Efficacy of myricetin as an antioxidant in methyl esters of soybean oil*

The antioxidant activity of myricetin, a natural flavonol found in fruits and vegetables, was determined in soybean oil methyl esters (SME) and compared with a-tocopherol and tert-butylhydroquinone (TBHQ) over a 90-day period employing EN 14112, acid value, and kinematic viscosity methods. Myricetin had greater antioxidant activity than a-tocopherol, but was inferior to TBHQ. Synergism was observed between myricetin and TBHQ, but antagonism between a-tocopherol and either myricetin or TBHQ was discovered. A binary mixture of myricetin and TBHQ at 1000 ppm (1:1) was the most effective treatment investigated at inhibiting oxidation of SME. Myricetin was not completely soluble in SME at 1000 ppm, suggesting that 500 ppm is a more appropriate treatment level. Pro-oxidant activity of atocopherol was observed when added to SME obtained from crude soybean oil, but antioxidant behavior was observed in distilled SME. Addition of a-tocopherol to methyl esters initially free of antioxidants revealed that 600–700 ppm was the optimum concentration for antioxidant activity. Acid value and kinematic viscosity remained within prescribed specifications after 90 days, despite failure of a number of samples with regard to EN 14112, suggesting that these parameters are insufficient as sole indicators of oxidation stability.