Oxygen Radical Absorbance Capacity

Using the Oxygen Radical Absorbance Capacity (ORAC; German: ability to scavenge oxygen radicals ), the antioxidant capacity of a sample are given. In measuring the vitamin E derivative is Trolox as a reference, so the result is given in Trolox equivalents. The ORAC value is often intended for food.

The ORAC measurement is applicable to water-soluble ( or H- ORAC ORAC) and fat-soluble antioxidants ( L- ORAC). Compared with other methods for the determination of antioxidant capacity (eg TEAC, FRAP ), the antioxidant response throughout their course observed in the ORAC measuring and measured not only at a specific time.

Principle of measurement

The principle of measurement 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 or suppressed for a certain time, when an antioxidant is present, since the radicals produced react with the antioxidant and not with the fluorescein. The reaction is monitored for 60-90 minutes by the fluorescence of the sample solution is measured until it drops to zero, that are oxidized to all the existing fluorescein molecules. Measured fluorescence can be represented graphically as a function of time. This results in a sigmoidal curve. The area under this curve corresponds to the antioxidant capacity.

To quantify serve Trolox solutions of known concentration. These solutions are likewise measured. This can be ( in a given concentration range ) is a linear relationship between the measured surface observed under the fluorescence versus time curve and the Trolox concentration. Thus, one can calculate which Trolox concentration would result in the same area as the measured sample.

Unit of measurement

The ORAC value is expressed in Troloxäquivalenten per volume or per unit weight of the sample, eg TE/100 ug g or ug TE / mL. The unit must always be specified when naming an ORAC value, as for example the statement " The ORAC value is 100 " both 100 micrograms TE/100 g and 100 mg TE / g ( or other units ) could mean, so do not clear and are therefore not comparable.

Extensions

L- ORAC

For the measurement of fat-soluble antioxidants are acetone and randomly methylated β as solubilizers -cyclodextrin ( randomly methylated β - cyclodextrins rmcd ) was added to remove any loose the fat-soluble antioxidants in the otherwise aqueous reaction mixture. The measured ORAC value is referred to as L- ORAC. The measurement method without rmcd can then be called to distinguish H- ORAC.

Total ORAC

To measure the effectiveness of antioxidants to various radicals, other radical generators can be used except AAPH. This deviation from that of Ou et al. protocol described 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 free radical generators is marketed as "Total ORAC ".

Cellular antioxidant activity (CAA )

To better simulate the situation in the body that can be measured the cellular antioxidant activity ( cellular antioxidant activity, CAA ). The measurement principle is analogous to the ORAC here, however, the reactants (including the antioxidant ) must first be taken up by the cells of a cell culture.

Importance

• The ORAC value takes into account the entire course of the reaction, thus antioxidants that prolong the lag time, and antioxidants, which slow down the reaction rate, are comparable.
• ORAC values ​​are comparable because the. Ou et al proposed protocol is commonly observed.
• The ORAC value describes a chemical property of the measured substance or foodstuff. Since the running at the ORAC measurement reaction does not take place in the body, and since the bioavailability of the sample components is not known, no health effect can be concluded from the ORAC value.
• The ORAC value ( as proof of antioxidant capacity) of consumers associated with positive health effects. Therefore, the ORAC value is used in marketing for food.