Esters of 3-chloro-1,2-propanediol (3-MCPD) in vegetable oils: significance in the formation of 3-MCPD.

3-Mono-chloropropane-1,2-diol (3-MCPD) is a contaminant that occurs in food in its free (diol) form as well as in an esterified (with fatty acids) form. Using a simple intestinal model, it was demonstrated that 3-MCPD monoesters and 3-MCPD diesters are accepted by intestinal lipase as substrates in vitro. Under the chosen conditions, the yield of 3-MCPD from a 3-MCPD monoester was greater than 95% in approximately 1 min. Release from the diesters was slower, reaching about 45, 65 and 95% of 3-MCPD after 1, 5 and 90 min of incubation, respectively. However, in human, the hydrolysis of 3-MCPD esters is unlikely to release 100% as 3-MCPD, as triglycerides and phospholipids are hydrolysed in the intestine liberating 2-monoglycerides. Assuming a similar metabolism for 3-MCPD esters as that known for acylglycerols in humans in vivo, the de-esterification in positions 1 and 3 would thus be favoured by pancreatic lipases. Therefore, 3-MCPD, and 3-MCPD-2 monoesters would be released, respectively, from the 1-/3-monoesters, and the diesters potentially present in food. Hence, information on the exact amounts of the partial fatty acid chloroesters, i.e. 3-MCPD mono- and diesters, is important to assess the contribution of foods to the bioavailability of 3-MCPD. Therefore, a rapid method for the determination of the ratio of 3-MCPD monoesters to diesters in fats and oils was developed using gas chromatography-mass spectrometry (GC-MS) and isotopically labelled 3-MCPD esters as internal standards. The analysis of 11 different samples of fat mixes typically employed in food manufacturing demonstrated that a maximum of about 15% of the total amount of 3-MCPD bound in esters is present in the monoesterified form. The potentially slower release of 3-MCPD from 3-MCPD diesters, and the mono- to diesters ratio suggest that 3-MCPD esters may in fact contribute only marginally to the overall dietary exposure to 3-MCPD. Further work on the bioavailability, metabolism and possible toxicity of chloroesters per se is warranted.