Formation of 3‑Monochloro-1,2-propanediol (3-MCPD) Di- and Monoesters from Tristearoylglycerol (TSG) and the Potential Catalytic Effect of Fe²⁺ and Fe³⁺

This study investigated whether and how triacylglycerol (TAG) may serve as a precursor for 3-monochloro-1,2-propanediol (3-MCPD) fatty acid ester formation using tristearoylglycerol (TSG). TSG was reacted with inorganic chloride compounds including NaCl, KCl, FeCl₂, CuCl_2, ZnCl₂, FeCl₃ and dry HCl, or organic chlorine compound lindane at different temperatures. Only FeCl₂ and FeCl₃ were able to form 3-MCPD esters from TSG. Further electron spin resonance (ESR) determination of TSG, Fe₂(SO₄)₃ and 5,5-dimethylpyrroline-N-oxide (DMPO) reactions revealed potential of Fe ion in promoting free radical generations under the experimental conditions. To further confirm the effect of Fe ion, chelating agent (EDTA-2Na) was added to the model reactions. The results showed for the first time that EDTA-2Na was able to reduce the generation of 3-MCPD esters. In addition, FT-IR examination indicated a possible involvement of a carbonyl group during the reaction. Taking all the observations together, the possible mechanisms, involving the formation of either a cyclic acyloxonium or a glycidol ester radical intermediate, were proposed for generating 3-MCPD fatty acid di- and mono- esters from TAG under a high temperature and low moisture condition, as well as the coformation of glycidol esters. The results from this study may be useful for reducing the level of 3-MCPD esters and related toxicants in the refined edible oils and food products.