A Primer on ORAC Mysteries and Weaknesses Part 2 of 3 |
Açaí palms Rowanberries, Finnish summer treats!
[click on this color for Wikipedia links] In this 3-part series, we're looking at the ORAC assay and how it might help us understand the antioxidant value of a food -- just by glancing at a food label ORAC code! Quick review: Every food you eat today contains antioxidants - chemicals in food usually associated with colors or pigments that preliminary science indicates may provide health benefits. Recall our 3-part discussion of The Color Code! The amount of antioxidants in different foods varies mainly on color: the deeper or more varied the color = more pigments = greater antioxidant strength Even foods that are white, like the flesh of a pear or potato, contain antioxidants, although at amounts much lower than in colorful foods.
Science is leading the public toward use of numerical values for antioxidant strength of foods. ORAC (oxygen radical absorbance capacity) is the most commonly used, but there are others with confusing names only to be mentioned here (FRAP or ferric iron-reducing ability in plasma; TRAP or radical trapping antioxidant parameter; TEAC or Trolox equivalence antioxidant capacity; total phenolic content) 2007 Food Industry Discussion on ORAC Strengths and Weaknesses (click) Wikipedia on ORAC Also see the Brunswick link for further background on measuring oxygen radicals, antioxidants and ORAC In Part 1 (click), we covered what the ORAC number actually measures
under development in laboratories around the world. We need this information because the public should not yet accept outright any ORAC value seen on the internet! A better understanding will come from further research.
Mysteries and Weaknesses of ORAC Despite its growing popularity, the ORAC test has measurement problems that are not fully understood even by researchers. In scientific parlance, ORAC is not a “robust” assay, meaning that it bears inconsistencies making interpretation sometimes difficult. There are several possible reasons accounting for this both from the plant food source and the assay itself. As you read the factors below, consider this: When ORAC values are measured for a merlot grape from California vs. one from France, are they going to be the same? 1. Plant genetics. Variability begins in the field. Genetic background of a particular plant food – varying across growing regions that may be geographically adjacent (as in grape vineyards) or distant (as in different continents) – can account for variable levels of antioxidant phytochemicals and ORAC in precisely the same plant specie. 2. Growing conditions. Soil conditions, cultivation methods and pest control, climate exposure, time of plant maturity and harvest, post-harvest handling, storage and processing differences exist, each potentially affecting the phytochemical content and ORAC of any plant food. 3. Environmental stress. Plants may produce more antioxidant phytochemicals (e.g., pigments) in response to chronic stress as a natural defensive mechanism. Under chronic temperature exposure or pest invasion, for example, a berry plant is likely to increase its synthesis of skin and leaf phenolics to protect the fruit, its growth and the seeds. 4. What about organic foods versus those that are pesticide-treated? Plants that are colorful and flavorful, such as berries, attract pests and are susceptible to diseases, requiring most growers to treat their crops with pesticides. Untreated organic crops, however -- vulnerable to attack by pests and predators – would be under this “stress” to produce more defensive antioxidants and so may have higher ORAC scores. 5. Food preparation. As fruits and vegetables may be used fresh from the field, frozen, dried, made into powders or cooked in preparation for consumption, each of these steps influences phytochemical content of plant foods and so alters ORAC.
Freshly picked goji berries Powder made from goji berry juice Photos courtesy of Rich Nature Nutraceutical Labs Above pictures: Do fresh berries and their processed powders have the same ORAC? 6. Inter-assay variation. One of the problems with ORAC discovered by commercial developers of plant food extracts and raw materials suitable for food processing is that the ingredient of interest does not yield the same ORAC score from test to test. Reasons for this variability have not been isolated or published. 7. Old ORAC versus new ORAC (Discussed in Part 1). When ORAC scores were first published for plant foods in the early 2000s, the assay parameters were different than those used now and the resulting scores were consistently lower, sometimes by as much as 10-fold. Some ORAC reports use the old data and others the new. 8. Lack of standard for units of measurement. Scientists have at times used different assay methods with units of measurement that vary from one test to another. ORAC has been reported for 1 cup of fruit, a certain number of ounces, one gram or 100 grams (the usual standard). 9. Different measurements of antioxidant strength. In addition to ORAC are all those other measurements mentioned in small type above, each providing a different unit of antioxidant activity. Each is valid, but this variety of measurement procedures and results creates difficulties in comparing data, both for scientists and the public! These variations in antioxidant determination are no doubt confusing to the public who need a simple numerical result from one reliable test to aid choices of foods with antioxidant qualities. 10. Antioxidant bioavailability. The multitude of antioxidant phytochemicals in plant foods numbers perhaps in the thousands, with moderate differences in chemical makeup accounting for this diversity. In human physiology, however, small changes in chemistry can mean large changes in solubility, acidity, molecular size, permeability across capillary walls, and retention in tissue compartments where the antioxidants can work their benefits. Science has shown, in fact, that anthocyanins from a variety of fruits are not very bioavailable – large amounts consumed are translated only to small amounts absorbed. Recognizing the health value of phytochemicals like anthocyanins, consumers should be encouraged to eat more foods containing these antioxidants, letting nature take its course for absorbing adequate amounts even if the desired antioxidant is not very bioavailable.
Eat a colorful diet! picture courtesy of Berry Wise Inc. Lastly..... 11. Hype!! For developers of fruits, functional foods or ingredients having significant antioxidant strength, the highest ORAC score is desirable, as this characteristic becomes a marketing message. High scores, however, have potential for being abused in marketing campaigns, as developers may obtain several ORAC analyses but use only the highest one in their advertisements. Conclusion 1. ORAC's advantages are that it is relatively simple and inexpensive to run as an assay, a procedure that is likely to improve and become more robust over the next years. ORAC may even be replaced with better techniques. 2. Like any novel consumer item requiring science to unravel its assorted characteristics, the ORAC assay and its interpretation are presently going through a process of working out the bugs. 3. Although this may take a few years to straighten out, ORAC remains a worthwhile index of antioxidant strength that eventually science and consumers will understand, and perhaps even see routinely on food labels! Next! We do a Letterman-like countdown of the top 10 berries with the highest ORAC rankings ~~~~~~~~ Check out the Share this information! http://berrydoctor.com for sign-up Dr. Paul References for The Color Code, paperbacks available at Amazon.com Books * Heber, D. What Color Is Your Diet? ReganBooks, 2001 * Joseph JA, Nadeau DA, Underwood A. The Color Code, Hyperion, 2002. |
