Linoleic Acid

Linoleic Acid
Linoleic Acid (also called cis,cis,-9,12-octadecadienoic acid) is an example of a poly-unsaturated fatty acid, due to the presence of two C=C double bonds. It is the main fatty acid found in vegetable oils such as soybean oil, corn oil and rapeseed oil.

It is used for manufacturing margarine, shortening, and salad and cooking oils, as well as soaps, emulsifiers, and quick-drying oils. The word linoleic comes from the Greek word linon (flax), and oleic meaning relating to or derived from oil.

Essential Fatty Acids
Linoleic acid belongs to one of the two classes of essential fatty acids that humans require. These acids are called "essential" because they can not be synthesised by the human body and must be eaten in food. If a person does not eat sufficient amounts of these essental fatty acid (i.e. at least a tablespoon day), they may start to suffer symptoms including dry hair, hair loss, and poor wound healing.

The two families of EFAs are ω-3 (or omega-3 or n-3) which comes from fish oils, and ω-6 (omega 6, n-6) which come from vegetable oils (linoleic acid is one of these). When they were discovered to be essential nutrients in 1923, the 2 families of essential fatty acids were designated as 'Vitamin F'. But around 1930, it was realized that they are better classified with the fats than with the vitamins, and so the name Vitamin F was dropped.

Margarine
In order to convert the liquid linoleic oil (and its triglyceride) into soft solid margarine, hydrogen is bubbled through the oil in the presence of a nickel catalyst under fairly mild conditions (175-190°C, 20-40 p.s.i.).

Hydrogenation in this way does a number of things. Firstly, hydrogen attaches to some of the double-bonded carbons, increasing the saturation level. In doing so, the molecules lose some of the rigidity associated with double bonds and so are able to flex. This allows them to pack closer together, raising the melting point, and turning the oil into a solid fat.

The removal of some of the reactive double bonds in this way also reduces the chances of attack by oxygen, so that the fat becomes rancid much less readily, increasing its shelf-life. Superheated steam is then passed through the molten fat to remove any impurities (especially bad-smelling acids and aldehydes).

But since this process also removes the coloration from the fat, artificial colouring agents made from carotenes of various kinds are added to make it appear yellow and buttery. Other additives include butanedione (to make it smell like butter), vitamins A and D, emulsifiers (to sharpen the flavour) and binding agents (lecithins) to hold the whole thing together.
Linoleic Acid