However, the application of this new invention very soon led to a new shortage situation, namely with respect to the raw materials for margarine making. It was under this stimulus that Normann, near the turn of century, invented the catalytic hydrogenation of fatty acids. The aim of hydrogenation is to covert a liquid vegetable or fish oil to a fat with butter like consistency, by reducing the degree of unsaturation in its component fatty acids.
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.). The amount of catalysts used in hydrogenation is usually about 10% of nickel on the weight of the oil for a fresh catalyst but rising to 1-2% for a poisoned or spent catalyst.
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.
By elimination of double bonds and by cis-trans isomerisation, hydrogenation of fats raises 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).
Margarine must also be a plastic as possible at lower temperatures, it must have sufficient solid glycerides at 21-27°C, that it may be formed and packed in the customary prints it should be able to hold its shape and not separate oil for a reasonable period of time at 27-32 °F and must melt completely at the temperature of the human body, on order not to be gummy in the mouth.
Hydrogenation 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.
Hydrogenation of margarine
