3-MCPD and 3-MCPD fatty acid esters
3-Monochloropropane-1,2-diol (3-MCPD) is a contaminant in food that forms as the result of certain manufacturing methods. So far this substance has been found in few foods only, such as soy sauce or strongly toasted bread.
Along with free 3-MCPD, higher concentrations of MCPD fatty acid esters were found some years ago in a number of refined edible oils and fatty foods, such as infant milk formulas and hazelnut spreads.
1-Stearoyl-3-MCPD (example of a monoester):
1-Palmitoyl-2-oleoyl-3-MCPD (example of a diester):
How do 3-MCPD fatty acid esters form?
3-MCPD fatty acid esters form when oils and fats are processed at high temperatures and in the presence of chloride salts. Refinement, however, is a chemical and physical process required to maintain the quality of the oils. It is only with this thermal treatment that undesirable odourants and flavours, as well as trans fatty acids or any traces of toxic compounds, such as pesticides, heavy metals and mycotoxins, can be removed.
On the other hand, not all vegetable oils are affected in the same way. While the concentration of 3-MCPD fatty acid esters in seed oils, such as rapeseed, soy or sunflower oil, are partially below the detection limit, fruit oils, such as refined palm or olive oil, have considerably higher concentrations. Yet due to their specific properties, fruit oils cannot easily be replaced by seed oils.
What are the risks of 3-MCPD and 3-MCPD fatty acid esters?
Lab tests with animals have shown that a prolonged raised intake of free 3-MCPD can lead to the formation of benign tumors in the renal tubules. The Joint FAO/WHO Expert Committee (JECFA) and the Scientific Committee on Food (EU) therefore defined a tolerable daily intake (TDI) of 2 µg per kg of body weight for free 3-MCPD.
It is not yet clear to what extent ester-bound 3-MCPD is released by the human digestive system. Toxicological assessments are therefore based on the assumption that 3-MCPD fatty acid esters ingested with food are fully released and recommend the TDI value for free 3-MCPD. The TDI for free 3-MCPD may be significantly exceeded in foods if the bound 3-MCPD is broken down as a result of enzymatic hydrolysis in the human body.
A grown person weighing 70 kg must not ingest more than 140 µg 3-MCPD daily (2 µg x 70 kg). When consuming 50 g of chocoloate, for instance, containing a measured 3-MCPD content of 5 mg/kg, the TDI of 2 µg per kg of body weight is already heavily exceeded (50 g x 5 mg/kg = 250 µg).
Apart from the general principle of limiting contaminants to values “as low as reasonably achievable” (ALARA) through good manufacturing practice, there are currently no statutory regulations regarding contamination with 3-MCPD esters. The EU merely specifies maximum values of 50 μg/kg dry matter regarding contamination of hydrolysed plant protein and soy sauce with (free) 3-MCPD.
Analytics of 3-MCPD fatty acid esters
Analysis of the fatty acid esters is carried out according to method 9 validated by the BfR in 2009. The sample is spiked with an internal standard (5-fold deuterated 3-MCPD), the released 3-MCPD is derivatised with phenylboronic acid (PBA) and quantified with GC/MS.
Total ion chromatogram (TIC) of a grown matrix sample (3-MCPD content: 2 mg/kg fat).