiable compounds (2-10%) that do not react with alkaline reagents.

This article is mainly concerned with the saponifiable fraction. It deals with the extraction and determination of lipids from :

• plant or animal matrices;

• processed food products;

• cosmetic or industrial products.

It describes the physico-chemical parameters characterizing fats and their dosages. It gives methods for determining major compounds. In most cases, the standards associated with the analytical determinations are quoted.

The unsaponifiable fraction is covered in article [P 3 327] .

A glossary and table of acronyms are provided at the end of the article.

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