1 / 16

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

alexander-woodard
Download Presentation

Methods to determine the chain-breaking AOA of food

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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.

More Related