Many chronic and degenerative diseases, such as cancer, Alzheimer, Parkinson and heart disease are partly caused by oxidative stress, caused by free radicals. Antioxidants in foods, such as vitamin C, vitamin E, selenium and many phytochemicals can eliminate these free radicals. There exist different methods to measure the antioxidant capacity of foods and phytochemicals: Oxygen Radical Absorbance Capacity (ORAC), Ferric Ion Reducing Power (FRAP) and Trolox Equivalence Antioxidant Capacity (TEAC).. The most popular method is the ORAC determination, which was developed by the National Institutes of Health in Baltimore. The ORAC method measures the inhibitory effect of the phytochemical on azo-induced oxidation of fluorescein. The fluorescent intensity of fluorescein decreases after the addition of the azo-initiator, which acts as a free radical generator. The degeneration of fluorescein becomes reduced by the presence of antioxidants.
ORAC values of foods
The USDA recommeds an ORAC unit ingestion of about 3000 to 5000 units daily. The ORAC values of a certain food can differ due to growing conditions, processing conditions, analytical procedure and variety. Therefore, the ORAC values (as umol TE/100g) listed below are very indicative! A complete list of ORAC values of food items can be found here
|Sage, fresh leaves||32004|
Limitations of the ORAC method
The ORAC method only measures the degradation of fluorescein but does not identify the free radicals involved. There is also no relationship between ORAC values and the health benefit because other factors are also involved, such as metabolism of the phytochemicals and the absorption into the blood and cells. ORAC values are also overrated by sellers of food supplements, who only advertise the ORAC value without taking into account the real health benefits. Plants also contain beneficial compounds with no ORAC value, such as xanthones, minerals and fibers.