Abstract
The effects of phospholipids on the oxidative dimerization of dl-α-tocopherol (α-Toc) and d-δ-tocopherol (δ-Toc) during the thermal oxidation of trilaurin (Tri-La) and of trilinolein (Tri-Li) were examined. Experimental procedures were the same as those described in the previous papers of this series. α-Toc was oxidized with air at 180°C for 10h, and δ-Toc for 5h.
A little influence of phospholipids on the oxidative stability of tocopherols was observed at the oxidation in Tri-La. (Tables-1 and 2) When tocopherols were oxidized in Tri-Li, the stability of tocopherols increased greatly by the addition of small amount of phosphatidyl choline or phosphatidyl ethanolamine. (Figs.-1 and 4) Similar effect was observed at the addition of tri-n-butyl phosphate (TBP), while tri-n-octylamine (TOA) gives no influence on the oxidative dimerization of tocopherols. (Figs.-2 and 4) This phenomenon is similar to that observed at the oxidation of γ-Toc, which was shown in the Part IV of this series. This fact shows that phosphate ester linkage supresses the oxidation of tocopherols in Tri-Li. The formation of 1, 2-bis (γ-tocopherol-5-yl) ethane (α-TED) was scarcely influenced by the addition of phospholipids, TBP and TOA. (Fig.-3) On the other hand, the amount of 5- (δ-tocopheroxy) -δ-tocopherol (δ-TED) formed from δ-Toc decreased remarkably;but the amounts of 5- (δ-tocopherol-5-yl) -δ-tocopherol and its atropisomer [δ-TBD (H) and δ-TBD (L)] were slightly influenced by the addition of phospholipids or TBP in Tri-Li. (Figs.-5, 6 and 7)
