1. How does interesterification occur?

The term interesterification refers to the exchange of acyl radicals between an ester and an acid (acidolysis), an ester and an alcohol (alcoholysis) or an ester and an ester (transesterification). It is the latter reaction that is relevant to the industrial interesterification of oils (also refered to as randomization) since it involves ester interchange within a single triacylglycerol molecule (intraesterification) as well as ester exchange among different molecules.

If one considers that two (n) fatty acids (A and B) are available to be esterified to glycerol, eight possible triacylglycerol species can result (n³).

Regardless of the distribution of the two acids in the original fat (e.g. AAA and BBB or ABB, ABA, BBA), interesterification results in the "shuffling" of fatty acids within a single molecule and among triacylglycerol molecules until an equlilibrium is achieved in which all possible combinations are formed. Quantitative proportions of the different species depend only on the amount of each acid in the original fat and can be predicted.