The effects of alpha- and delta-tocopherol on inhibition of hydroperoxides, keto and hydroxy compounds at Rancimat conditions, i.e. 100 ºC and air bubbling, were studied in samples of fatty acid methyl esters (FAME) obtained from high linoleic (HL) and high oleic (HO) sunflower oils. Simple hydroperoxides from methyl linoleate and oleate and keto and hydroxy compounds derived from methyl linoleate hydroperoxides were analyzed by HPLC-UV-ELS. Different tocopherol concentrations, namely, 10, 50, 100, 500 and 1000 mg/kg, were tested. Irrespective of the lipid substrate and the initial concentration of tocopherol, results showed that the content of hydroperoxides accumulated during the induction period was remarkably higher in the samples containing delta-tocopherol. The relative concentrations of oleate hydroperoxides in the HO samples were also higher in the presence of delta-tocopherol. Alpha-tocopherol was more effective in inhibiting hydroperoxides at low levels, being 100 mg/kg its optimal concentration, while delta-tocopherol displayed optimal protection at 1000 mg/kg. Under the oxidation conditions applied, neither alpha- nor delta-tocopherol showed a protective effect on hydroperoxide decomposition at any level assayed. Formation of keto- and hydroxy-dienes was more related to the concentration of their hydroperoxide precursors. Furthermore, both tocopherols gave rise to increased concentrations of ketodienes at 500 and 1000 mg/kg compared to the controls. Such an effect was more pronounced for alpha-tocopherol and in the HL samples.

This work was Funded by the Spanish Ministry of Economy and Competitiveness through project AGL2013-45110-R and CSIC through a PIE project with reference 201270E134. The authors also thank the Spanish Ministry of Economy and Competitiveness for supporting Susana Marmesat with a “Juan de la Cierva” contract with reference JCI-2011-08874.

Peer Reviewed