No abstract

The effect of alpha-tocopherol (alpha-T) and quercetin on the formation of hydroperoxides of linoleic and linolenic acids during autoxidation at 60 6 1 7C was investigated. Three isomers of hydroperoxides were detected using HPLC. Of isomers of linoleic acid hydroperoxides, 13-hydroperoxy-octadecadienoic acid trans-trans (13-HPODE tt), 9-HPODE cis-trans (9-HPODE c-t) and 9-HPODE trans-trans (9-HPODE t-t) were identified, constituting 64, 19 and 17% of the total amount, respectively. For linolenic acid, the components 13-hydroperoxy-octadecatrienoic acid trans-trans (13-HPO-TE t-t), 9-HPOTE c-t and 9-HPOTE t-t contributed 7, 33 and 60% to the total, respectively. The different dominant hydroperoxide isomers detected in linoleic and linolenic acids during oxidation are related to their chemical structure and the microenvironment of emulsion droplets. The ratios between specific isomers for both fatty acid hydroperoxides did not change during oxidation with or without antioxidants. Alpha-T effectively inhibited the oxidation of fatty acids and reduced the formation of hydroperoxides. The total amount of the hydroperoxides decreased along with the increase in the concentration of alpha-T, 1-40 mM. Quercetin inhibited the oxidation of both fatty acids at similar efficiency only at 40 mM concentration. A synergistic antioxidant effect of quercetin with alpha-T in a binary system on both fatty acids was observed.

The effect of added menadione (vitamin K3) on stored corn and wheat germ oil on the dissolution and dimerization of natural tocopherols and autoxidation of triacylglycerols was investigated. Samples of corn and wheat germ oils pure and with added menadione were stored at +20 degrees C in brown and transparent glass bottles. During storage their peroxide value, changes of the content of fatty acids and dissolution of tocopherols were measured. Destruction of individual tocopherols in tested oils with menadione stored in both dark and transparent glass bottles was greater than in the oil samples without menadione. However, the degradation of individual tocopherols was different in each oil. Addition of menadione to the both oils resulted in accelerated the process of autoxidation of these oils. The corn oil stored in transparent bottles was oxidized faster than the one stored in brown bottles. The pro-oxidant activity of menadione was additionally activated by light. In contrast, in the case of germ oil, the process of autoxidation was very fast regardless of sort of container. Addition of menadione to the plant oils influenced the dissolution of natural tocopherols but did not influence the dimerization of tocopherols. As from the experiment, the addition of menadione to the oils decreased their nutritive value.

The effect of added menadione (vit. K3) to stored rapeseed and soybean oil on the dissolution and dimerization of natural tocopherols and autoxidation of triacylglycerols was studied. Commercial rapeseed and soybean oils with added menadione and pure oil were stored at +20 degrees C in brown and transparent glass bottles. During storage their peroxide value, changes of the content of fatty acids and dissolution of tocopherols were measured. Destruction of individual tocopherols in tested oils with added menadione stored in both dark and transparent glass bottles were greater than in the oil samples without menadione. However, the degradation of individual tocopherols was different in each oil. Addition of menadione to the rapeseed and soybean oils resulted in the accelerated process of autoxidation of these oils. The oxidative state of the oils was lower in the oils stored in transparent bottles than in the oils stored in brown bottles. The prooxidant activity of menadione was additionally activated by light. Menadione added to the vegetable oils influenced the dissolution of natural tocopherols as well as their dimerization. It is conduced that addition of menadione to vegetable oils decreases their nutritive value.