Study of Antioxidant Activity of Caffeic Acid and Two Caffeic Acid Esters in Bulk Oil and Oil-Water Emulsion Systems.
Ascherman, Erin M.
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William Porter has pointed out that hydrophilic antioxidants tend to be more effective in bulk oil systems and lipophilic antioxidants tend to be more effective in oil-water emulsions, this is called the Polar Paradox. Edwin Frankel explains this paradox on the basis of an antioxidant's ability to move to an oil-air or oil-water interface. He has done many experiments comparing carnosic acid, carnosol, and rosmarinic acid in bulk oil and oilwater emulsion systems. In this study compounds were prepared that have much more closely related antioxidant structures and differ primarily in their hydrophilicity. The compounds prepared were the methyl ester and octyl ester of caffeic acid. The methyl ester is more hydrophilic and the octyl ester is more lipophilic. The antioxidant effectiveness of the compounds were evaluated in bulk oil and oil-water emulsions using conjugated diene hydroperoxide values and headspace GC hexanal analysis. It was found that the results of this study tended to support the "Polar Paradox" suggested by Porter.