The absorption capacity of oxygen radicals ( ORAC ) is a method of measuring antioxidant capacity in biological samples in vitro .
Various foods have been tested using this method, with certain spices, berries and nuts rated so high in the once-published table by the United States Department of Agriculture (USDA), but withdrawn in 2012 because there is no correlation between test results and biological activity may be determined, suggesting that there is no in vivo physiological evidence available to support the free radical theory.
Although not all of them unilaterally refuse, the majority position supports the USDA decision. Alternative measurements include Folin-Ciocalteu reagents, and trolox equivalent to antioxidant capacity tests.
Video Oxygen radical absorbance capacity
Metode
This test measures the oxidative degradation of fluorescent molecules (either beta-phycoerythrin or fluorescein) after being mixed with free radical generators such as the azo initiator compounds. Azo-initiators are thought to produce heating radicals, which destroy the fluorescence molecule, which causes the loss of fluorescence. Antioxidants are thought to protect fluorescent molecules from oxidative degeneration. The level of protection is quantified using a fluorometer. Fluorescent is currently most widely used as a fluorescent probe. Equipment that can automatically measure and calculate commercially available capacity (Biotek, Roche Diagnostics).
Fluorescent intensity decreases as oxidative degeneration progresses, and this intensity is usually recorded for 35 minutes after the addition of the azo-initiator (free radical generator). So far, AAPH (2,2'-azobis (2-amidino-propane) dihydrochloride) is the only free radical generator to use. Degeneration (or decomposition) of fluorescein is measured as the presence of antioxidants slowing the fluorescence decay. The decay curve (fluorescence intensity vs. time) was recorded and the area between two decay curves (with or without antioxidants) was calculated. Furthermore, the antioxidant-mediated protection level is quantified using an antioxidant trolox (analog vitamin E) as the standard. Different trolox concentrations are used to create standard curves, and test samples are compared with these. Results for the test samples (food) have been published as "trolox equivalents" or TEs.
One of the benefits of using the ORAC method to evaluate the antioxidant capacity of the substance is that it takes into account samples with and without lag phase their antioxidant capacity. This is especially useful when measuring foods and supplements containing complex ingredients with a variety of slow and fast antioxidants, and ingredients with unexpected compounded effects.
The disadvantages of this method are: 1) only certain antioxidant activity against a particular radical (perhaps mainly peroxy) is measured; However, the formation of peroxyl radicals has never been proven; 2) the nature of the destructive reaction is not characterized; 3) there is no evidence that free radicals are involved in this reaction; and 4) there is no evidence that ORAC values ​​have biological significance after any food consumption. In addition, the relationship between the value of ORAC and the health benefits has not been established.
The result of the scientific rebuttal of the ORAC physiological significance, USDA, which has compiled and published ORAC data for more than a decade, attracted the publication of the ORAC value for American public food in May 2012.
Several modified ORAC methods have been proposed. Most of them use the same principle (ie AAPH-radical measurements that are mediated by fluorescein damage); however, ORAC-EPR, a paramagnetic electron-based ORAC resonance method directly measures a decrease in AAPH radical levels by the action of flushing of antioxidants.
Maps Oxygen radical absorbance capacity
The rules guide
In the following discussion, the term "antioxidants" refers primarily to non-nutrient compounds in foods, such as polyphenols, which have antioxidant capacity in vitro , thus providing an artificial index of antioxidant power - ORAC measurements.
In addition to dietary vitamin antioxidants - vitamin A, vitamin C and vitamin E - no food compounds have been demonstrated with the antioxidant properties of in vivo . Thus, regulators such as the US Food and Drug Administration and the European Food Safety Authority (EFSA) have published guidelines prohibiting the labeling of food products to claim or imply antioxidant benefits when there is no such physiological evidence. This guide to the United States and the EU sets it illegal to imply potential health benefits on product package labels with high ORAC.
Context physiological
Although in vitro studies show that polyphenols are a good antioxidant and may affect the value of ORAC, the antioxidant effects of in vivo may be negligible or absent. With an undefined anti-oxidant mechanism, flavonoids and other polyphenols can reduce the risk of cardiovascular disease and cancer.
As interpreted by Linus Pauling Institute, EFSA and USDA, food polyphenols have little or no value of antioxidant food directly after digestion. Unlike controlled test tube conditions, the fate of polyphenols in vivo shows that they are not well preserved (less than 5%), with most of what is absorbed exists as chemically modified metabolites aimed at for quick excretion.
Increased blood antioxidant capacity seen after consumption of rich foods polyphenols (ORAC-rich) is not directly caused by polyphenols, but most likely the result of elevated levels of uric acid derived from flavonoid metabolism. According to Frei, "we can now follow the activity of flavonoids in the body, and one thing that is clear is that the body sees them as foreign compounds and tries to get rid of them."
Food source
The value is expressed as the sum of the antioxidant fraction (eg carotenoids) and soluble in water (eg phenolic) (ie, "ORAC total") reported in micromoles trolox equivalent (TE) per 100 gram sample and compared with total polyphenol content in the sample.
These values ​​are considered biologically irrelevant by EFSA and USDA.
With almost all vegetables, conventional boiling can reduce ORAC values ​​by up to 90%, while steam contains more antioxidants.
Comparison of ORAC values ​​
The US Department of Agriculture, previously an ORAC data publisher, drew the publication of the ORAC value for American public food in 2012 due to the lack of scientific evidence that ORAC has biological significance.
When comparing ORAC data, care should be taken to ensure similar units and foods are compared. Some evaluations will compare ORAC units per gram of dry weight from whole foods or ground powder, others will evaluate ORAC units in fresh or frozen wet weight, and others will see ORAC units per serving. Under each evaluation, different foods may appear to have higher ORAC values. For example, although the raisins do not have more antioxidant potential than the grapes from which they are dried, the raisins will appear to have a higher ORAC value per gram of wet weight than grapes due to the reduced water content. Similarly, the large water content in the watermelon can make it appear as if the fruit is low in ORAC. Similarly, the amount of typical food used should be considered; herbs and spices may be high in ORAC, but are applied in much smaller quantities than whole whole foods.
Many health food and beverage companies and marketers have misplaced ORAC ratings by promoting products claimed to be "high in ORAC". Since most of these ORAC values ​​have not been independently validated or subject to peer review for publication in scientific literature, they remain unconfirmed, can not be trusted scientifically, and may mislead consumers.
See also
- List of antioxidants in foods
- Polyphenol antioxidants
- Reduced potential
- Trolox (TEAC)
References
External links
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Xu, Baojun; Chang, Sam K.C. (2008). "The effect of immersion, boiling, and steaming the total phenolic content and antioxidant activity of the winter food legum". Food Chemistry . 110 (1): 1-13. doi: 10.1016/j.foodchem.2008.01.045. PMID 26050159.
Source of the article : Wikipedia
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