Analysis and occurrence of dichloropropanol fatty acid esters and related process‐induced contaminants in edible oils and fats

Abstract

A new sensitive method for the indirect determination of ester‐bound 2,3‐dichloro‐1‐propanol (2,3‐DCP), 1,3‐dichloro‐2‐propanol (1,3‐DCP), 2‐chloro‐1,3‐propanediol (2‐MCPD), 3‐chloro‐1,2‐propanediol (3‐MCPD) and 2,3‐epoxy‐1‐propanol (glycidol) in oil matrices is presented. It is based on a mild alkaline‐catalysed release of chlorohydrins and glycidol, followed by a transformation of glycidol to monobromopropanediol (MBPD) according to a modification of the AOCS Official Method Cd 29b‐13 (3‐in‐1 method). The dichloropropanols are separated from the monohalogenated diols and the oil matrix by l/l extraction and determined separately by headspace gas chromatography‐mass spectrometry (GC‐MS‐HS). Both MCPD isomers and the glycidol derivative are derivatised with phenylboronic acid (PBA) and analysed by GC‐MS separately. Method validation was performed in an oil matrix using isotopic labelled esterified standards. Linearity was verified for all analytes (r2 > 0.998). The limit of detection (LOD) for all analytes was ≤5 μg/kg. The modified determination of ester‐bound MCPD and glycidol was tested for accuracy by analysing reference samples. All free and bound analytes were investigated regarding their stability against undesired alkaline‐induced transformation. It was also demonstrated that bound MCPD and bound DCP might be generated in oil by heat treatment in the presence of a strong chloride donor. The method was applied to the analysis of a variety of different edible oils. None of the two tested dichloropropanols was detected. By contrast and as might be expected, both bound MCPD and bound glycidol were consistently detected in refined oils.Practical applications: The presented application is suitable for the parallel determination of ester‐bound dichloropropanols and monochloropropanols and ester‐bound glycidol in edible oils and fats using simple techniques for sample preparation. It covers more analytes and is more sensitive than other previously reported methods. Substitution of the double sample preparation, (a part of the AOCS Official Method Cd 29b‐13), by determining a correction factor for a whole set of samples, may reduce the effort required for sample preparation and raw data analysis. Furthermore, the investigation of basic transformations that may occur during sample preparation can be helpful for a better understanding of the complex chemistry in MCPD and glycidol analysis. Similarly, the results from heating frying fat in the presence of aluminium chloride might help to understand the distribution of chlorohydrin isomers in heat‐treated oils and fats.Assumed heat‐induced formation pathways of ester‐bound chlorohydrins in an edible oil.