Should We Ditch the ORAC Antioxidant Test?


Is the ORAC assay still valuable, despite its controversies?

Free radicals support human health. If in excess, however, they can alternatively cause oxidative damage to cells and contribute to aging or even the development and progression of degenerative diseases.

Fortunately, evidence indicates that antioxidant substances may help combat excessive free radical production in the body. Normally, the body maintains a balanced production of free radicals and antioxidants. But when free radical production overwhelms the body’s antioxidant supply and hence its ability to temper free radical bioactivity, some other intervention is needed. This is where dietary antioxidants come into play.

While exogenous dietary sources of antioxidants do not have a direct effect on tempering free radical overproduction, these sources can help stimulate increased production of antioxidants within the body-to the point that balance between free radicals and antioxidants is restored.

In recent decades, much effort has been invested in identifying dietary substances of high antioxidant potential. As part of these efforts, analytical methods, or assays, have been developed specifically to measure the antioxidant content in food substances.

Without a doubt, the assay most publicized thus far has been the oxygen radical absorbance capacity (ORAC) assay. ORAC is a robust analytical method that emerged more than two decades ago, developed by scientists working at the National Institutes of Health (NIH) and USDA.

The ORAC assay determines the antioxidant potential of foods, botanicals, and biological samples. It is an in vitro test that can measure to what degree a substance of interest can scavenge various free radicals.

Importantly, ORAC cannotbe used to predict what effect or benefit an antioxidant substance will have within the human body in attenuating free radical production or coping with oxidative stress. As an in vitro test, ORAC cannot predict such in vivo effects-nor can any other chemical assay.

Over the past few decades, ORAC has seen both skyrocketing popularity as well as sharp criticism over whether it is a valuable assay at all-especially in light of newer assays. In this article, we discuss the rise, the fall, and the promise of ORAC.


How ORAC Began

ORAC started as a brainstorm in the 1980s between two USDA scientists commuting to the same lab in Boston. One of the commuters, a noted neuroscientist named Jim Joseph, PhD, had focused his laboratory studies on antioxidant-rich foods, such as blueberries, cranberries, strawberries, walnuts, and acai. Dr. Joseph mentioned to his fellow USDA commuter Ronald Prior, PhD, that he needed a way to determine the free radical–scavenging capacity of foods because he believed some foods might contribute to delaying the development of certain neurodegenerative diseases. First, Dr. Joseph needed a validated and precise way to measure free radical–scavenging capacity.

The ORAC assay was ultimately invented by Guohua Cao, MD, PhD, at NIH’s National Institute on Aging in Baltimore. Dr. Cao then developed the assay in the lab of Dr. Prior and Richard Cutler, PhD, at the Jean Mayer Human Nutrition Research Center on Aging at Tufts University, Agricultural Research Services, USDA.

USDA realized early on that the ORAC assay could be used to determine which fruits and vegetables have high antioxidant potential-and consequently might protect consumers against certain diseases. There was also a growing understanding that certain compounds-beyond just vitamins C and E or beta-carotene in fruits and vegetables-have strong antioxidant capacity. Scientists soon became very interested in measuring the antioxidant capacity of a range of fruits and vegetables to determine which ones people should eat in order to lower their risk of diseases associated with free radical pathology.

By 1991, the first version of the ORAC assay caught the attention of food scientists.1 Two years later, the assay was modified, automated, and capable of measuring antioxidant capacities of biological samples.2 By 1999, an improved and validated ORAC assay was developed-and continues to be the standard by which labs perform this assay around the world today.3


What Is ORAC?

The ORAC assay can quantify the scavenging activity of a food, compound, or agent to a single free radical anion, the peroxyl radical. This peroxyl radical is the most abundant free radical produced in the human body. Under conditions of oxidative stress, and due to a failure of indigenous antioxidants to stop its production, peroxyl radical levels can rise and damage cells and tissue-kind of like a “fender bender” on the freeway that just keeps hitting one car after another, for miles.

The improved ORAC assay introduced in 1999 relies on a common fluorescent probe, fluorescein, to monitor antioxidant activity. A microplate reader capable of detecting fluorescence can perform the assay in a 96-well or 48-well microplate format. This allows the ORAC assay to test many substances within a short period of time. Due to ORAC’s low cost and reproducibility between labs, the assay became a favorite of food scientists as they sought to identify foods with higher levels of antioxidant compounds. ORAC’s intra-assay precision made it particularly useful as a starting point for determining whether a substance might have characteristics able to attenuate free radical pathology.

The ORAC assay has further evolved over time. For instance, as scientists gained more understanding of the variety of free radicals in the human body, it became necessary to determine the scavenging activity of the five major radicals produced in the human body: hydroxyl radical, peroxyl radical, peroxynitrite, singlet oxygen, and superoxide anion. When at normal levels, these five free radicals play an essential and vital role in supporting the immune system’s ability to kill pathogens such as bacteria. However, when overproduced, they not only harm pathogens but also healthy cells. Keeping production of these five free radicals within a desirable range to support immune function is critical. In 2009, a new version of the ORAC assay was developed to quantify the scavenging capacity of all five important free radicals, individually or in combination. When the scores are combined, the resulting number offers scientists a Total ORAC for Food and Nutrition (TOTAL ORAC FN) unit value per gram. (Read more on this Total ORAC assay in the sidebar below.)


The Rise of ORAC

By the beginning of this century, USDA decided it could use ORAC to test virtually every food in the American diet-particularly foods suspected of having high antioxidant capacity, such as fruits, vegetables, and nuts. Within a few years, the results of such testing appeared in a series of papers published in various nutrition journals.

USDA used these results to build-and, in 2010, to publish-an independent, non-commercial database of verified ORAC scores for hundreds of foods. Notably, USDA made sure that its process for gathering food for testing reflected the way consumers obtain their food in the real world5-that is, USDA purchased foods in the marketplace just as consumers would do. Foods were selected during different seasons and in different forms (jellies, juices, purees, etc.). Each food item was then sent to a central USDA lab, freeze-dried (if purchased fresh) to remove almost all of its moisture content, and forwarded to another USDA lab where experienced chemists performed the ORAC assays. In this way, the ORAC value of each food was added to USDA’s ORAC database.

As ORAC captured public attention, companies began citing ORAC values to market their products’ antioxidant benefits, believing consumers assume that a product with a higher ORAC score is better than a product with a lower score. Hence began what some called the “ORAC race,” with companies striving to pit their products’ ORAC values against their competitors’.

As ORAC competition grew fierce, some of the most dubious ORAC claims I noted in the marketplace at the time came from ingredient suppliers at industry trade shows. For example, at a trade show, several ingredient firms marketing maqui berry (Aristotelia chilensis) displayed bar graphs promoting the berry as having a significantly higher ORAC score than such USDA-tested foods as acai, cranberries, and wild blueberries. When I asked the ingredient suppliers for the substantiation supporting these claims, one company merely responded that its product is a “maqui complex,” whatever that means.

Another ingredient supplier failed to realize or specify that USDA reports ORAC values in per gram measurements. As such, the ORAC assay result displayed on the company’s bar graph in marketing materials actually represented ORAC values per 100 grams; thus, the maqui product being promoted actually had an ORAC score that was 1/100th the ORAC value being touted. But when I asked that company to disclose the published scientific journals from which it had obtained the ORAC score claimed for its maqui, the company said the results had not been published but instead were obtained from ORAC testing performed by a leading laboratory. After the trade show, I contacted that laboratory and asked it to verify the results the ingredient supplier reported. The laboratory said the numbers the company used did not reflect the assay results the lab had provided-and, moreover, that the results the laboratory had provided did notreport ORAC values per 100 grams, as the company’s graph indicated. 

To one company’s credit, upon being alerted to its errors, the company promised to immediately remove the bar graph from its booth. Still, I can remember seeing a professor of nutrition from Chile who had seen the display expressing frustration on the trade show floor about such misleading information, stating that this kind of misinformation only hurt the image and reputation of an otherwise nutritious food.

As manufacturers became convinced that products needed a high ORAC value in order to sell competitively, and companies began leveraging their ORAC numbers to infer products were somehow superior, some unscrupulous firms even resorted to spiking products with antioxidants simply to increase their ORAC score. Additionally, laboratories began reporting extraordinarily high ORAC scores. When questioned on whether or not products may have been antioxidant-spiked, many contract laboratories pointed out that they had merely been asked to perform the ORAC assay, not characterize the product for the presence of any undeclared antioxidant agents that could have significantly raised the score.

Other cases of misleading data occurred when companies made questionable comparisons of the ORAC values of dietary supplement ingredients and the ORAC values of food ingredients. For example, a company claiming that consuming a gram of its supplement was equivalent to consuming 10 fruits and vegetables had intentionally selected fruits and vegetables in the USDA ORAC database that had very low ORAC values, such as a head of lettuce and a watermelon. Obviously, this is not the fairest or most honest comparison.


ORAC Backlash

As companies competed on ORAC values, companies whose products have lower ORAC scores-such as goji or mangosteen-had to vie for the attention of consumers who had become very interested in foods with high ORAC scores, such as acai, blueberries, strawberries, and cranberries. These companies soon realized that consumers were spending their dollars on foods with higher ORAC scores. Frustrated, these firms began raising questions about the utility and value of the ORAC assay. In part-and rightfully so-the companies pointed out that foods have other beneficial attributes beyond antioxidant capacity alone, such as anti-inflammatory bioactivity.

As these critics spoke out, questions and controversy surrounding ORAC grew. Scientists became concerned that too much marketplace emphasis was being placed on ORAC scores alone. After all, they pointed out, ORAC is an in vitro test, and its results cannot automatically be assumed indicative of any in vivo benefits when a food substance is in the human body. Although the layman consumer might not understand this crucial point, ORAC in fact was not established to predict whether a high-ORAC food or compound will have a high level of free radical scavenging activity in the human body. For instance, a review paper on antioxidant assays appeared in a noted scientific journal stating: “Any claims about the bioactivity of a sample based solely on assays such as ORAC, TEAC, and FRAP, etc., would be exaggerated, unscientific, and out of context. Moreover, these assays do not measure bioavailability, in vivo stability, retention of antioxidants by tissues, and reactivity in situ.8 The authors of that review paper concluded that assays such as ORAC, TEAC, and FRAP “bear no similarity to biological systems” and that how the compounds impact endogenously produced antioxidants cannot be seen in a lab assay; reactions or benefits observed during oxidative stress cannot be measured in the lab. 

And, as the number of in situ in vivo studies (somewhere in between in vitro and in vivo studies) of foods or nutraceutical products progressed, it became evermore apparent that the ORAC score of a food or compound does not always predict the degree to which a compound may be beneficial in the body.

As the scientific community grew frustrated by the marketplace overemphasis on ORAC, it eventually sparked a warning from scientists to those using ORAC numbers in the marketplace to be careful not to oversell or misrepresent what ORAC means. They urged marketers to use ORAC numbers responsibly.

Such warnings were issued to industry as early as 2004, including by myself and Ginny Bank in an article written for industry trade journal Nutraceuticals World.6 In that article, we provided the industry with a critical review of the strengths and weaknesses of the ORAC assay, pointing out that “with competitive use of ORAC values comes misconceptions and misuse.”

As we predicted, it did not take long before the marketplace became confused as to what ORAC numbers actually mean. The article we wrote forewarned that the “future of ORAC or any antioxidant assay will depend upon the responsible use of results when making comparisons.”7 The article also reminded the dietary supplements industry that “DSHEA clearly states that in advertising and marketing the ‘truthful and misleading’ yardstick should rule the day when making antioxidant unit comparisons.”

We also forewarned, “If comparisons are made, let them be made on the basis of sound analyses; otherwise the nutraceutical industry risks destroying the currency of ORAC in the minds of consumers as its value in product comparisons grows.”

Indeed, fast-forward, and today criticisms of ORAC abound. Many have come to question whether ORAC is a useful analytical method at all.

Abandoning ORAC? Not So Fast.

Unfortunately, due to the bad rap ORAC has received-and due to not giving enough credit to the assay’s value for what it is meant to target-some, including the USDA, have abandoned the ORAC method. Instead, these folks are now looking toward some of the newer assays that have since developed. (Read about some of these newer assays in the sidebar below.)

As mentioned earlier, in 2010, the USDA provided the public with a list of the ORAC values of virtually every food Americans consume.11 The list represents a decade worth of research conducted by the University of Arkansas at the USDA Arkansas Children’s Nutrition Center, as part of a study conducted under USDA’s National Food and Nutrient Analysis Program, as well as 40 sources in the scientific literature and other documents that were retrieved, reviewed, and critically evaluated for data quality.12

By documenting the ORAC values of a wide range of foods, USDA’s list served to verify claims made in the marketplace and expose and challenge those making false claims. The list was also a response to requests by the nutrition community, which said that knowing which foods have antioxidant compounds reflected by assays such as ORAC would help the industry to “identify those [foods] that are most likely to exert protective health effects.”13

But despite spending millions to determine the ORAC value of hundreds of foods, the USDA withdrew its ORAC tables from the Internet on May 16, 2012.14 Visitors to the USDA website now only see a statement explaining that “ORAC values are routinely misused by food and dietary supplement manufacturing companies to promote their products and by consumers to guide their food and dietary supplement choices.”

The site explains that, “Recently the USDA’s Nutrient Data Laboratory (NDL) removed the USDA ORAC Database for Selected Foods from the NDL website due to mounting evidence that the values indicating antioxidant capacity have no relevance to the effects of specific bioactive compounds, including polyphenols on human health.”

But many argue that ORAC does provide valuable information. In response to the USDA’s withdrawal of its ORAC value tables, Dr. Prior, who formerly headed USDA efforts to determine ORAC values in foods before retiring, released a statement15 pointing out that ORAC is still useful for identifying foods that have been separately shown to have in vivo health benefits. For instance, if in vivo studies have shown that intake of high-ORAC blueberries may impact cognitive health, then the ORAC assay can still be used to identify a high-ORAC blueberry.

Dr. Prior also argued that instead of writing ORAC off completely, we should abandon the expectation that “any one in vitro assay would truly reflect everything that happens” in our bodies.

I believe ORAC isa valuable tool, if we can accept ORAC for what it is: an assay that measures antioxidant content in vitro.

To see the value in ORAC, we must first accept that antioxidants have many beneficial functions and uses apart from what takes place in the human body alone, and that in these cases, it’s still valuable to measure in vitro antioxidant properties. Any discussion on the usefulness and utility of the ORAC assay should consider this point, and not just focus on the question of whether ORAC values correlate with in vivo studies.

ORAC, for instance, is useful for measuring antioxidant content for preservative purposes. In food science, antioxidants can be used to prevent fats in foods from becoming rancid. An example is what Native Americans discovered well before Europeans arrived in North America. Native Americans discovered that if they shredded red meat and mixed it with blueberries or bilberries, creating a food called pemmican, the antioxidants in the berries prevented the meat from going rancid to such an effective degree that the Native Americans could carry the dried mixture in a sack for months, without the mixture going rancid or causing food poisoning.

Likewise, the Institute of Medicine (IOM) defines antioxidant as “a substance in foods that significantly decreases the adverse effects of reactive species, such as reactive oxygen and nitrogen species, on normal physiological function in humans.”4 IOM’s antioxidant definition does not hinge solely on the question of whether a food’s antioxidant capacity in vitro correlates with its benefit in the human body in vivo; rather, the IOM’s broad definition of an antioxidant could include a substance that mitigates the oxygen reactive and nitrogen species that can adversely affect the quality and safety of foods. Significantly lowering the risk that such a food might be harmful to one’s health by inhibiting fatty acid autoxidation is a health benefit to humans.


ORAC’s Future

ORAC offers scientists a reproducible method with which to measure a food or a substance’s potential antioxidant capacity. It is a starting point for further study of a substance’s potential benefits, including benefits both within and outside of the body.

Take USDA’s ORAC database. This database provides useful data that we should consider when processing foods. For instance, an ORAC study on the effect of spray-dried blueberries led to the discovery that significantly higher retention of nutraceutical components occurred as levels of maltodextrin increased.19 ORAC studies have also shown that blackberry processing methods affect flavonoids and antioxidant capacity, depending on whether the berries are quick-frozen, canned in syrup, canned in water, pureed, or juiced (clarified or unclarified).20 Such studies illustrate how ORAC can indicate significant changes in antioxidant capacity and levels of bioactive compounds using different food storage methods.

This is still significant information.

The ORAC assay is not going away, despite efforts to urge its departure. Hopefully, the industry will recognize the importance of understanding the strengths and limitations of ORAC and will police those who misrepresent or mislead consumers. ORAC has evolved over two decades to become a useful validated tool in the hands of scientists and manufacturers. Let’s treat it as such. 


The author will provide readers of Nutritional Outlook a copy of the USDA’s ORAC database upon request.


Sidebar: Cell-Based Assays Now Compete with Chemical Assays

As ORAC’s popularity has grown, so have questions about its usefulness and the usefulness of other chemical antioxidant assays in predicting clinical outcomes. In response, several analytical labs have worked to develop other assay methods-some of which may be more predictive of in vivo effects. For instance, in the past few years NIS Labs (Klamath Falls, OR) and the company I represent, AIBMR Life Sciences (Puyallup, WA), have developed two cell-based antioxidant assays that more closely resemble what occurs in the human body.

The first assay is called the cell-based antioxidant protection in erythrocytes (CAP-e) assay. First presented to scientists at the 2008 annual gathering of the American Chemical Society, the CAP-e assay proved to be a welcome option by using human cells to measure biological responses to nutraceuticals.9 CAP-e also examines the effect of consuming a nutraceutical product to demonstrate that the results seen in vitro correlate with observed changes in serum seen in in vivo studies.10 

The second assay developed is the reactive oxygen species (ROS) formation in human polymorphonuclear (PMN) cells assay. This assay is based on the premise that antioxidant products are only of biological relevance if they are able to penetrate living cells and protect them from damage by free radicals.

In 2012, another laboratory, Brunswick Laboratories (Southborough, MA), introduced the intracellular antioxidant activity (CAA) assay. This cellular antioxidant assay assesses a substance’s ability to neutralize free radicals in living human cells. The CAA assay has allowed the lab to correlate the antioxidant properties of food in a biological environment with ORAC results.

Assays such as CAA, CAP-e, and ROS-PMN depend on a substance’s ability to be absorbed by cells. Hence, care needs to be taken when comparing the results of cell-based assays, given that lab technicians cannot mimic what happens in the gastrointestinal system. However, to date the results of clinical trials does show that there is a good correlation between cell-based assay results and observed changes in vivo.

Given the continuing demand for ORAC testing of nutraceuticals, Brunswick Laboratory in 2009 introduced the aforementioned Total ORAC for Food and Nutrition (TOTAL ORAC FN) assay, which measures antioxidant activity against five free radicals that occur in the human body: the hydroxyl radical, peroxyl radical, peroxynitrite, singlet oxygen, and superoxide anion. The TOTAL ORAC FN provides a combined score for all five radicals, which cause oxidative DNA, protein, and lipid damage seen in systemic chronic inflammation. It also provides a broader picture of what attributes a food or supplement might have that would not be obvious if limiting an antioxidant assay to a single free radical investigation. For example, although a tomato has a very low ORAC score when measured for its peroxyl radical scavenging capacity, it exhibits strong singlet oxygen quenching due to its carotenoid content.


  1. Cao G, Allessio HM, Cutler RG, “Oxygen-radical absorbance capacity assay for antioxidants,” Free Radical Biology in Medicine,1993; 14: 303-311.
  2. Wang H, Cao G, Prior RL, “Total antioxidant capacity of fruits,” Journal of Agricultural and Food Chemistry, 1996; 44: 701-705.
  3. Ou B, Hampsch-Woodill M, Prior RL, “Development and validation of an improved oxygen radical absorbance capacity assay using fluorescein as the fluorescent probe,”Journal of Agricultural and Food Chemistry,2001; 49: 4619-4626.
  4. Panel on Dietary Antioxidants and Related Compounds, Standing Committee on the Scientific Evaluation of Dietary Reference Intakes, Food and Nutrition Board. “Vitamin C, Vitamin E, Selenium, and Beta-Carotene and Other Carotenoids: Overview, Antioxidant Definition, and Relationship to Chronic Disease,” Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids, Washington DC: National Academy of Sciences, 2000: 35-57.
  5. Wu X, Gu L, Holden J et al., “Development of a database for total antioxidant capacity in foods: a preliminary study,” Journal of Food Composition and Analysis, 2004; 17: 407-422.
  6. Bank G, Schauss AG, “Antioxidant testing: an ORAC update,” Nutraceuticals World, 2004, 7(3): 68–71.
  7. Ibid, p. 70.
  8. Huang D, Ou B, Prior RL, “The chemistry behind antioxidant capacity assays,” Journal of Agricultural and Food Chemistry, 2005; 53: 1841-1856.
  9. Honzel D, Carter SG, Redman KA, et al., “Comparison of chemical and cell-based antioxidant methods of evaluation of foods and natural products: generating multifaceted data by parallel testing using erythrocytes and polymorphonuclear cells,” Journal of Agricultural and Food Chemistry, 2008; 56: 8319-8325.
  10. Jensen GS, Patterson KM, Barnes J, et al., “In vitro and in vivo antioxidant and anti–inflammatory capacity of an antioxidant–rich fruit and berry juice blend. Results of a pilot and randomized, double–blind, placebo–controlled, crossover study,” Journal of Agricultural and Food Chemistry, 2008: 56(18): 8326–8333.
  11. USDA National Nutrient Databank for Food Composition. Release 2. US Department of Agriculture, Agricultural Research Services. May 10, 2010.
  12. USDA National Nutrient Database for Standard Reference.
  13. Manach C, Scalbert A, Morand C, et al., “Polyphenols: food sources and bioavailability,” American Journal of Clinical Nutrition, 2004; 79: 727-747.
  15. Prior RL, “Antioxidant food databases? Valuable or not?”
  16. Farvid MS, Homayouni F, Kashkalani F, et al., “The association between oxygen radical absorbance capacity of dietary intake and hypertension in type 2 diabetic patients,” Journal of Human Hypertension, 2012 (June 14), Epub ahead of publication.
  17. Rautianinen S, Serafini M, Morgenstern R, et al., “The validity and reproducibility of food-frequency questionnaire-based total antioxidant capacity estimates in Swedish women,”American Journal of Clinical Nutrition, 2008; 87: 1247-1253.
  18. Rautianinen S, Larsoon S, Virtamo J, Wolk A, “Total antioxidant capacity of diet and risk of stroke: a population-based prospective cohort of women,” Stroke, 2012; 43: 335-340.
  19. Lim K, Ma M, Dolan KD, “Effects of spray drying on antioxidant capacity and anthocyanidin content of blueberry by-products,” Journal of Food Science, 2011; 76: H15-H164.
  20. Hager TJ, Howard LR, Prior RL, “Processing and storage effects of monomeric anthocyanins, percent polymeric color, and antioxidant capacity of processed blackberry products,”Journal of Agricultural and Food Chemistry, 2008; 56: 689-695.
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