ORAC - A MEASURE OF ANTIOXIDANT CAPACITY*
The ORAC (Oxygen Radical Absorbance Capacity) unit, or ORAC value, or ORAC score, is a method of measuring the antioxidant capacity of different foods and supplements.
The Need for Antioxidants
Antioxidants are substances that protect the cells of the body from damage caused by free radicals. Some antioxidants are produced by the body such as superoxide dysmutase (SOD). Certain vitamins are ‘antioxidants’ such as vitamins C and E, and different foods have antioxidant properties.
The need for antioxidants is a recurring theme in many of my newsletters, as well as in the increasing literature available on health issues. My January 2007 newsletter Free Radicals – Antioxidants and my January 2010 newsletter Phytochemicals have a detailed description of free radicals and the way in which antioxidants give protection against the damage that they can cause.
The positive impact of diets high in fruits and vegetables is now becoming widely accepted, and such diets are strongly recommended in the prevention of disease, such as for example cancer (refer to my March 2008 newsletter Prevention of Cancer). Fruits and vegetables have a significant antioxidant capacity, and it is believed that the benefits of a diet high in fruits and vegetables are due, in part, to the presence of antioxidants.
Oxygen Radical Absorbance Capacity (ORAC) is a method of measuring the antioxidant capacity in foods, thus providing guidelines as to which foods are likely to provide the best antioxidant protection against disease, as well as against aging (accelerated by free radical damage).
The ORAC is expressed as a number. This is variously called ‘unit’, ‘score’ or ‘value’. It was developed by scientists at the National Institutes of Health, Washington D.C., USA. Although the exact relationship between the ORAC value of a food and its health benefit has not been fully established, it is believed that foods higher on the ORAC scale will be more effective in neutralising free radicals and preventing or reducing the potential damage caused by them.
How is the ORAC measured?
It is done by an assay technique, and the following is but a brief overview of this. The assay measures the oxidative degradation of a fluorescent molecule (for example fluorescein) after being mixed with free radical generators. Azo-initiators are such substances and are considered to produce the peroxyl radical by heating, which damages the fluorescent molecule, resulting in the loss of fluorescence. Antioxidants are able to protect the fluorescence molecule from the oxidative degeneration. The degree of protection is quantified using a Fluorometer.
The fluorescent intensity decreases as the oxidative degeneration proceeds, and this intensity is recorded for 35 minutes after the addition of the azo-initiator (free radical generator). The degeneration or decomposition of fluorescein is measured and reflects the presence of antioxidants which slow the fluorescence decay.
One of the benefits of using the ORAC method to evaluate substances’ antioxidant capacity is that it takes into account samples with and without lag phases of their antioxidant capacities. This is especially beneficial when measuring foods and supplements that contain complex ingredients with various slow and fast acting antioxidants.
Subsequently, the degree of antioxidant-mediated protection is quantified using the antioxidant trolox (a vitamin E analogue) as a standard. Results for test samples (foods) have been published as “trolox equivalents” or TE.
One of the drawbacks of this method is that there is no evidence that free radicals are involved in this reaction and that only antioxidant activity against peroxyl radicals is measured.
Comparisons of ORAC Values
When comparing ORAC data, care must be taken to ensure that the units of food being compared are similar. Some evaluations will compare ORAC units per grams of dry weight, others will evaluate ORAC units per grams wet weight and still others will look at ORAC units per serving.
As a result, different foods can appear to have higher ORAC values. For example, although a raisin has no more antioxidant potential than a grape from which it was dried, raisins will appear to have a much higher ORAC value per gram than grapes due to their reduced water content. Similarly, watermelons, very high in water content, would appear to be very low in antioxidants.
Likewise, when comparing ORAC data, the typical quantity use in food preparation should be considered: herbs and spices can be nutritionally dense, but are used in very small quantities.
Recently, a number of ‘health’ food companies have capitalised on the ORAC rating, selling concentrated supplements that they claim to be “the number one product, based on the high ORAC value”.
ORAC Values of Foods
In 2007, scientists with the United States Department of Agriculture published an updated list of ORAC values for 277 foods commonly consumed by the U.S. population (fruits, vegetables, nuts, seeds, grains, spices etc.). Values were expressed as the sum of the lipid soluble (e.g. carotenoid) and water-soluble (e.g. phenolic) antioxidant fractions, i.e. “total ORAC” reported as in micromoles Trolox equivalents (TE) per 100 gram sample. [Nutrition Data Laboratory, Agriculture Research Service, US Department of Agriculture, Oxygen radical absorbance capacity (ORAC) of Selected Foods - 2007]
http://optimalhealth.cia.com.au/OracLevels.htm gives the ORAC levels of some common foods. The results for some 80 foods are set out in three different ways on this website:
1) The ORAC results for foods, per 100 grams, grouped as fruits, juice/supplements, vegetables and oils (highest to lowest in each grouping)
2) Foods sorted by ORAC result / 100g (highest to lowest)
3) Foods sorted by ORAC result / calorie (highest to lowest).
The following is but a small sample, set out as in 1) above, to illustrate this way of measuring the antioxidant content of foods and to help you to interpret ORAC figures when they appear on food labels and in the literature.
Food (100 grams)
|ORAC/100 grams||calories/100 grams||ORAC/calorie||ORAC/gram|
|Juice/Supplement/ misc foods|
|Vit. C (1.89 /mg)||189,000||-||-||1,890|
|Vit. E (1.35/ IU / mg)||135,000||-||-||1,350|
The above ORAC values are based on actual weight, namely 100 grams. Unfortunately other data is less precise, for example that based on ‘serving size’, which can make it difficult to compare results.
The ‘Serving Size’ in the USDA data, from the publication by the Nutrition Data Laboratory referred to above, includes the following, by way of example:
|Beans, Kidney||½ cup dried|
|Apple, Red Del.||1 apple|
|Apple, G. Smith||1 apple|
|Potato||1 cooked potato|
It can be seen how imprecise ‘serving size’ is. How large is the apple or potato? Why ½ cup for some and 1cup for other foods?
Much more work needs to be done to obtain reliable and reproducible data. Independent of the weight, dried/raw or serving size is the nutritional value of the foods tested. This is linked to the quality of the soil, whether organically grown, sun ripened etc.
Meat contains inherent substances that protect it from degradation. Vitamin E, carnosine, glutathione, selenium and conjugated linoleic acid are among its most notable antioxidants. Http://www.nutritiouslife.com/pdf/orac_points_portable_guide.pdf lists the ORAC values of all the fruits, vegetables, nuts, grains, herbs etc, as in the other websites that set out ORAC values. However it also lists the various meats (poultry, seafood, lamb, beef, game and pork), and it indicates that all meats “have no current tested ORAC values”.
The ORAC value of a food gives some indication of the inherent antioxidant potential of that food.
It is but a guide, and care must be exercised in interpreting the data.
A diet high in fruits and vegetables is a healthy diet. It is high in alkalinity (see my September 2005 newsletter Acid/Alkaline Balance - The Ideal Diet) and all fruits and vegetables have some level of antioxidant activity. It must be remembered that fruits and vegetables also contain a wide range of other phytochemicals which contribute to their health benefits.
A healthy diet of fruit and vegetables should contain a significant amount of raw foods. The reasons for this recommendation are set out in my April 2007 newsletter Cooked Food is Poison - Why Raw is Better.
Another reason for raw vegetables is that cooking them reduces the ORAC values significantly. Steaming vegetables, when cooking is required, is the least destructive to the antioxidants.
*Copyright 2010: The Huntly Centre.
Disclaimer: All material in the Huntlycentre.com.au website is provided for informational or educational purposes only. Consult a health professional regarding the applicability of any opinions or recommendations expressed herein, with respect to your symptoms or medical condition.
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