In the refining process for edible oils conditions must be carefully controlled to avoid the formation of toxic process contaminants, such as 2-MCPD, 3-MCPD, Glycidol and their fatty acid esters. An automated GC/MS-method now enables highly efficient determination of these compounds based on standard methods.
The European Food Safety Authority (EFSA) has recently updated their risk assessment for 3-monochloropropanediol (3-MCPD), 2-MCPD, fatty acid esters of these compounds, as well as glycidyl fatty acid esters (GE) in food. The result is based on data submitted by 23 member states: “Glycerol-based process contaminants found in palm oil, but also in other vegetable oils, margarines and some processed foods, raise potential health concerns for average consumers of these foods in all young age groups, and for high consumers in all age groups.” According to the press release: “The highest levels of glycidyl esters, as well as 3-MCPD and 2-MCPD (including esters) were found in palm oils and palm fats, followed by other oils and fats. For consumers aged three and above, margarines and ‘pastries and cakes’ were the main sources of exposure to all substances.” Incidentally, the FDA refers to GE as glycidol fatty acid esters.
Glycerol as building block
All fats and edible oils contain glycerol in the form of fatty acid esters (triglycerides). Not all oils are ready for the consumer in their native form; processing is generally required to remove off odors and to ensure sufficient shelf life. For deodorization, as part of the refining process, steam is used to gradually heat the oil under vacuum to around 200 — 230 °C to ensure that unwanted flavor and taste-intensive compounds are removed along with other unwanted VOCs and even pesticides. When chloride is present, heat treatment accelerates the substitution of fatty acids in triglycerides with chlorine atoms, leading to the formation of 2-MCPD and 3-MCPD fatty acid esters. Under these conditions, 1,3-diglycerides also react to form the glycidyl fatty acid esters.
Assessing the risk
The EFSA risk assessment of the above-mentioned glycerol derivatives is based on findings from animal experiments: In rats that had been fed 3-MCPD, cell changes were found, especially in the kidney area. Higher dosages led to benign tumors, as reported by the BfR in Berlin. According to the EFSA, the tolerable daily intake (TDI) value is 0.8 µg per kg body weight for 3-MCPD; due to a lack of adequate toxicological information, no assured TDI value for 2-MCPD can be given.
The risk assessment of glycidyl fatty acid esters is based on the assumption that these are fully transformed to free glycidol in the body. Since the free compound is known to be both genotoxic and carcinogenic, the experts from the panel on contaminants in the food chain (CONTAM) organized by EFSA could not provide any guidance on a safe level of glycidyl fatty acid esters. When a safe level doesn’t appear to exist, there is all the more need for action toward minimizing the level of these contaminants in order to minimize any health risk to consumers, and especially to infants who are not breast fed and therefore given industrially processed baby foods. Monitoring of these crucial levels requires adequate methods of chemical analysis.
Challenge for the analysis
For the determination of 2-MCPD, 3-MCPD, their fatty acid esters as well as glycidyl fatty acid esters and free glycidol, respectively, internationally, the ISO 18363-1  and the AOCS Cd 29c-13 methods are widely accepted. In Germany, the German Society for Fat Sciences (DGF) recommends a unified method, DGF C-VI 18 (10). The mentioned methods are all based on the use of gas chromatography with mass spectrometric detection (GC/MS).
The DGF unified method C-VI 18 (10) is almost identical to the AOCS Cd 29c-13 method. Both offer a solution to the problem: 3-MCPD fatty acid esters (bound 3-MCPD) are determined together with free 3-MCPD following alkaline hydrolysis and derivatization with phenylboronic acid. These unified methods also enable indirect determination of glycidyl esters (bound glycidol) by determining the difference between the free glycidol and total glycidol concentrations. This in short highlights the added value of the unified DGF C-VI 18 (10) and the AOCS Cd 29c-13 methods. These methods enable the determination of free glycidol in the sample and reading through them provides a fair impression of the effort required to transform the compounds such that they can be determined by gas chromatography, in this case relying on a manual sample preparation process that includes hydrolysis, extraction and derivatization.
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