Efficiency of different additives in the improvement of the oxidation stability of fatty acid methyl esters with different properties

This study evaluates six formulations in improving the oxidation sta-bility of different fatty acid methyl esters (MEs). Two MEs differed in the unsaturation levels as they were synthesized from different feedstock: a blend of soybean and sunflower oils, and waste cooking oil; they did not fulfill the requirements of the EN 14214 standard concerning their oxidation stability (approximate to 0.6 h) and some impurities. The third MEs (SoSuME-EN) were fully com-pliant with the standard. Five formulations were phenolic-based, containing single or mixed antioxidant compounds of different molecular structures; one was amine-based. Different dosages of the formulations were added to the ME samples (corresponding to the addition range 50-48300 ppm). The MEs sta-bility expressed as induction periods, IP, determined by the Rancimat method, were used for the calculation of stabilization factors, SF, indicating the effi-ciency of the applied formulation. The formulation containing 2-(1,1-dimethyl-ethyl)-1,4-benzenediol was the most efficient concerning the lowest consump-tion rate and the highest SF achieved for the low quality ME. 2,2 '-Methylene--bis-(4-methyl-6-tert-butylphenol)was linked with higher antioxidant potency than the amine-based formulation and the phenolic compounds with two bulky tert-butyl groups. Among the 4 selected phenolic additives, butylated hydroxy-toluene and 2,2 '-methylene-bis-(4-methyl-6-tert-butylphenol) had similar effi-ciency in SoSuME-EN (at approximate to 500 ppm they produced SF approximate to 2), while it took twice of this amount for mixed butylphenols to achieve the same effect.