Behavior of phenolic antioxidants in a partitioned medium: Structure-activity relationship

The behavior of phenolic antioxidants is studied in a partitioned medium, composed of linoleic acid dispersed in an aqueous phase. Their efficiency is measured by the diene production during oxidation, induced by Fe (II)/ascorbic acid at 30 degrees C. With a linoleic acid/Fe2+ molar ratio of 10 and a Fe2+/ascorbic acid molar ratio of 23, a steady-state propagation rate is reached after 1 h for up to 15 h. The antioxidants cannot avoid the early dienes (30-40% of total dienes), resulting from the inducing reactions; however, they can stop all the dienes produced during propagation reactions by acting on ROO.. The inhibition values reveal a great difference between the antioxidants, depending on their structure (number of hydroxyl groups or chelating sites) and on their polarity, confirming the "polar paradox." Thus, a-tocopherol, butylated hydroxytoluene, butylated hydroxyanisole, and isoeugenol appear to be the best antioxidants, but rosmarinic and caffeic acids, generally potent antioxidants, present a weak efficiency. Surprisingly, in such a metal-induced system, the chelator activity seems to play a minor role.