Elsevier

Food Chemistry

Volume 132, Issue 1, 1 May 2012, Pages 73-79
Food Chemistry

Glycidyl esters in refined palm (Elaeis guineensis) oil and related fractions. Part II: Practical recommendations for effective mitigation

https://doi.org/10.1016/j.foodchem.2011.10.034Get rights and content

Abstract

In a previous work, it was shown that at high temperatures (up to 280 °C) glycidyl esters (GE) are formed from diacylglycerols (DAG) via elimination of free fatty acid (FFA). In the present study, the impact of DAG content and temperature on the formation of GE using a model vacuum system mimicking industrial edible oil deodorization is investigated. These deodorization experiments confirmed that the formation of GE from DAG is extensive at temperatures above 230–240 °C, and therefore, this value should be considered as an upper limit for refining operations. Furthermore, experimental data suggest that the formation of GE accelerates in particular when the DAG levels in refined oils exceed 3–4% of total lipids. Analysis of the lipid composition of crude palm oil (CPO) samples allowed the estimation that this critical DAG content corresponds to about 1.9–2.5% of FFA, which is the conventional quality marker of CPO. Moreover, high levels (>100 ppm) of GE were also found in palm fatty acid distillate samples, which may indicate that the level of GE in fully refined palm oils also depends on the elimination rate of GE into the fatty acid distillate.

Highlights

► Glycidyl esters (GE) are formed during palm oil refining from diacylglycerols. ► Direction to limit formation of GE during palm oil refining are provided in the present study. ► Quality parameters to be monitored in crude palm oil order to limit GE formation are discussed.

Introduction

Over the past 5 years, strong evidence has been exhibited in the scientific literature for the formation of 3-chloropropane-1,2-diol (ME) and glycidyl (GE) esters during palm oil refining (Franke et al., 2009, Weissharr and Perz, 2010, Zelinková et al., 2006). It has been demonstrated that the formation of ME and GE is a direct result of the exposure of palm oil lipids to high temperatures, particularly during edible oil deodorization. The exact chemical pathways responsible for these compounds are under debate (Hamlet et al., 2011, Rahn and Yaylayan, 2011). Despite their unclear origin, the occurrence of these process contaminants in palm oil and related finished products has gained the attention of various regulatory and scientific groups due their potential toxicity (Habermeyer et al., 2011, Schilter et al., 2011, Seefelder et al., 2011, Weisshaar, 2011). Accordingly, as the ‘worst-case scenario’, their complete conversion into free MCPD (carcinogenic) and glycidol (carcinogenic and genotoxic) is assumed and pre-emptive mitigation is recommended (Matthäus, 2011). Effective mitigation of ME and GE in refined palm oil requires the detailed understanding of the mechanism involved in their formation during the refining process.

In a previous work, it was shown that at high temperatures (up to 280 °C) GE are formed from diacylglycerols (DAG) by elimination of a free fatty acid (FFA) residue (Destaillats et al., 2011). In addition, it was demonstrated that GE can be formed also through the dehydration of monoacylglycerols (MAG). This reaction route however, is quantitatively less significant since MAG levels in refined and bleached (RB) palm oil are quite low (i.e., ∼0.3%; [Goh and Timms, 1985]). In addition, MAG are removed during edible oil deodorization, and therefore, their contribution to the overall GE production is negligible.

High DAG contents ranging from 4% to 12%, with a mean of ∼6.5% have been reported in palm oil (Long et al., 2005, Siew, 1995, Siew and Ng, 1999). In a recent report, Hrncirik and van Duijn (2011) showed that even at relatively low deodorization temperatures (230 °C), chemically- or physically-refined palm oil can contain high GE levels (i.e. ∼2 ppm). Further, these levels can increase exponentially with increasing the deodorization time and temperature (Hrncirik and van Duijn, 2011, Weissharr and Perz, 2010). In this study, we further investigated the effects of deodorization temperature and DAG content on the formation rate of GE in palm oil in order to propose effective mitigation strategies. Furthermore, since the DAG content in refined palm oil is related to the quality of the upstream crude palm oil (CPO), we examined CPO quality parameters to be monitored in order to limit the occurrence of this GE precursor.

Section snippets

Samples and reagents

Pyridine (99% purity), and N,O-Bis(trimethylsilyl)trifluoroacetamide/trimethylsilylchlorosilane (BSTFA:TMCS 99:1, v/v) were obtained from Sigma–Aldrich (Saint Louis, MO, USA). Diheptadecanoin was obtained from Nu-Chek-Prep (Elysian, MN, USA). Glycidyl oleate, palmitate, linoleate, and linolenate were obtained from Wako Chemicals GmbH (Neuss, Germany). Glycidyl stearate was synthesized and purified according to a published procedure for the synthesis of glycidyl esters (see synthesis of glycidyl

Acknowledgments

The authors would like to acknowledge Dr. Walburga Seefelder, Dr. Pascal Zbinden, Dr. Olivier Schafer and Dr. Boon-Seang Chu from the Nestlé Research Center (Lausanne, Switzerland) for the interesting discussions about edible oil refining and the occurrence of process contaminants in refined oils. We also would like to thank Dr. Kalanithi Nesaretnam, Dr. Wai Lin Siew, and Raznim Arni Abd. Razak from the Malaysian Palm Oil Board (MPOB) Product Development and Advisory Services Division in

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