Aim: To compare the relative levels of antioxidant activity in vitro in Ginkgo biloba samples (in tablet or capsule form) from different commercial suppliers, to determine whether some brands may be more efficacious in their potential to increase endogenous antioxidant activity, and thereby counter oxidative stress related disorders.
Design: Antioxidant activity of the above sample extracts was determined in vitro against the ABTS.(+) (2-2'-amino-bis-3-ethylbenzthiazoline-6-sulfonic acid) radical, relative to Trolox (water-soluble vitamin E analogue) antioxidant standards, using an established assay procedure.
Outcome measures: The relative antioxidant activity of G. biloba sample extracts was expressed in terms of millimoles per liter of Trolox equivalent (TE) for the initial extract, micromol TE per whole tablet, nmol TE per mg tablet, and nmol TE per mg ginkgo content.
Results: Data (as mean +/- standard deviation (SD) from 4 separate estimations) obtained in this study showed a considerable variation (approximately 50-fold) in the level of antioxidant activity in preparations from different suppliers, particularly when compared on an equivalent (i.e., nmol TE/mg ginkgo) basis. Of the 18 products investigated, the highest level of antioxidant activity (whether expressed as micromol TE per whole tablet or nmol TE/mg ginkgo) was obtained for Pharma Nord Bio-Biloba (Pharma Nord, Morpeth, UK) tablets (p < 0.05, Dunnett's statistical test).
Conclusions: Some of the apparent variation in antioxidant activity of the various products investigated can be accounted for in terms of the physical nature of the G. biloba (i.e., dried leaf powder or standardized concentrated extract) used in tablet formulation. However, even when comparing products based on concentrated extract, the data demonstrated that there is still a considerable variation in antioxidant activity. Presumably this may result from differences in the manufacturing process between suppliers, which in turn may limit the efficacy of these preparations in the prevention or treatment of disease.