Elsevier

Food Control

Volume 25, Issue 1, May 2012, Pages 355-360
Food Control

Detection and monitoring of 3-monochloropropane-1,2-diol (3-MCPD) esters in cooking oils

https://doi.org/10.1016/j.foodcont.2011.10.058Get rights and content

Abstract

A series of refined palm oil products were collected from different refineries in Malaysia and were analysed for 3-MCPD esters content. Samples were analysed using acidic transesterification and quantification by Gas Chromatography–Mass Selective Detector (GC–MSD). This method is based on the Federal German Institute for Risk Assessment (BfR) Method 008 for 3-MCPD esters. Limit of Detection (LOD) for this method was 0.25 mg kg−1 and Limit of Quantification (LOQ) was 0.50 mg kg−1 3-MCPD esters were generally not detected in crude oils, but were found at trace levels in bleached oils. Deodorized or fully refined oils contained higher 3-MCPD esters. The values ranged from <0.25–5.77 mg kg−1 for palm oil products, whilst other cooking oils in the retail ranged from <0.25–2.45 mg kg−1.

Highlights

► 3-MCPD esters was found in refined palm oil up to 5.8 mg kg−1 ► Crude oils showed levels from non-detectable to 0.9 mg kg−1 ► Fractionation of palm oil causes partition of the esters in the liquid phase.

Introduction

3-monochloropropane-1,2-diol (3-MCPD) fatty acid esters are food processing contaminants. They were first identified by Velisek et al. (1979) in model experiments based on lipids hydrolysed by hydrochloric acid. For many years, 3-MCPD esters have been known to occur in foods (Divinová et al., 2004, Svejkovská et al., 2004, Zelinková et al., 2006). In recent years, high amounts of 3-MCPD esters were also found in edible oils (Zelinková et al., 2006), and it was suggested that the mechanism of formation is linked to preliminary heat treatment of oilseeds and to the process of oil refining.

In fats and oils, 3-MCPD occurs in free and esterified forms (with fatty acids) (Seefelder et al., 2008) (Figs. 1 and 2). It was also reported that a major part of 3-MCPD is bound in the form of diesters. Refined olive and palm oils appear to be particularly prone to this contamination from heat-based processing. It is now clear that deodorization is the main culprit of the process-linked contaminant.

As palm oil refining is a physical process whereby free fatty acids are removed at the deodorization step, a higher temperature during deodorization is generally needed for good colour, odour and low fatty acid content. Fruit oils (olive and palm oils) appear to be more prone to such contamination than seed oils, the reason of which is still not clear. Although there is as yet no maximum tolerable daily intake (TDI) value for 3-MCPD esters in oils, it is nevertheless a particularly pressing problem for the oils and fats industry. In 2001, the Joint FAO/WHO Expert Committee on Food Additives has set a provisional maximum TDI of 2 μg 3-MCPD/kg body weight. In view of these developments, several methods of analysis have been developed by various organizations and researchers (Cost 927, 2005). Most methods are indirect involving release of 3-MCPD from the esters via transesterification in acid (BfR Method 008) or in alkali (DGF Standard Method C-III 18, 2009, Weiβhaar, 2008, BfR Method_82_FC-009–01, 2009, BfR Method_82_FC-010–01, 2009). After release, the free 3-MCPD is purified, derivatised and quantified using Gas Chromatography–Mass Selective Detector (GC–MSD). Direct measurements have also been developed using Liquid Chromatography–Mass Spectrometry/Time-of-Flight (LC–MS/TOF) (Haines et al., 2011). Hrncirik, Zelinkova, and Ermacora (2011) has identified the critical factors affecting the indirect measurements of 3-MCPD esters and made comparison of the alkaline and the acid transesterification approaches. Alkaline method is more sensitive to time of transesterification as observed by Hrncirik, whilst acid method is more consistent. Even different internal standards appear to behave differently. The pp-3-MCPD-d5 internal standard leads to higher results than the 3-MCPD esters type of internal standard. Another critical factor is the salting out chemical which is either sodium chloride or sodium sulphate. Alkaline transesterification method such as ‘BfR Method 009’ is more pH dependent and is also affected by the type of sodium salt used. The sodium chloride method gives a much higher result, due to the partial conversion of glycidol esters to 3-MCPD esters. For reasons mentioned above, acidic transesterification method was chosen for our analysis because it is more robust and provides a more realistic value of the 3-MCPD esters present in oils and fats.

The presence of these process-based contaminants in oils and fats has led to greater calls for information on the safety levels of contamination in different oils, factors causing the formation and mechanism of formation. High values in palm oil products recorded in the literature came from oil sources which were generally not identified or provided or of unknown history. As one of the major palm oil producing countries in the world, we recognize the importance of the issue, and are taking steps to monitor refined oils. This paper provides a comprehensive study of the oils at different processing steps of refining and of some cooking oils available in the retail market.

Section snippets

Chemicals and samples

3-monochloropropane-1,2-diol (98%, 3-MCPD) was purchased from Merck (Darmstadt, Germany), d5-3-MCPD (98%) from Cambridge Isotope Laboratories, Inc. (MA, USA), phenylboronic acid (PBA) was purchased from Merck (Darmstadt, Germany). Tert-butyl methyl ether (t-BME), sulphuric acid (H2SO4), sodium bicarbonate (NaHCO3), iso-hexane, cyclohexane and iso-octane of analytical and GC grades were purchased from Merck (Darmstadt, Germany).

Palm oil samples were collected from different refineries and stored

Effect of hydrolysis time

The acidic transesterification procedure was developed at BfR, Germany with a time of esterification of 16 h. For our study, the transesterification time was re-examined as there may be possible differences due to oil compositions. For example, palm oil and some fractions are higher in melting points than unsaturated liquid oils, and may require longer transesterification time. The method involves several steps; addition of an internal standard to the sample, transesterification, neutralisation

Conclusions

An acidic transesterification method based on ‘BfR Method 008’ was used for evaluation of samples of palm oil products. The study on hydrolysis time showed no significant effect on the area ratio of the 3-MCPD esters under acidic transesterification. Verification of the method showed that the percentage recovery for four concentration levels fall within the acceptable range (70–120%). A linear calibration curve was established with r2 ≥ 0.999, and LOD was optimized at 0.25 mg kg−1.

From the

Conflict of interest statement

The authors have declared no conflict of interest.

Acknowledgements

The research team wishes to thank the Director-General of MPOB for permission to carry out this work and also to publish this research effort. Special gratitude is dedicated to the staff of Food Safety Laboratory and Innovative Products Group for the analyses and supply of the oils.

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