ORAC

ORAC stands for Oxygen Radical Absorbance Capacity. It is an in vitro assay used to estimate the antioxidant capacity of foods, beverages, and dietary supplements by measuring their ability to scavenge peroxyl radicals generated in a controlled reaction. The typical method uses AAPH as the radical source and fluorescein as a probe; antioxidants in the sample slow the decay of fluorescence. Results are calibrated against Trolox, a water-soluble vitamin E analogue, and reported as micromoles of Trolox equivalents per 100 grams or per serving.

ORAC values have been widely used in nutrition labeling and marketing to compare relative antioxidant strength among foods. However, they measure a specific chemical reaction in a test tube and do not directly predict in vivo effects. The relevance to human health is limited because factors such as bioavailability, metabolism, tissue distribution, and interactions with other nutrients influence whether dietary antioxidants exert meaningful effects.

Criticism and limitations include the use of a single type of radical (peroxyl), variability in assay protocols, and a lack of universal standardization. The complex matrix of foods and the synergistic actions of multiple compounds are not fully captured by the assay, making ORAC values imperfect indicators of overall antioxidant benefit. Consequently, major databases and health agencies have cautioned against using ORAC values to claim health benefits. In 2012 the NIH removed ORAC data from its database, stating that in vitro antioxidant capacity does not reliably translate to in vivo outcomes.

Despite limitations, the ORAC assay remains a tool in research for comparing antioxidant activity under standardized conditions and is often one component among multiple assays used to characterize antioxidant properties.