Transesterification of fatty substances is a chemical process designed to redistribute fatty acids in triglyceride molecules;
Two main types of transesterification are known
- We talk about INTRAesterification when the transposition of fatty acids takes place within the individual glycerides of a fatty substance
- We talk about INTEResterification when the transposition of fatty acids occurs between the various glycerides of a mixture of two or more fatty substances
The simplest example to understand the potential of intersterification is to transfer part of the saturated fatty acids from palm oil triglycerides to the polyunsaturated counterpart of soybean oil. In this way it will be possible to increase the melting point of the soybean oil, which will appear as a "new", semi-solid fat at room temperature, from which it will be possible to obtain a vegetable margarine without the dreaded hydrogenated fats and a low fat percentage saturated.
In most vegetable fats, palmitic acid and stearic acid occupy (generally) the positions 1 and 3 of the glycerol molecule respectively, while any unsaturated fatty acids (such as oleic and linoleic) are typically in position two. Through transesterification we will obtain a fat with a higher percentage of saturated fatty acids in position two.
Instead of modifying the chemical structure of fatty acids as occurs with hydrogenation, transesterification provides to redistribute them in triglycerides, possibly using more than one lipid source, for example by engaging soybean oil (highly fluid at room temperature) and palm fat (completely concrete at room temperature).
It should be noted that intraesterification is also able to modify the solid-liquid balance of the triglycerides of an oil, since it depends not only on the acidic composition but also on the distribution of fatty acids within the triglyceride itself.
Transesterification can take place according to a chemical or enzymatic process:
- chemical interesterification - in the presence of basic catalysts, such as sodium methylate, and adequate temperatures - determines non-selective re-ordering of fatty acids (it is a randomized process with random distribution of fatty acids)
- the enzymatic interesterification, exploiting immobilized lipases of microbial or fungal origin, is commonly used by the industry for its selective modification of the position of the ac. fat in triglycerides (the process is therefore not random but targeted).
Critical issues
From the health food point of view, the most critical issues on interesterification processes derive from the quality of the raw materials of origin, which:
- they are refined (with the loss of part of the original food value)
- to contain costs they can be hydrogenated with the presence of trans fatty acids
- generally they are characterized by the presence of tropical vegetable oils, which due to their richness in saturated fats have a negative impact on blood cholesterol levels and more generally on cardiovascular risk
Furthermore, the exchange of natural positions of fatty acids raises doubts about the metabolic impact of these "altered fats". In fact, this change could have repercussions on cardiovascular health; Preliminary studies show that in this regard the impact of interesterified dietary fats on the levels of total cholesterol, LDL and HDL would be completely comparable to that of the natural counterpart.
