Oxygen Radical Absorbance Capacity

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With the help of the Oxygen Radical Absorbance Capacity ( ORAC ; dt .: ability to intercept oxygen radicals) the antioxidant capacity of a sample can be indicated. The vitamin E derivative Trolox serves as a reference for the measurement , which is why the result is given in Trolox equivalents. The ORAC value is often determined for food.

The ORAC measurement is applicable to water-soluble (ORAC or H-ORAC) and fat-soluble antioxidants (L-ORAC). In comparison with other methods for determining the antioxidant capacity (e.g. TEAC , FRAP ), the ORAC measurement observes the antioxidant reaction during its entire course and not just measured it at a specific point in time.

Measuring principle

The measurement principle is based on the reaction of the artificial radical generator 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH) with the fluorescent dye fluorescein . The generated radicals oxidize the fluorescein; the oxidized fluorescein does not fluoresce. This reaction is slowed down or suppressed for a period of time when an antioxidant is present, as the radicals generated react with the antioxidant and not with the fluorescein. The reaction is observed over 60-90 minutes by measuring the fluorescence of the sample solution until it drops to zero; H. until all fluorescein molecules present are oxidized. The measured fluorescence can be shown graphically as a function of time. A sigmoid curve results . The area under this curve corresponds to the antioxidant capacity.

Trolox solutions of known concentration are used for quantification. These solutions are measured in the same way. A linear relationship between the measured area under the fluorescence-time curve and the Trolox concentration can be observed (within a certain concentration range) . So you can calculate which Trolox concentration would result in the same area as the measured sample.

Unit of measurement

The ORAC value is given in Trolox equivalents per unit volume or weight of the sample, e.g. B. µg TE / 100 g or µg TE / mL. The unit of measurement must always be specified when quoting an ORAC value, as e.g. B. the statement “The ORAC value is 100.” could mean both 100 µg TE / 100 g and 100 mg TE / g (or other units), so it is not clear and therefore not comparable.

Extensions

L-ORAC

For the measurement of fat-soluble antioxidants are acetone and as solubilizers methylated β- random cyclodextrin (randomly methylated β-cyclodextrins, rmcd) was added, then the fat-soluble antioxidants that in the otherwise aqueous reaction mixture solution. The ORAC value measured in this way is referred to as L-ORAC. The measurement method without RMCD can then be called H-ORAC for delimitation.

Total ORAC

To measure the effectiveness of antioxidants against various radicals, other radical generators besides AAPH can be used. This deviation from the Ou et al. described protocol can lead to different results. Therefore this deviation should be mentioned together with the result. The sum of the ORAC results from measurements with five different radical generators is marketed as "Total ORAC".

Cellular Antioxidant Activity (CAA)

In order to better simulate the situation in the body, the cellular antioxidant activity (CAA) can be measured. The measuring principle is analogous to that of the ORAC, but the reaction partners (including the antioxidant) must first be absorbed by the cells of a cell culture.

meaning

  • The ORAC value takes into account the complete course of the reaction, whereby antioxidants that prolong the lag time and antioxidants that slow down the reaction rate are comparable.
  • ORAC values ​​are comparable with one another, since the Ou et al. suggested protocol is usually observed.
  • The ORAC value describes a chemical property of the measured substance or food. Since the reaction taking place in the ORAC measurement does not take place in the body and since the bioavailability of the sample components is not known, no health effects can be inferred from the ORAC value.
  • Consumers associate the ORAC value (as evidence of antioxidant capacity) with positive health effects. Therefore, the ORAC value is used in marketing for food.

The United States Department of Agriculture (USDA) found in 2012 that there was no evidence of the free radical theory and the measurement was therefore irrelevant.

Individual evidence

  1. ↑ a b c Ou, Boxin, Hampsch-Woodill, Maureen, and Prior, Ronald: Development and validation of an improved oxygen radical absorbance capacity assay using fluorescein as the fluorescent probe in Journal of Agricultural and Food Chemistry . 49, 10, 2001, pp. 4619-4626, doi : 10.1021 / jf010586o .
  2. ↑ X. Wu, GR Beecher, JM Holden, DB Haytowitz, SE Gebhardt, RL Prior: Lipophilic and hydrophilic antioxidant capacities of common foods in the United States. In: Journal of agricultural and food chemistry. Volume 52, Number 12, June 2004, pp. 4026-4037, doi : 10.1021 / jf049696w , PMID 15186133 .
  3. ↑ Huang, Dejian, Ou, Boxin, Hampsch-Woodill, Maureen, Flanagan, Judith A., and Deemer, Elizabeth K .: Development and validation of oxygen radical absorbance capacity assay for lipophilic antioxidants using randomly methylated beta-cyclodextrin as the solubility enhancer in Journal of Agricultural and Food Chemistry 50, 7, 2002, pp. 1815-1821, doi : 10.1021 / jf0113732 .
  4. ↑ Press Releases - Brunswick Labs Introduces Next Generation Total ORAC for Food and Nutrition . Brunswick Laboratories website , April 20, 2009. Retrieved November 3, 2012.
  5. ↑ Wolfe, Kelly L., and Liu, Rui Hai: Cellular Antioxidant Activity (CAA) Assay for Assessing Antioxidants, Foods, and Dietary Supplements. in Journal of Agricultural and Food Chemistry 55, 22, 2007, pp. 8896-8907, doi : 10.1021 / jf0715166 .
  6. ↑ a b Withdrawn: Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods, Release 2 (2010) . United States Department of Agriculture, Agricultural Research Service. May 16, 2012. Retrieved November 3, 2012.