What does this abbreviation mean? Before defining what the ORAC index and its interests are, let us remember that oxidative or oxidative stress ...
What is oxidative stress?
Free radicals, or ROS (Reactive Oxygen Species), are unstable molecules derived directly from respiration. About 2% of the oxygen consumed is at the origin of the production of these free radicals. It is therefore a permanent physiological mechanism indispensable to life. Nature being well made, if this oxidative stress exists, it is because it plays indeed beneficial roles. Your immune cells need it for example to defend you against inflections, as well as inflammation generated from injury or surgery is essential to enable the healing process.
The cellular adaptation to the regular effort and the resulting increase in performance is also conditioned by the existence of controlled oxidative stress, punctual and local. The higher oxygen consumption causes an increase in oxidative stress, the free radicals then stimulate the production of cytokines, resulting in a cascade of inflammatory reactions. Immune cells are recruited from the site of inflammation and will help to "clean" and repair tissue damage.
However, when the productions are too large or the defensive capacities insufficient, the same oxidative stress may spread. To protect itself, the organism then has endogenous protective systems, enzymatic complexes present in the mitochondria and the cytosol of the cells:
- Glutathione Peroxidase (GPx) is composed of 4 subunits, each containing a selenium atom incorporated in a selenocysteine molecule.
- Superoxide Dismutase (SOD) catalyses the disproportionation of superoxide, a free radical formed during oxidative stress.
- Catalase allows the conversion of hydrogen peroxide.
The proper functioning of these endogenous systems is dependent on the presence of certain minerals, namely Zinc, Selenium, Manganese and Copper.
Independently of these systems of internal protection of the body, the diet abounds with powerful anti-oxidant molecules, the famous vitamins A, C and E, but also many plant actives, such as the family of polyphenols. You can find some examples of anti-oxidants and their specific properties in my article on fruits and vegetables of November or December.
When your diet is insufficiently rich in antioxidants, logically the risks of prolonged and uncontrolled oxidative stress increase, those of the cellular attack with. The excess of free radicals will indeed alter many cellular structures: carbohydrates (so-called glycation mechanism), lipids (lipoperoxidation), proteins, even the genetic information itself, the structure of DNA, strongly favoring the processes Of carcinogenicity. In general, these oxidations contribute to the loss of functionality of the cells and to their accelerated aging. One can thus cite the oxidation of cholesterol, essential marker of cardiovascular protection.
More than your LDL-cholesterol level (so-called wrong bad cholesterol), it is indeed the LDLox for LDL-oxidized, which increases the risks of atherosclerosis and more globally cardiovascular.
Everything is therefore a matter of balance ... Again and again. Find also my article on the disadaptation to the effort, the roles of the food on the control of the inflammation or the relative interests of a taking of antioxidants in recovery phase.
The ORAC index
ORAC is the acronym for "Oxygen Radical Absorbance Capacity" or Absorption Capacity of Oxygen Derived Radicals. This index determines the antioxidant power of a food. The idea is simple: the higher the ORAC index, the more quantitatively the food has antioxidant properties.
The principle of measuring the ORAC index is based on the oxidation by free radicals of a fluorescent probe (fluorescein) and on the ability of the antioxidants studied to absorb these free radicals.
Following the example of glucose for the glycemic index, the reference antioxidant used for ORAC measurements is Trolox, an abbreviation for the slightly more barbaric name of 6-hydroxy-2,5,7,8-tetramethylchroman- 2-carboxylic acid (clearly, it is a synthetic analogue of vitamin E, but soluble in water).
The quantification is then measured by calculating the area under the curve of the sample tested and comparing it to that of the Trolox.
You then obtain the ORAC index, expressed in μmol TE per 100 g of food (TE = Trolox equivalent): 1 unit ORAC is equivalent to the net protection by 1 micromole of Trolox.
Other measurements are also used to quantify the antioxidant capacity of food samples or biological samples. For example, the values:
TRAP: Total Radical-trapping Antioxidant Parameter. In the same way as the ORAC test, it evaluates the antioxidant activity by trapping different radicals, such as ROO peroxides.
FRAP: Ferric ion Reducing Antioxidant Power. It measures the antioxidant capacity of foods according to their ability to reduce ferric ions to ferrous ions.
TEAC: Trolox Equivalence Antioxidant Capacity. This method is based on the ability of a sample to inhibit ABTS (ABTS +) formation resulting from the reaction between the chemical compound ABTS (2,2'-azino-bis (3-ethylbenz-thiazoline-6-sulfonic acid )) And potassium persulfate (K2S2O8).
The ABTS + radical normally has a color from blue to green.
The addition of antioxidants reduces the formation of this radical and causes a discoloration of the mixture, measured by spectrophotometry.
Advantages and limitations of the ORAC measure
Like any index, this is an average value, calculated on the basis of samples and to be considered accordingly. Depending on the method of cultivation, preservation and cooking, variations may be important for the same plant. Moreover, the ORAC index does not consider the specificity of certain antioxidants (eg lutein plays a significant role in the prevention of AMD for Age-Related Macular Degeneration).
Thus, a plant may possess a relatively low ORAC index but be very interesting for a given indication: so be careful not to rely solely on this index to judge the antioxidant quality of the plants.
To optimize its antioxidant status outside of specific situations (intense activity, exposure to pollutants, UV, drug treatment, etc.), the needs are estimated between 3000 and 5000 ORAC units per day, with a daily minimum of 2000 ORAC units .