Determination of Antioxidant Capacities of Some Dietary Supplements by Spectrophotometric and Chromatographic Methods

Abstract

The main objective of this study is to propose standard analytical methods for the determination and comparison of plant-specific antioxidant components found in some herbal products (sold as dietary supplements). Numerous studies indicate that nutritional supplements can offer medical benefits due to their content of hydrophilic and lipophilic molecules as well as natural extracts or synthetic compounds with antioxidant properties. While these products are marketed as antioxidant boosters, there is a limited amount of data available on the antioxidant activity and bioactive compound content of commercially available formulations. Therefore, in our study, tablet and capsule forms of ground grape seed, rosemary, bitter melon, and ginkgo biloba plants containing polyphenol-type compounds known for their antioxidant properties were investigated. The total polyphenol contents (TPC) of these products were determined by the Folin-Ciocalteu method, and total antioxidant capacities (TACs) were determined by CUPRAC and ABTS methods. The HPLC system was used to detect and quantify the components responsible for antioxidant capacity, and the most appropriate chromatographic analysis methods were suggested for each sample. Total antioxidant capacity values as trolox (TR) equivalent (mmol TR/g) determined by CUPRAC and ABTS methods are 0.90 ± 0.07 and 0.72 ± 0.17 for grape seed, 0.79 ± 0.05 and 0.41 ± 0.09 for rosemary, 0.08 ± 0.006 and 0.11 ± 0.05 for bitter melon, 0.12 ± 0.01 and 0.14 ± 0.02 for ginkgo biloba, respectively. These findings were correlated with HPLC data, and components contributing to the antioxidant capacity were identified.

Keywords

• Dietary supplements
• grape seed
• rosemary
• bitter melon
• ginkgo biloba.

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