EFFECT OF PH ON ANTIOXIDANT ACTIVITY OF ALPHA-TOCOPHEROL AND TROLOX IN OIL-IN-WATER EMULSIONS

The pH had a more significant effect on the antioxidant activity of Tr olox than alpha-tocopherol in corn oil emulsified with Tween 20 at 60 degrees C. Although with increasing pH the oxidative stability of corn oil emulsions decreased, the antioxidant activity of alpha-tocopherol increased. Initially, Trolox and alpha-tocopherol were similar in inh ibiting hydroperoxide formation with or without phosphate buffers at p H 3-7, but at later stages alpha-tocopherol was more effective than Tr olox at pH 3, 4, 5, and 7 but not at pH 6. In contrast, alpha-tocopher ol inhibited hexanal formation better than Trolox during the entire ox idation period. Trolox was more stable than alpha-tocopherol in bulk c orn oil but less stable in Tween 20 solutions at different pH. Both an tioxidants in Tween 20 solutions were most stable at pH 3 and least st able at pH 7. Although more Trolox partitioned into the oil phase and the oil-water interfaces at pH 3-4, its antioxidant activity was lower than at pH 5-6. The overall antioxidant activities of alpha-tocophero l and Trolox depend on their hydrogen-donating ability, relative stabi lity, and distribution in emulsions.