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Methods to determine the chain-breaking AOA of food

Methods to determine the chain-breaking AOA of food. Jessica Hudson. Chain-breaking antioxidant activity. Purpose: to take the free radicals out of the reaction to prevent them from being involved in propagation

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Methods to determine the chain-breaking AOA of food

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  1. Methods to determine the chain-breaking AOA of food Jessica Hudson

  2. Chain-breaking antioxidant activity • Purpose: to take the free radicals out of the reaction to prevent them from being involved in propagation • Ex.: Beta-Carotene is thought to trap free radicals, so it is difficult to classify as either preventive or chain breaking

  3. Methods to determine chain-breaking AOA • Indirect: based on measurements of the inhibition of various intermediates of or final products of oxidation • Direct Competition: natural antioxidants compete for the peroxy radical with a reference free radical scavenger • Direct: free radical production and its inhibition by antioxidants is directly measured

  4. Direct Competition methods • Free-radical induced decay of fluorescence of R-phycoerythrin • Crocin bleaching • B-carotene bleaching • Competition between antioxidant and KI for the peroxyl radical

  5. Free-radical induced decay of fluorescence of R-phycoerythrin • PE is applied as a reference scavenger • Principle: intensity of PE decreases in the presence of peroxyl radical, but in presence of chain-breaking antioxidant this decay is slowed down

  6. Crocin bleaching • Crocin (a natural compound) undergoes bleaching in the presence of peroxyl radicals • The addition of a sample containing antioxidants results in a decreased rate of crocin decay • Originally designated for testing blood plasma

  7. Chain-breaking activity of roasted coffee • In this experiment, the crocin bleaching method was used to determine the chain-breaking activity of the roasted brews. • This procedure measures the ability of a compound or mixture of compounds to quench peroxyl radicals. • This bleaching occurs in the presence of peroxyl radicals, and is slowed in the presence of an antioxidant. • It was found that MRPs (Maillard reaction products) have significant chain-breaking antioxidant activity.

  8. B-carotene bleaching • Bleaching of B-carotene occurs during the autooxidation of linoleic acid • Addition of antioxidant containing sample retards B-carotene decay

  9. Indirect methods • ABTS test • DPPH test • Reduction of the Fremy’s radical • Etc.

  10. ABTS test • One of the most popular indirect assays • Principle: to monitor the decay of radical cation ABTS produced by the oxidation of 2,2’-azinobis(3-ethylbenzothiaziline-6-sulfonate) caused by the addition of a phenolic-containing sample

  11. TEAC assay • Based on the inhibition of the absorbance of ABTS (2,2’-azinobis(3-ethylbenzothiazoline 6-sulfonate)) by antioxidants • ABTS radical is very stable on its own, however will rapidly react with a phenolic (which is an H-atom donor). • Advantages: simple and easy to use in different laboratories

  12. DPPH test • Measures how 2,2-diphenyl-1-picrylhydrazyl (stable radical) reacts with an H-donor such as a phenolic • DPPH does not react with flavonoids • There are two types of this reaction: dynamic and static

  13. Reduction of the Fremy’s radical • Capability of potassium nitrosidsulfonate to react with H-donors • Specifically used for wine testing

  14. Catechins and catechin-gallate esters in green and black tea • One objective of this study was to determine the relative antioxidant potentials of catechins and catchin-gallate esters. • In this study, the oxidation of low-density lipoproteins modeled the efficacy of the different polyphenols as chain-breaking antioxidants. • In this model, copper ion catalysts were left out of the solution to avoid the polyphenols acting as metal chelators. • Chain-breaking antioxidants intercepted peroxidation process by reducing peroxyl radicals to alkoxides or hydroperoxides.

  15. What is the relative effectiveness of these catechin-gallate esters? • Gallic acid is the least effective, followed by EGC and catechin. • ECG, EGCG, and EC tended to have similar effectiveness. • Concluded that gallic acid is a more effective scavenger in the aqueous phase whereas epicatechin and catechin are better antioxidants against lipid peroxyl radicals.

  16. References • Hamilton, R.; Kalu, C.; Prisk, E.; Padley, F.; Pierce, H. Chemistry of free radicals in lipids. Food Chemistry. 1997, 60, 193-199. • Nicoli, M.; Anese, M.; Manzocco, L.; Lerici, C. Antioxidant properties of coffee brews in relation to the roasting degree. LWT Food Science and Technology. 1997, 30, 292-297. • Rice-Evans, C. Plant polyphenols: free radical scavengers or chain-breaking antioxidants? Biochemical Society Symposia. 1995, 61, 103-116. • Roginsky, V.; Lissi, E. Review of methods to determine chain-breaking antioxidant activity in food. Food Chemistry. 2004, 92, 235-254. • Salah, N.; Miller, N.; Paganaga, G.; Tijburg, L; Bolwell, G.; Rice-Evans, C. Polyphenolicflavanols as scavengers of aqueous phase radicals and as chain-breaking antioxidants. Archives of biochemistry and biophysics. 1995, 322, 339-346.

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