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 alpha-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 alpha-tocopherol, but was inferior to TBHQ. Synergism was observed between myricetin and TBHQ but antagonism between alpha-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 alpha-tocopherol 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.