Synergistic effect of lecithins for tocopherols: formation and antioxidant effect of the phosphatidylethanolamine-L-ascorbic acid condensate

Ternary mixtures of lecithins, vitamin C and vitamin E are powerful antioxidants for the stabilization of polyunsaturated (n-3 fatty acid) oils. In this study, the chemistry of the antioxidant synergistic effect was investigated in ethyl linoleate (EL) containing a-tocopherol (alpha-Toc) or in linoleate rich vegetable oils at 110 degrees C using mixtures of phosphatidylethanolamine (PE) and either l-ascorbic acid (AA) or L-dehydroascorbic acid (DHA). The highest stabilization effects in EL were similar in both systems and were found in the molar mixtures of PE and AA or DHA. The thermal formation of reaction products between PE and AA (PE-AA) or DHA (PE-DHA) were investigated by HPTLC/ESI-MS. When alpha-tocopherylquinone (alpha-TQ) was used instead of alpha-Toc, nearly the same antioxidant effect was observed in the EL system. It was shown that molar mixtures of PE and AA, or PE and DHA, can regenerate alpha-TQ to alpha-Toc at elevated temperatures. PE-AA was synthesized and tested as antioxidants in EL containing alpha-Toc and in vegetable oils at room temperature. An improved stabilization was observed with the synthesized derivative compared to the physical mixture of the compounds, which demonstrated that PE-AA is a potential new antioxidant. A mechanism for the synergistic action between PE, AA and alpha-Toc through an acid-catalysed regeneration of alpha-TQ is suggested. PE-AA is an active apolar antioxidant, which is involved in the reduction of alpha-TQ.