A kinetic study on the formation of hydroperoxy-, keto- and hydroxy-dienes in FAMEs derived from sunflower oils
The main objective of this work was to study the kinetic of formation of the main oxidation products of linoleic acid ¿hydroperoxy-, keto- and hydroxy-dienes¿ in fatty acid methyl esters (FAMEs) obtained from high-linoleic (HL) and high-oleic (HO) sunflower oils. The influence of temperature (40, 60 and 80ºC) and the addition of alpha-tocopherol (0, 500 mg/kg) on the formation of these compounds were studied. Quantitative analysis of hydroperoxy-, keto- and hydroxy-dienes was carried out by HPLC-UV. In addition, the peroxide value (PV) by iodometric titration and, when indicated, the content of alpha-tocopherol by HPLC-FLD were also determined. Monomolecular rate constants found for hydroperoxydienes ranged from 1¿10-3 to 27¿10-3 mol1/2mol-1/2h-1, while bimolecular rate constants ranged from 0.02 to 0.9 h-1 in the range of temperatures studied. The relationship between hydroperoxydienes and the PV was linear and unaffected by temperature. Results indicated that hydroperoxydienes constituted approximately 90 and 50% of total hydroperoxides in HL and HO samples, respectively. Overall formation of keto- and hydroxy-dienes was more determined by the content of their precursor hydroperoxydienes than by the oxidation temperature, as similar amounts were found for a given content of hydroperoxydienes irrespective of the temperature assayed. Addition of alpha-tocopherol had an impact on the formation of these compounds. The oxidation of oleic acid was less significant in the HO sample in the presence of the antioxidant. In this respect, hydroperoxydienes constituted approximately 75% of total hydroperoxides when the HO sample containing alpha-tocopherol was heated at 80ºC, while approximately 50% was found in the control. Therefore, alpha-tocopherol inhibited the oxidation of oleic acid to a greater extent than that of linoleic acid. In the presence of alpha-tocopherol, higher contents of keto- and hydroxy-dienes were found for a given amount of hydroperoxydienes, indicating that alpha-tocopherol may participate in the decomposition of hydroperoxides as a side reaction.
| Main Authors: | , , , |
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| Format: | comunicación de congreso biblioteca |
| Published: |
2011-09-19
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| Online Access: | http://hdl.handle.net/10261/111739 |
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