Glycidyl esters in refined palm (Elaeis guineensis) oil and related fractions. Part I: Formation mechanism

Glycidyl esters (GE) are process contaminants generated during the deodorisation step of edible oil refining. In particular, GE are found in high abundance in refined palm oil. Palm oil is unique in that it contains a high amount of diacylglycerols (DAG, 4-12%). In the present study, a series of model reactions mimicking palm oil deodorisation has been conducted with pure tri-, di- and mono-acylglycerols (MAG). Results showed that GE are formed from DAG and MAG, but not from TAG, at temperatures (T) above 200 °C. Our observations suggest that GE are formed predominantly by intramolecular elimination of a fatty acid from DAG. In addition, isomers of GE, formed from DAG heated at T > 140 °C, were identified as oxopropyl esters. These new isomers were found to represent approximately 10% of GE levels in refined palm oil. Based on these considerations, the final GE content of palm oil could be limited by reducing DAG levels before oil processing and minimising deodorisation temperatures.