Add time:07/24/2019         Source:sciencedirect.com

The autoxidation of fatty acid methyl esters (FAMEs) derived from colza, sunflower, linseed and tung oils and the oxidation of sunflower FAMEs in the presence of several commercial driers based on Co(II), Mn(II), Fe(II), V(IV), Sr(II), Zr(IV), Ca(II), Zn(II) have been investigated. The oxidation step was studied through oxygen uptake measurements with an automatic O2 pressure recorder (RapidOxy®) and by ATR-FTIR spectroscopy. Pure methyl linoleate hydroperoxides (ROOH) were prepared by photooxidation to follow their decomposition by HPLC in the presence of the driers. Only Co(II), Mn(II) and Fe(II) as primary driers have catalytic effects both on the oxidation and on the ROOH decomposition steps. However, the Co-based drier shows the higher oxidation rate while the Fe-based drier has the greater ROOH decomposition rate. On the other hand, oxidation runs faster by increasing the amount of driers from 2.5 to 25–50 mM but an antioxidant behavior is observed at higher levels. Secondary driers show poor or no catalytic activities both on the oxidation and the ROOH decomposition steps with a conversion ranging from 5 to 9% over 24 h. Combinations of driers were finally investigated to highlight possible synergistic or antagonist effects during the oxidation and hydroperoxides decomposition steps. Synergistic effects were found only on the oxidation stage with Co(II)-Zn(II), Mn(II)-Zn(II) and Fe(II)-Ca(II), while these latter do not have influence on the decomposition step.

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