Effects of alpha-, gamma-, and delta-tocopherols on the autoxidation of purified rapeseed oil triacylglycerols in a system containing low oxygen.
Controversial data on the antioxidant effects of tocopherols have already been shown in different test systems, yet delta-tocopherol was hardly considered. This study was designed to assess the effects and degradation of alpha-, gamma-, and delta-tocopherol in four concentrations from between 0.01 and 0.25% on the oxidation of purified rapeseed oil trigacylglycerols (RO-TAG) at 40 degrees C in the dark in a low oxygen containing system for 11 weeks. Oxidation experiments were performed weekly by assessing primary (peroxide value, PV; conjugated dienes, CD) and secondary (p-anisidine reactive products, p-AV; hexanal) oxidation products, the degree of unsaturation with the iodine value (IV), and the stability of tocopherols. Test approaches were performed with and without the addition of 0.01% alpha,alpha'-azoisobutyronitrile (AIBN), which is a known radical initiator. alpha- and gamma-Tocopherols increased the rate of lipid oxidation, which was more pronounced in the presence of AIBN. Only the lowest amount of 0.01% gamma-tocopherol was comparable to the control sample in the test without AIBN. The most effective was shown to be delta-tocopherol, which did not elevate lipid oxidation except the PV in the AIBN test, but they did not delay it either. delta-Tocopherol was the most stable followed by gamma- and alpha-tocopherol. For alpha- and gamma-tocopherol, but not for delta-tocopherol, strong correlations were found between the tocopherol degradation and the extent of oxidation. Results suggest that (i). at concentrations higher than 0.05%, tocopherols are less efficient and turn their mode of action or participate in side reactions in RO-TAG and (ii). delta-tocopherol was shown to be the most stable and effective under these low oxygen conditions.
Isnardy
Bettina
B
Institute of Nutritional Sciences, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria.
Wagner
Karl-Heinz
KH
Elmadfa
Ibrahim
I
D000975:Antioxidants / Q000494:pharmacology; D004355:Drug Stability; D005229:Fatty Acids, Monounsaturated; D015227:Lipid Peroxidation / Q000187:drug effects*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000032:analysis; D010938:Plant Oils / Q000737:chemistry*; D000074262:Rapeseed Oil; D024505:Tocopherols / Q000494:pharmacology*; D014280:Triglycerides / Q000737:chemistry*; D024502:alpha-Tocopherol / Q000494:pharmacology*; D024504:gamma-Tocopherol / Q000494:pharmacology*
D000975:Antioxidants; D005229:Fatty Acids, Monounsaturated; D010938:Plant Oils; D000074262:Rapeseed Oil; D014280:Triglycerides; D024504:gamma-Tocopherol; D024502:alpha-Tocopherol; C479072:delta-tocopherol; D024505:Tocopherols; D010100:Oxygen