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Detecting adul­ter­ation of extra vir­gin olive oil by dilu­tion with refined oils is chal­leng­ing because test­ing often reveals the pres­ence of com­pounds nat­u­rally present in both oils.

A recent study by sci­en­tists at Wagneningen University and Research, Netherlands, focused on deter­min­ing the pres­ence of com­pounds that are formed in the refin­ing process and remain in fully processed olive oils and other veg­etable oils. ​“Monochloropropanediol (MCPD) esters and gly­cidyl esters (GEs) may be that kind of com­pounds, but few stud­ies have looked into these com­pounds in olive oils so far,” the authors wrote.

Previous stud­ies have shown that tem­per­a­ture, heat­ing time, pH value, mois­ture con­tent, pres­sure, and oil type pro­mote the for­ma­tion of these com­pounds. Formation of 3‑MCPD esters and GEs is asso­ci­ated with high tem­per­a­ture, a method employed in the pro­duc­tion of refined oils. Higher for­ma­tion of gly­ci­dol in refined oil may also be attrib­uted to water used in the degum­ming process. These com­pounds, formed in pro­cess­ing, are hard to remove.

In this study, oil sam­ples were tested by gas chro­matog­ra­phy tan­dem mass spec­trom­e­try (GC-MS-/MS) for the pres­ence of 2‑MCPD esters, 3‑MCPD esters, and GEs. Ninety-four sam­ples included 30 extra vir­gin olive oil (EVOO), 16 pomace oil, 18 refined olive oil, 8 cold-pressed veg­etable oil, 12 refined veg­etable oil, and 10 blends.

The con­cen­tra­tions of the three com­pounds in the cold-pressed oils (EVOO and cold-pressed veg­etable oil) were sig­nif­i­cantly lower than in pomace oil or refined olive oil. The refined veg­etable oil showed val­ues between these groups.

Researchers at Wagneningen also con­sid­ered the lev­els of these com­pounds from a health stand­point. Various stud­ies have shown their tox­i­c­ity as pos­si­bly car­cino­genic. The total daily intake for an adult per­son (60kg) of 3‑MCPD esters would the­o­ret­i­cally be reached by con­sum­ing 1845.6g (approx. 1.8 liters) of EVOO per day, 39.6g (3 table­spoons) of refined olive oil per day, or 16.9 (1 table­spoon) of pomace oil per day. In prac­tice, it’s pos­si­ble to reach these lev­els. ​“It’s obvi­ous that the refined oils in the cur­rent study may con­tribute to the daily intake of 3‑MCPD esters for users of these oils and most likely to the intake of 2‑MCPD esters and GEs as well,” the authors said.

“Cold-pressed oils showed sig­nif­i­cantly lower lev­els of MCPD esters and GEs than their refined coun­ter­parts,” the authors con­cluded. Calculations revealed that 3‑MCPD ester, 2‑MCD esters, and GEs would allow detec­tion of adul­ter­ation of EVOO with 2 per­cent, 5 per­cent and 13 to 14 per­cent refined olive oil or pomace olive oil with 95 per­cent con­fi­dence. ​“This approach appears very promis­ing and sen­si­tive to detec­tion of EVOO fraud with lower pro­cess­ing grade oils,” they said.

• Food Chemistry