Comparison of Antioxidant Activity of Commercial Beetroot (Beta vulgaris) Supplements and Beverages Available on the Polish Market

Background: Due to its richness in bioactive compounds and health-promoting properties, beetroot is widely used in dietary supplements available in the form of powder, tablets, capsules, as well as in the form of beetroot juice and beetroot kvass. Methods: In this study, the antioxidant potential of selected beetroot supplements in solid form and beetroot drinks available on the Polish market was compared using ABTS+ and DPPH radical scavenging assays. Total polyphenol content was also determined using the Folin–Ciocalteu colorimetric method. The study material included two products each in powder, capsule, and tablet form, as well as three beetroot juices and three beetroot sourdoughs. Results: Among solid supplements, powders had the highest polyphenol content (up to 12.9 mg GAE/g) and the highest antioxidant potential, while the lowest values were recorded in tablets (4.20 mg GAE/g). When calculated per recommended dose, these differences were even more pronounced (129 mg GAE/dose for powders vs. 0.67 mg GAE/dose for tablets). In the liquid product group, beetroot juices contained significantly more polyphenols than sourdoughs (up to 2828 vs. 230 mg GAE/100 mL) and showed higher antioxidant activity, especially in the DPPH test. Conclusions: Based on the results obtained, it was found that among solid supplements, powders had the highest polyphenol content and the highest antioxidant potential, especially when calculated per recommended dose. In the group of liquid products, juices showed higher antioxidant activity, especially in the DPPH test, compared to beetroot leaven.