Formation Mechanism Of3-monochloro-1,2-propanediol (3-MCPD) Fatty Acid Esters In Refined Edible Oils

3-chloro-1,2-propanediol (3-MCPD) fatty acid esters, a well-knownprocess-induced food contaminant with nephrotoxicity and carcinogenicpotential, have been detected in many food products, including bread,coffee, refined vegetable oils, infant formula, salty crackers, dark malt,French fries, doughnuts, pickled olives and herrings. The detection of3-MCPD esters in human breast milk in2008indicated that3-MCPDesters might be absorbed and distributed in human tissues and organs. Thusit has raised a food safety concern. However, the exact molecularformation mechanism of3-MCPD esters is still debating although themajority of3-MCPD esters has been proven to be generated during oildeodorization. The goal of this research was to find the formationmechanism of3-MCPD esters from diacylglycerol (DAG) andtriacylglycerol (TAG) while enhancing food safety and agricultureeconomy. The specific objectives were:1) To test the hypothesis that free radical was formed and mediatedthe formation of3-MCPD fatty acid diesters taken DAG asprecursors.2) To investigate the formation mechanism of3-MCPD esters fromTAG.Our first study was conducted to test whether free radicals areformed and served as intermediates for3-MCPD diester formation at hightemperature under a low-moisture condition, similar to that during the oilrefining process. First, the presence of free radicals in a vegetable oil keptat120°C for20min was demonstrated using an electron spin resonance (ESR) spectroscopy examination with5,5-dimethylpyrroline-N-oxide(DMPO) as the spin trap agent. ESR investigation also showed anassociation between thermal treatment degree and the concentration of freeradicals. A Fourier transform infrared spectroscopy (FT-IR) analysis ofsn-1,2-steareoglycerol (DSG) at25°C and120°C suggested a possibleinvolvement of ester carbonyl group in forming3-MCPD diesters. Basedon these results, a novel free radical mediated chemical mechanism,including the formation of an intermediate CAFR followed by anucleophilic substitution with chlorine radicals, was proposed for3-MCPDdiester formation. Furthermore, a quadrupole-time of flight (Q-TOF)MS/MS investigation was performed and detected the DMPO adducts withthe cyclic acyloxonium free radicals (CAFR) and its product MS ions,approving the presence of CAFR. Furthermore, the free radical mechanismwas validated by the formation of3-MCPD diesters through reacting DSGwith a number of inorganic and organic chlorine sources including chlorinegas at120°C and240°C. Findings of this study might lead to improve oiland food processing conditions to reduce the level of3-MCPD diesters infoods and enhance food safety.Our second research was to investigate the formation mechanism of3-MCPD esters from TAG, the major acylglycerol class in refined oils,especially accounting for as high as88-96%of total glycerides in palm oils.To clarify this mechanism is incredibly important to find solutions ofreducing3-MCPD esters’ level in refined oils. First, a series of modelreaction mimicking oil deodorization has been conducted with puretristearoylglycerol (TSG) in the presence of different chlorine containingcompounds including both organic and inorganic chloride. Anultra-performance liquid chromatograph (UPLC) Q-TOF MS analysis ofthe reaction products showed that only FeCl2and FeCl3at120°C and240°C, HCl gas at240°C resulted in the formation of3-MCPD diesters,suggesting the formation mechanism of3-MCPD esters from TAG mightdifferent with that from DAG. In addition,3-MCPD mono-ester was also detected in the reaction product of FeCl3and TSG at both120°C and240°C, suggesting that TAG also might be3-MCPD mono-esterprecursors. Second, the generation of3-MCPD esters through the additionof FeSO3+4or Fe2(SO4)3to the model reaction indicated that Feand Fe2+could somehow catalyze the formation of3-MCPD mono-esters and mightplay a very important role to form3-MCPD mono-esters during oildeodorization. Then ESR and FT-IR were used to determine the reactionintermediate structure. ESR determination of the mixture of TSG,Fe2(SO4)3and DMPO revealed the generation of free radicals, while FT-IRanalysis of TSG at25and120°C indicated the hydrolysis of the estercarbonyl groups at high temperature. Based on these data, three possiblepathways, including the hydrolysis of TAGs, followed by the formation ofcyclic acyloxonium ion, glycidol esters or cyclic acyloxonium free radicalintermediates, were proposed. The hypothesis also suggested that thegeneration of3-MCPD ester might highly associate with the lipidoxidation during oil deodorization.Taken together, results from this research demonstrate that possibleformation mechanism of3-MCPD esters from both DAG and TAG. Theresults might provide important scientific insight for reducing the level of3-MCPD esters in refined edible oils while enhancing food safety andbringing in enormous profits.