Wednesday, October 2, 2019
ORAC (oxygen radical absorbance capacity) assay and other methods for the evaluation of antioxidants :: essays research papers
1. Introduction Most people know about antioxidants and belive in them as preventers against cell damage, which in the most severe case can cause cancer. Almost all nutritions contain a certain amount of antioxidant – both chemical and/or biological. To measure the activity and amount of the antioxidants present in a sample, some distinctive but easy assays have been established. This paper will give a short overview of the ORAC (oxygen radical absorbance cacpacity) assay and compare it with other antioxidant assays. Besides that, the paper introduces some preliminary results on antioxidant activity of the plant Apocynum venetum conducted by the author. Fig. 1 on cover page from [9] Table of Contents 1. Introduction     2 2. The ORAC assay – a brief introduction     4 3. Biochemical background of antioxidant activity     6 4. Comparison of ORAC with other antioxidant activity assays     7 5. Results in current research     8 6. Discussion and conclusions     9 References     10 2. The ORAC assay – a brief introduction 2.1 Theoretical background The oxygen radical absorbance capacity (ORAC) assay is a method for measuring the total antioxidant activity in a biological sample. Biological samples include body fluids of animals and humans (serum, plasma, urine, saliva), plant extracts, agricultural and food products, and pharmaceutical products.[6] The advantage of the ORAC assay is the wide range of applications as it can be used for both lipophilic and hydrophilic samples and compounds. Besides measuring the total antioxidant capacity, the assay can also qualitatively measure the amount of fast versus slow acting antioxidants in a sample. The principle of the ORAC is based on the following scheme: Fig. 2: Principal order of the ORAC assay[10] The sample contains a certain amount of compounds with an antioxidant activity. In water soluble samples, fluorescein is used as the probe which is protected by the antioxidants.[3] After adding a certain amount of a free radical, the loss in fluorescence over time is measured until the whole fluorescence is eliminated and the scavenging activity of the antioxidant is vanished. By integrating the area under the kinetic curve relative to the blank, the concentration of all antioxidants present in the sample can be calculated. Trolox, a water soluble tocopherol derivative, is used as a standard to calculate the antioxidant activity of the sample in trolox equivalents (μmol TE/g). 2.2 Fluorescein reaction Fluorescein belongs to the group of triphenylmethane dyes with a xanthene structure. Its fluorescence is based on the oxygen withdrawing groups and the intermittend double bounds shifting the wavelength towards the visible light range. Radicals can distubr this structure and erase the fluorescence by destructing one aromatic ring structure as seen in the reaction scheme.
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