Antioxidant Activity of Phenolic Compounds in Bulk Camellia Oil and Corresponding Oil in Water (O/W) Emulsions

The antioxidant activities of gallic acid, propyl gallate, (+)-catechin and quercetin in bulk camellia oil and corresponding emulsions were investigated using hydroperoxides and nonanal as indicators of oxidation. In bulk oil, these phenolic compounds showed antioxidant activities with the order of gallic acid>quercetin>propyl gallate> (+)catechin when measured using hydroperoxides and gallic acid>quercetin>(+)-catechin>propyl gallate using nonanal. In emulsions, propyl gallate and (+)-catechin showed antioxidant activities for the entire duration of the experiment, while quercetin and gallic acid displayed antioxidant activities for 10 days, and then pro-oxidant activities thereafter. Results suggested that in bulk oil, the antioxidant activity was regulated by phenol polarity and hydrogen atom donating ability too. In emulsions, the antioxidant activity of phenolic compounds seems to be related to their affinity toward the emulsifing agent rather than their polarity.