The Oxygen Radical Absorbance Capacity is the ability to bind oxygen radicals. The vitamin E derivative Trolox is used as a reference value for measurement. The ORAC value is mainly used for food.
How is the measurement done exactly?
Antioxidants are divided into fat-soluble and water-soluble. The measurement of water-soluble antioxidants is called H-ORAC, that of fat-soluble ones L-ORAC. In addition, there are other methods to determine the binding value of free radicals. These include FRAP and TEAC. ORAC measurement controls the entire course of the antioxidant reaction
The reactions are tested by generating artificial radicals and measuring them. This is done with the dye fluorescein. The generated radicals oxidise the dye. As a result, the dye no longer fluoresces. The presence of an antioxidant stops this for a certain period of time. The duration is usually between 60 and 90 minutes. During this time, the decrease in fluorescence is measured continuously until it reaches zero. The graphical representation is called a sigmoid curve. The area under the curve represents the antioxidant capacity.
Basically, a distinction is made between qualitative and quantitative measurement. In addition to the qualitative method already described, the quantitative ORAC measurement makes use of the Trolox solution, which is examined in a similar way. Here, the linear relationship between the Trolox concentration and the area under the fluorescence-time curve is considered.
In which unit of measurement is the ORAC value measured?
This is given in Trolox equivalents per unit of volume and weight of the sample solution ( µg TE/100 g or µg TE/mL).
The L-ORAC method
In this variant, fat-soluble antioxidants with acetone and randomly methylated cyclodextrin (RMCD) are used for measurement. This results in the dissolution of the fat-containing antioxidants. The measured value is called the L-ORAC value
What does Total ORAC mean?
If the effectiveness of antioxidants against different radicals is to be measured, both radical generators and AAPH are used. Depending on what is used, the results will vary. Therefore, it is important to mention the differences with the result. The sum of all ORAC values from measurements with five different radical generators is called Total ORAC
What is the significance of the ORAC value?
The entire course of the reaction is taken into account. This makes both antioxidants that extend the lag time and those that extend the reaction rate comparable. The ORAC values can be compared with each other. The Ou et al protocol is observed. The binding of free radicals is important for the human body. The numerous methods offer a broad spectrum. Foods high in vitamins and minerals are considered good antioxidants