3. Mechanisms
There are two proposed mechanisms for interesterification, both important.
Enolate Ion Formation. This mechanism supports that an enolate ion (II), typical of the action of a base on an ester, is formed. The enolate ion reacts with another ester group in the triacylglycerol molecule to produce a b-keto ester (III) which in turn reacts further with other esters to give other b-keto esters. In this way all ester groups may react and in the triacylglycerol will thus move around from their initial positions.
The same mode of action applies to ester interchange between two or more triacylglycerol molecules. The intra-ester ester interchange is believed to predominate in the initial stages of the reaction.
Carbonyl Addition. Here, the alkylate ion adds on to a polarized ester carboxyl producing a diglycerinate intermediate.
This intermediate reacts with another glyreride by abstracting a fatty acid, thus forming a new triacylglycerol and regenerating a diglycerinate for further reaction. Ester interchange between fully saturated S3 and unsaturated U3 molecules is shown below, as a model for the randomisation which occurs:
