Multi-Method Screening of Commercial Antioxidant Supplements: Antioxidant Activity and Selected Antioxidant Compound...

Daily diets may not always provide adequate amounts of antioxidants for some individuals, prompting a growing interest in dietary antioxidant supplements. This study focuses on a diverse range of supplements marketed as "antioxidant supplements" in the Polish market, encompassing both single-ingredient and multi-component formulations. The objective of this study was to assess the antioxidant activity and polyphenolic profiles of these supplements to provide comparative insights. A total of 96 supplements from various manufacturers were analyzed. Polyphenol content was determined using the Folin-Ciocalteu method, while antioxidant activity was evaluated using three approaches: FRAP, DPPH, and electrochemical assays, together with HPLC-based profiling of selected antioxidant compounds. Total polyphenol content ranged from 0.146 to 177.499 mg GAE/g. Antioxidant activity showed broad dispersion across products, with FRAP values from 0.027 to 64.734 mmol/g, DPPH from 0.013 to 22.499 mmol Trolox/g, and electrochemical response from 51.162 to 374 µC. FRAP and DPPH were strongly correlated with each other (Spearman ρ ≈ 0.68) and with total polyphenols (ρ ≈ 0.89 and 0.84, respectively). Electrochemical response showed moderate correlation with total polyphenols (ρ ≈ 0.63). Moderate positive correlations were observed between assay responses and rutin, quercetin, resveratrol, ferulic acid, and chlorogenic acid. Compound profiles differed between supplement source groups and were highly heterogeneous in multi-component formulations. The results indicate that antioxidant activity is associated with compound composition and distribution rather than total polyphenol content alone and support the use of multiple complementary assays for supplement evaluation.