Submitted to: European Journal of Lipid Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2008
Publication Date: 9/1/2008
Citation: Moser, B.R. 2008. Efficacy of Myricetin as an Antioxidant in Methyl Esters of Soybean Oil. European Journal of Lipid Science and Technology. 110:1167-1174. Interpretive Summary: Biodiesel derived from soybean oil suffers from poor oxidative stability in comparison to conventional petroleum diesel fuel. Oxidative degradation of biodiesel, which commonly occurs during storage, negatively impacts important fuel properties. As a result, biodiesel which has undergone unwanted oxidative degradation no longer satisfies relevant legal fuel quality standards. Therefore, antioxidant additives are commonly added to biodiesel to prevent or delay oxidative deterioration of the fuel during storage. These additives are normally synthetic and non-biodegradable, and are often derived from petrochemical feedstocks. The objective of this study was to evaluate the effectiveness of a bio-degradable antioxidant obtained from a natural source at preventing or delaying oxidative degradation of biodiesel. This antioxidant, a flavonoid, is called myricetin and is found in a number of common fruits, vegetables, leaves, and flowers. When added to biodiesel, it significantly improved the storage stability by preventing unwanted oxidative degradation of the fuel. This result is important because it demonstrates the effectiveness of certain natural antioxidants as additives in biodiesel, thus displacing materials potentially derived from petrochemical feedstocks. Preventing or delaying oxidative degradation of biodiesel is also very important because biodiesel of poor quality may erode public confidence in alternative fuels and complicate our Nation’s goal of reduced dependence on imported petroleum fuels.
Technical Abstract: 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 alpha-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 d, despite failure of a number of samples with regard to EN 14112, suggesting that these parameters are insufficient as sole indicators of oxidation stability.