Antioxidant activity of gallic acid and methyl gallate in triacylglycerols of Kilka fish oil and its oil-in-water emulsion

The anti-DPPH radical effect as well as anti-peroxide activity of gallic acid, methyl gallate, and α-tocopherol in a bulk Kilka fish oil and its oil-in-water emulsion stabilized by soy protein isolate at 55 °C were investigated. Gallic acid with the lowest hydrophobicity (log P = −0.28) was found to be the most active antiradical agent (IC50 = 29.5 μM), followed by methyl gallate (IC50 = 38.0 μM, log P = −0.23) and α-tocopherol (IC50 = 105.3 μM, log P = 0.70). The anti-peroxide activity in the bulk oil system decreased in the order of methyl gallate > gallic acid > α-tocopherol. In the emulsion system, methyl gallate still behaved better than gallic acid, but the highest activity belonged to α-tocopherol. Based on the calculation of a number of kinetic parameters, the antioxidants, in general, showed better performances in the bulk oil system than in the emulsion system.