Misconception
In many cases partially and fully hydrogenated fats are banned from foodstuffs in Great Britain, although they are allowed. This is based on the misconception that trans fats are automatically produced during the process. This is not the case, but is unfortunately often the common perception. Research has shown that hydrogenation of fats can result in a product with an improved fatty acid composition and thus with a more favourable effect on the cholesterol level than a non-hardened fat with comparable functional properties (source: Mensink, 2007).
Ruminants
Hardening/hydrogenation of fats also occurs in nature, namely in the stomachs of ruminants. A limited amount of trans fatty acids is formed during this process, which is the reason for the presence of trans fatty acids in milk and meat and products derived from this such as butter.
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Factsheet Functions of fats in food
Modification of oils and fats
It is sometimes desired to change the properties of an oil. This is also called modifying oils and fats. By using the right kind(s) of oils and by processing these it is possible to influence the fatty acid composition and the functionality of the end product to a large extent.
For example, by modifying a type of oil the melting range of that particular oil can be influenced. This is because the melting and the crystallization properties of an oil or fat are related to the fatty acid composition and to the distribution of the various fatty acids over the fat molecules or triglycerides. Important here is that saturated fatty acids have a higher melting point than unsaturated fatty acids (saturated fatty acids are more solid than unsaturated fatty acids at room temperature) and within the group of unsaturated fatty acids monounsaturated fatty acids have higher melting points (are more solid) than polyunsaturated fatty acids. The functionality of the end product can be adjusted even better by not simply modifying a single oil but instead a mixture of oils.
Three processes are used in the industry to modify oils, namely:- hardening / hydrogenation
- fractionation
- interesterification
Hardening / hydrogenation
Thanks to hardening or hydrogenation it is possible to make fats with the desired solidity and the desired melting behaviour. Hardening or hydrogenation is a technique that has as aim changing the consistency of a fat. During this process hydrogen atoms are added to the unsaturated, double bonds in the fatty acid with the help of a catalyst. In the past trans fatty acids were produced during partial hydrogenation. Nowadays, only full hydrogenation is carried out and in this process no trans fatty acids are produced.
Fractionation
Fractionation is a technology whereby a fat is separated into different parts or fractions. Parts are separated off on the basis of different melting points of the different fractions, to produce products that have the desired functional properties or the desired fatty acid composition. Fractionation is usually used in order to separate the high melting point solid phase and the low melting point liquid phase of a basic raw material from each other. In this process an oil is cooled until crystals are formed. These crystals, that consist of triglycerides that will no longer dissolve in the rest of the oil, can then be removed from the oil using a filter. In this way two product fractions will always be formed, namely the high melting crystal phase, called the stearin, and the low melting oil phase, the olein.
Fractionation is often used with palm oil in order to produce palm olein (liquid) and palm stearin (solid). Palm olein contains a relatively large amount of unsaturated fatty acids and is used a great deal for frying. Palm stearin is used a great deal in margarines to give them the right consistency (spreadability).
Fractionation of palm oil into a stearine fraction and an oleine fraction (palm oil, stearine fraction, 1st oleine fraction).
Fatty acid composition of palm oil and fractionated palm oil (oleine and stearine).
Interesterification
During interesterification the fatty acids are redistributed over all the triglyceride molecules in the oil or in the mixture of oils. During the process the fatty acid chains are effectively cut off the glycerol molecules and then reattached resulting in a different distribution over the glycerol molecules. This changes the physical and functional characteristics of the oil so that properties such as the stiffness and the melting behaviour are improved while still retaining the same fatty acid composition. A catalyst is used to instigate the process. A development that is attracting a great deal of attention at present is enzymatic interesterification, a form of interesterification in which enzymes play the role of catalyst.
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Interesterification
