Effects of tocopherols and tocotrienols on the inhibition of autoxidation of conjugated linoleic acid

HPLC Separation of Vitamin E and Its Oxidation Products and Effects of Oxidized Tocotrienols on the Viability of MCF-7 Breast Cancer Cells in Vitro

Tocotrienols, a vitamin E subgroup, exert potent anticancer effects, but easily degrade due to oxidation. Eight vitamin E reference compounds, α-, β-, γ-, or δ-tocopherols or -tocotrienols, were thermally oxidized in n-hexane. The corresponding predominantly dimeric oxidation products were separated from the parent compounds by diol-modified normal-phase HPLC-UV and characterized by mass spectroscopy. The composition of test compounds, that is, α-tocotrienol, γ-tocotrienol, or palm tocotrienol-rich fraction (TRF), before and after thermal oxidation was determined by HPLC-DAD, and MCF-7 cells were treated with both nonoxidized and oxidized test compounds for 72 h. Whereas all nonoxidized test compounds (0-100 μM) led to dose-dependent decreases in cell viability, equimolar oxidized α-tocotrienol had a weaker effect, and oxidized TRF had no such effect. However, the IC50 value of oxidized γ-tocotrienol was lower (85 μM) than that of nonoxidized γ-tocotrienol (134 μM), thereby suggesting that γ-tocotrienol oxidation products are able to reduce tumor cell viability in vitro.

Effectiveness of α-, γ- and δ-Tocopherol in a CLA-Rich Oil

Conjugated linoleic acid (CLA) is a mixture of positional and geometric isomers of octadecadienoic acid with conjugated double bounds. Positive health properties have been attributed to some isomers, such as anticarcinogenic activity, antiartherosclerotic effects and reduction of body fat gain. Hence, oils rich in CLA such as Tonalin^® oil (TO), normally obtained through alkaline isomerization of safflower oil (SO), an oil rich in linoleic acid (LA), are currently used in functional foods. However, special care must be taken to protect them from oxidation to ensure the quality of the supplemented foods. The objective of this work was to evaluate the oxidation and effectiveness of different tocopherol homologues (α-, γ- and δ-), alone or in combination with synergists (ascorbyl palmitate and lecithin), in TO compared to SO at different conditions, ambient temperature (25 °C) and accelerated conditions in Rancimat (100 °C). The oils, the oils devoid of their antioxidants and the latter containing the antioxidants added were assayed. Results showed great differences between SO and TO in terms of formation of hydroperoxides and polymers and also in the effectiveness of tocopherols to delay oxidation. TO showed higher levels of polymerization and, in general, the effectiveness of tocopherol homologues, alone or in combination with synergists, was also lower in the TO.

Identification of α-tocotrienolquinone epoxides and development of an efficient molecular distillation procedure for quantitation of α-tocotrienol oxidation products in food matrices by high-performance liquid chromatography with diode array and fluorescence detection

The aim of this study was to investigate the most important oxidation products of α-tocotrienol (α-T3) along with other tocochromanols in lipid matrices and tocotrienol-rich foods. For this purpose, an efficient molecular distillation procedure was developed for the extraction of analytes, and α-T3-spiked and thermally oxidized natural lipids (lard and wheat germ oil) and α-T3-rich foods (wholemeal rye bread and oil from dried brewer's spent grain) were investigated through HPLC-DAD-F. The following α-T3 oxidation products were extractable from lipid matrices along with tocochromanols: α-tocotrienolquinone (α-T3Q), α-tocotrienolquinone-4a,5-epoxide (α-T3Q-4a,5-E), α-tocotrienolquinone-7,8-epoxide (α-T3Q-7,8-E), 7-formyl-β-tocotrienol (7-FβT3), and 5-formyl-γ-tocotrienol (5-FγT3). Recovery rates were as high as 88% and enrichment factors up to 124. The proposed method allows the investigation of α-T3Q, α-T3Q-4a,5-E, α-T3Q-7,8-E, 7-FβT3, and 5-FγT3 in small quantities (<0.78 μg/g) in lipid matrices, which is necessary for the investigation and analysis of the formation kinetics of these oxidation products in fat, oils, and tocotrienol-rich foods.

Effect of antioxidants on soy oil conjugated linoleic acid production and its oxidative stability

Conjugated linoleic acid (CLA)-rich soy oil can be produced by photoisomerization of soy oil linoleic acid to produce a soy oil with up to 20% CLA. Recent studies indicate that mixed soy tocopherols added to refined bleached deodorized (RBD) oil produced significant increase in soy CLA yield during soy oil linoleic acid photoisomerization. However, the effect of common synthetic free radical scavenging antioxidants and specific tocopherols on CLA yield and its oxidative stability is not known. Therefore, this investigation evaluated the effects of various antioxidant systems on soy oil CLA yield and oxidative stability. Soy oil with added antioxidants consisting of combinations of mixed tocopherols (MT), ascorbyl palmitate (AP), butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and tert-butylhydroquinone (TBHQ) was photoisomerized to produce CLA- rich soy oil. The CLA content was determined by GC-FID analysis and oxidative stability by peroxide value (PV). The soy oil in the presence of TBHQ, MT alone and MT with 500 ppm of AP produced significantly greater CLA yields and improved oxidative stability compared to a control without added antioxidants (p < 0.05). However, added mixed tocopherols produced the greatest CLA yield and also reduced PV relative to the control. Tocopherols in the form of α-, γ- and δ-tocopherols were then each examined as to their relative effect on CLA yields and PV. The largest increase in CLA yield was obtained with 1800 ppm of γ-tocopherols with reduced PV. Mixed tocopherols, TBHQ and γ-tocopherols can be used to increase CLA yield and reduce PV of soy oil during linoleic acid photoisomerization.