Blue Betadine assay: a safe, low-cost test for antioxidant activity

As part of our commitment to empowering Indigenous youth and promoting broader appreciation of Australian Indigenous peoples’ knowledges, we have developed science activities centred on antioxidant testing of customarily used plants. Conventional antioxidant assays, such as those based on 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric reducing antioxidant power and total phenolic content, often require reagents that are hazardous, costly or difficult to obtain. By contrast, the assay developed here employs safe, low-cost and readily available materials, while providing results comparable to established methods. Based on the redox properties of Betadine (a povidone–iodine complex) and the intense blue colour formed in a starch-Betadine solution, this Blue Betadine Antioxidant Test (BBAT) demonstrated quantitative agreement with the assays listed above for a range of antioxidant compounds (e.g. r2 = 0.989 based on catechin). When applied to extracts from 10 customarily used Australian native plants, the BBAT results were in good agreement with conventional assays, with results most closely aligned with ABTS and DPPH (concordance correlation coefficients ≥0.95). The BBAT is a safe and accessible method suitable for research, education and outreach, providing a culturally relevant platform for exploring the antioxidant properties of customarily used medicinal and food plants.