Interesterification
Despite the fact that there are a large number of vegetable oils, there are only a few oils that can give structure to a product. Therefore, it is often desirable to modify the melting properties of an oil. This is because the melting properties determine the hardness of an oil or fat at a particular temperature and have a major influence on the structure of the end product. This can be achieved by means of a number of technological modification processes.
By modifying an oil it is possible both to change the fatty acid composition and to change the distribution of the various fatty acids over the particular triglycerides. In both cases this leads to a different melting behaviour of the product in comparison with the original material. The functionality of the end product can be adjusted even better by not simply modifying a single oil but instead a mixture of selected oils.
Examples of technological modification processes are:
- hardening or hydrogenation
- fractionation
- interesterification
More information about these techniques can be found in the factsheet ‘Functions of fats’. This article will discuss the technology of interesterification further.
Process and result
The objective of interesterification is to improve the melting behaviour of an oil while retaining the same fatty acid composition.
A fat molecule, or triglyceride, consists of a glycerol molecule with three fatty acids coupled to it. The natural positional distribution of fatty acids in triglyceride molecules is not always the same. In vegetable fats the saturated fatty acids are found particularly on the first and third positions, termed the sn-1 and sn-3 positions. In animal fats (e.g. pig fat and milk fat) the saturated fatty acids are found in particular on the middle or sn-2 position. Palm oil is the only exception among the vegetable oils. In palm oil and palm oil stearins (see the chapter Fractionation) a relatively high amount of saturated fatty acids are also found on the middle position.
During the interesterification process these fatty acids are redistributed over the three positions in the molecule. This redistribution does not take place just within one triglyceride molecule but also between different triglyceride molecules. In order to carry out interesterification a catalyst is added to the original oil while it is warmed in a tank. The addition of the catalyst to the starting material causes the fatty acids to be uncoupled and then recoupled so that the various fatty acids in the oil are distributed evenly over all three positions. After a certain time the oil is cooled and the catalyst removed.
Enzymatic and chemical interesterification
Interesterification has been in use in the oils and fats industry for some time already and up till now a chemical catalyst has usually been used, but a development that is attracting a great deal of attention at present is enzymatic interesterification.
In this process instead of using a chemical catalyst an enzyme, lipase (the term means a fat-splitting enzyme) is used. Enzymes are large protein molecules that are constructed in a very ingenious manner (see the figure) so that they can induce reactions to take place under mild process conditions and at low temperatures. In this way more valuable substances remain intact in the oil. As well as this, the process does not generate much waste and it is better for the environment since as well as fewer chemicals less water and energy are used. The working of the enzymes in this process is comparable with the way in which fats are constructed in nature and then, in every living organism, decomposed as part of digestion.
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| Figure: a computer image of the three-dimensional structure of a lipase. | Figure: a triglyceride, consisting of a glycerol molecule with three fatty acids attached. The arrow shows where the lipase interacts. |
Natural digestive process
During the digestion of oils and fats in the small intestine of humans by means of enzymes, lipases, the fatty acid chains attached mainly to the sn-1 and sn-3 positions of the triglyceride molecules are removed (see the figure). This leaves not only free fatty acids but also monoglycerides (a molecule of glycerol with just one fatty acid attached) that are absorbed and processed in the body in a different way to the free fatty acids. Because more saturated fatty acids become positioned on the sn-2 position during interesterification it is suggested that this could as a consequence have effects on health.
Various nutrition studies in which a diet containing fats that had been treated by interesterification was compared to a diet containing fats that had not been so treated but with the same fatty acid composition have been carried out to research this. The results of all the studies in this field have recently been evaluated again in two review articles1,2, one of which was written by order of the Product Board MVO2.
The conclusion drawn in both of the reviews is that no significant health effects caused by interesterification either on acute or chronic parameters of cardiovascular diseases could be shown to exist.
References
1 Berry S.E.E. (2009), ‘Triacylglycerol structure and interesterification of palmitic and stearic acid-rich fats: an overview and implications for cardiovascular disease’, Nutr. Res. Rev., 22(1):3-17.
2 Baumgartner S., Mensink R.P. (2009), ‘Metabolic effects of interesterified dietary fat in humans: a literature review’, MVO report.
