Food Lipids . Analysis, quality, authenticity and minor compounds

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, if they are solid 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 an essential role in :

• cell membrane constituents ;

• nutritional elements ;

• energy reserve ;

• thermal insulation...

1 g of fat provides 9 kcal or 37.6 kJ.

The terms "corps gras" or "matières grasses" are reserved for triglycerides and refer 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 focuses on unsaponifiable compounds. It deals with the fractionation of unsaponifiable matter and the analysis of the various families of compounds that make it up: sterols, triterpenic alcohols, hydrocarbons, tocopherols, waxes, pigments and vitamins. It covers the determination of quality parameters and contaminants. It describes methods for authenticity testing.

The saponifiable fraction is the subject of the previous article [P 3 325] . As is customary in the industry, the percentages given are by mass, unless otherwise indicated.

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