Oxidative stress: do you know the ORAC index?

What can this abbreviation mean? Before defining what the ORAC index and its interests are, let’s 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 done, if this oxidative stress exists, it is because it plays indeed beneficial roles.Your immune cells, for example, need him to defend you against inflections, as well as the inflammation generated by an 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, local and localized oxidative stress. The higher consumption of oxygen in fact leads to an increase in oxidative stress, free radicals then stimulate the production of cytokines, resulting in a cascade of inflammatory reactions. Immune cells are recruited to the site of inflammation and will help “cleanse” and repair tissue damage.

However, when the productions are too important or the capacities of defenses insufficient, the same oxidative stress risks spreading. To protect itself, the body then has endogenous protection systems, enzymatic complexes present in the mitochondria and the cytosol of the cells:

  • Glutathione Peroxidase (GPx)  is formed of 4 subunits each containing a selenium atom incorporated into a selenocysteine ​​molecule.
  • Superoxide Dismutase (SOD) catalyzes the disproportionation of superoxide, a free radical formed during oxidative stress.
  • Catalase  allows the transformation of hydrogen peroxide.

The proper functioning of these endogenous systems is dependent on the presence of certain minerals, namely Zinc, Selenium, Manganese and Copper.

Regardless of these systems of internal protection of the body, the diet is full of powerful antioxidant molecules, the famous vitamins A, C and E , but also many plant active ingredients, such as the family of polyphenols . You can find some examples of antioxidants and their specific properties in my article on fruits and vegetables in 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: carbohydrate (so-called glycation mechanism), lipid (lipoperoxidation), protein, even the genetic information itself, the DNA structure, strongly favoring the processes carcinogenesis . In general, these oxidations contribute to the loss of functionality of the cells and to their accelerated aging. We can cite the oxidation of cholesterol, essential marker of cardiovascular protection. More than your LDL-cholesterol level (so-calledthe bad cholesterol ), it is indeed the  LDLox for LDL-oxidized , which increases the risks of atherosclerosis and more generally cardiovascular.

Everything is a question of balance … Still and always. Find moreover my article on the maladjustment to the effort,the roles of the food on the control of the inflammation or the relative interests of a taking of antioxidants in phase of recovery .

The ORAC index 

ORAC stands for ”  Oxygen Radical Absorbance Capacity  ” or Absorbency radicals derived from oxygen . This index makes it possible to determine the antioxidant power of a food. The idea is simple: the higher the ORAC index, the more food has quantitative antioxidant properties.

The measurement principle of the ORAC index is based on the free radical oxidation of a fluorescent probe (fluorescein) and on the ability of the antioxidants studied to absorb these free radicals. Like 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 (clearly, it is a synthetic analogue of vitamin E, but soluble in water).

Quantification is then measured by calculating the area under the curve of the test sample and comparing it to that of Trolox. You obtain then the ORAC index, expressed in μmol TE per 100 g of food (TE = Trolox equivalent): 1 ORAC unit is equivalent to the net protection by 1 micromole of Trolox.

Other measures 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 peroxides ROO •.
  • 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 the formation of the ABTS radical (ABTS • +) resulting from the reaction between the chemical compound ABTS (2,2′-azino-bis (3-ethylbenzothiazolin-6-sulfonic acid) )) and potassium persulfate (K2S2O8). The radical ABTS • + normally has a color from blue to green. The addition of antioxidants reduces the formation of this radical and leads to discoloration of the mixture, measured spectrophotometrically.

Advantages and limitations of the ORAC measure

Like any index, it is an average value, calculated on the basis of samples and to be considered accordingly. Depending on the cultivation method, storage and cooking, variations can be important for the same plant. In addition, the ORAC index does not consider the specificity of certain antioxidants (eg lutein is a significant contributor to the prevention of age-related macular degeneration of AMD ). Thus, a plant may have a relatively low ORAC index but be very interesting for a given indication: be careful not to rely solely on this index to judge the antioxidant quality of plants.

To optimize its antioxidant status outside of specific situations (intense activity, exposure to pollutants, UV, drug treatment, etc.), needs are estimated between 3000 and 5000 ORAC units per day, with a daily minimum of 2000 ORAC units.