Glycidols Esters, 2-Chloropropane-1,3-Diols, and3-Chloropropane-1,2-Diols Contents in Real Olive Oil Samples and their Relation with Diacylglycerols

A series of authentic virgin, refined, and mix-tures of olive oils was analyzed for their content of 2-and3-chloropropanediol (MCPD) esters expressed as 2−/-3-MCPD, glycidol (and related glycidyl esters) (GE), anddiglycerides (DAG). High concentrations of MCPD andGE were found, above all, in pomace oils, which comefrom the poorer starting raw materials, while virgin oliveoils, as expected, do not contain any process contaminant.On the other hand, DAGs are present in all samples, dem-onstrating that their involvement in the formation of suchcontaminants only occurs when temperatures are higherthan that used during the refining steps. The lack of correla-tion between the amounts of MCPD and GE can beascribed to their completely different chemical stability asthe epoxy ring of the GE opens easily, leading to bothshort-chain derivatives and/or MCPD itself. Thisfindingcan also explain the data about the absence of 2-MCPD inall the analyzed oil samples: other than the statistical proba-bility and the steric effect of the SN2 formation mecha-nism, both in favor of the 3- derivative, we have also toconsider the MCPD formation pathway involving glycidolthat, under opportune conditions of refining, can increasethe whole amount of 3-MCPD (under thermodynamic con-trol, 3-MCPD is more stable).