Document Type : Full Research Paper
Authors
Department of Food Science and Technology, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran
Abstract
Introduction
Today, many edible oils such as palms, corn, soybeans and sunflowers are used in food preparation. Essential oleic, linoleic and linolenic fatty acids, found abundantly in olive, sunflower and soybean oils, respectively, play an important role in maintaining health. Antioxidant compounds are used to increase the shelf life of oils, which are classified into two groups of natural and synthetic antioxidants based on the source of production. Phenolic acids are a subset of a large group of phenolic compounds that are used as natural antioxidants in industry. Gallic acid is much stronger than protocatchuic acid due to its three hydroxyl groups. However, the presence of more than three hydroxyl groups does not seem to increase the antioxidant effect in oily systems. The position of the hydroxyl group on the aromatic ring also affects the antioxidant activity, so that the replacement of the hydroxyl group in the ortho and para position increases the antioxidant activity of phenolic acids. Methyl gallate, which is widely found in plants and polyphenolic secondary metabolites, is a natural antioxidant. Despite efforts to date, no suitable natural antioxidant has been proposed to control the thermal oxidation of oils at high temperatures. Therefore, due to the widespread use of oils in food, the thermal stability of natural antioxidants gallic acid and methyl-gallate compared to the powerful but synthetic antioxidant TBHQ, depending on the degree of satiety of the lipid system (sunflower oil and olive oil) and 80 degrees Celsius will be evaluated in this study.
Material and Methods
Samples of sunflower and olive oil were purchased from local stores. All chemicals and solvents were provided by Merck and Charlot. Sunflower and olive oil were purified by column chromatography to remove natural antioxidants. Oxidation of purified sunflower oil (1 g per oil) in the presence of a concentration level of gallic acid, methyl gallate and TBHQ (1.2 μmol / g) in glass bottles. The rate of progression of oxidative reactions and the evaluation of oil quality during temperature application is possible by measuring the peroxide number. The carbonyl number is determined using 2-propanol as solvent and 2,4 decodenal as standard and absorbance at 420 nm. The effect of antioxidants (InH) on the oxidation of the test samples can be measured based on the kinetic parameters. These parameters are stability factor F, ORR oxidation rate ratio, activity A and average consumption of WInH antioxidants.
Results and Discussion
The minimum and maximum induction times are related to the control sample and the sample containing the synthetic antioxidant TBHQ, respectively, which, considering the position of the two hydroxyl groups in the para position relative to each other in the TBHQ molecule, make this antioxidant stronger. Justifies. At 80 ° C and in sunflower oil, the antioxidant methyl gallate shows a more effective stability factor (F) and antioxidant activity (A), indicating greater antioxidant power than gallic acid. Similarly, F-ORR-A values in methylgalate treatment have a significant effectiveness compared to other treatments. The higher oxidative stability of olive oil against sunflower oils can be attributed to the small amounts of oleic acid and especially the small amounts of linolenic acid in olives. Stability factor (F), is significantly higher for the TBHQ antioxidant than the values obtained for the other two. This factor is affected by the induction period of antioxidants and can be expected due to the effectiveness of antioxidants in increasing the duration of the induction period. The highest value obtained for the ORR oxidation rate parameter, is related to the antioxidant gallic acid. The parameter of antioxidant activity A, in TBHQ is higher than the other two antioxidants. Measurement of carbonyl compounds resulting from the decomposition of hydroperoxides is a good measure of the rate of development of oxidative reactions. In the treatment of gallic acid and TBHQ, the changes in the carbonyl number decrease at the end of the annealing, which is probably due to the decomposition of carbonyl compounds and the production of polymer compounds. Which cannot be measured by carbonyl number test.
Conclusion
Better efficacy of gallic acid compared to methyl gallate in olive oil and better efficacy of methyl gallate compared to gallic acid in sunflower oil at 80 ° C show the composition of fatty acids, the nature of lipid systems and the position of antioxidants in the reaction medium. , Have a great effect on improving the performance of antioxidants. Determination of oxidative stability based on carbonyl number shows similar results to peroxide number .
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