Hydrogenation is the reaction of a molecule (in our case fat, more specifically fatty acid) with a hydrogen molecule (H2). It is essentially the saturation of fat with hydrogen (lat. hydrogenium).
- saturated fat cannot be hydrogenated because all carbons are already fully saturated with hydrogen
- monounsaturated fat (MUFA) can be hydrogenated at the double bond site, where just two hydrogens are missing. One of the excess bonds loosens, the missing two hydrogen atoms bind up back, thereby artificially producing saturated fat
- polyunsaturated fat (PUFA) can be hydrogenated:
- partially (the process described will only happen in some locations with double bonds)
- completely (hydrogenation occurs at all such sites) – complete hydrogenation results in saturated fat
In the food industry, the process has been known since 1900 and spread in the 1950s. Partial hydrogenation of PUFAs (in vegetable oils) is very popular with manufacturers because it has various advantages for them:
- from the liquid state, the fat (oil) becomes solid, or at least solidified (such as in margarine) – therefore, hydrogenation of fats is sometimes called hardening.
- flour products (baked goods) in combination with such processed fat have a better look and consistency after baking
- partially hydrogenated PUFA is cheaper than alternative animal fat with similar properties
- the desired degree of hydrogenation (what portion of the unsaturated sites in the chain will be saturated) can control the desired consistency and other properties
- longer shelf life (possibility of frontloading, etc.) – cost reduction
- greater popularity with the customer due to longer durability even after opening
Thus, virtually all the semi-finished products, margarines, or any industrially produced foods (especially bakery products) contained such processed fats. The problem is that after such partial hydrogenation most of the remaining unsaturated positions (double bonds) remain in the trans configuration. Therefore, these products are unsuitable for frequent consumption.
Manufacturers have become accustomed to promote products emphasizing that they are unsaturated fats (and hence suitable as an alternative to saturated fat, with better balance in fat consumption as a result – such as butter vs. margarine). However the fact is that partially hydrogenated fats are certainly not a good alternative. Since this is long-term known thing (which, after decades, has also spread to public consciousness), manufacturers begin to use other methods as full hydrogenation or interesterification. Those methods do not produce trans fats, but the long-term health impact is not known yet.