Molecular Reaction Mechanism for the Formation of 3-Chloropropanediol Esters in Oils and Fats.

Abstract

3-Chloro-1,2-propanediol fatty acid esters (3-MCPD esters) are a group of process-induced contaminants that form during the refining and heating of fats and oils. In this study, a combined method of simulated deodorization and computational simulation was used to explore the precursor substance and the generation path of 3-MCPD esters. From the results, 3-MCPD esters reached a content level of 2.268 mg/kg when the diacylglyceride (DAG) content was 4% and temperature was 220 °C. A good correlation was observed between DAG and 3-MCPD ester contents ( y = 0.0612 x2 - 1.6376 x + 10.558 [ R2 = 0.958]). There were three pathways for the formation of 3-MCPD esters: (A) a direct nucleophilic substitution reaction, (B) an indirect nucleophilic substitution reaction, and (C) a mechanism of an intermediate (glycidyl ester) from the calculation of Gaussian software at the B3LYP/6-31+g** level. The data showed that the ester-based direct nucleophilic substitution reaction was the most likely reaction pathway. The energy barriers for the formation of the 3-MCPD esters dipalmitin, diolein, and dilinolein were 74.261, 66.017, and 59.856 kJ/mol, respectively, indicating that the formation process of 3-MCPD esters is a high-temperature endothermic process. Therefore, by controlling the introduction of precursor (DAG) and reducing the temperature, 3-MCPD ester formation was prevented.