Research Article | Volume: 16, Issue: 7, July, 2026
Research Article | Volume: 16, Issue: 7, July, 2026
Antioxidant compounds present in plant-based foods and beverages play a crucial role in preventing oxidative stress by neutralizing reactive oxygen species. This study reports the formation and stabilization of the N,N,N?,N?-tetramethyl-p-phenylenediamine radical cation (TMPD•+) in an aqueous medium and its application as a spectrophotometric probe for total antioxidant capacity (TAC) determination. Unlike the widely used ABTS•+ and DPPH•+ assays, which often require organic solvents, the proposed method operates entirely in water, representing a more environmentally friendly alternative.
The chemical parameters affecting TMPD•+ stability were systematically optimized, including pH, buffer system, solvent effects, and oxidizing agents. The optimal conditions (λmax = 563 nm) were established at pH 5.0 using Fe(III) 1.0 × 10–4 M and TMPD 2.0 × 10–4 M. Standard antioxidants were ranked according to their reducing capacity based on TMPD•+ consumption, with tannic acid and ascorbic acid showing the highest responses. When applied to herbal teas, TAC values expressed as ascorbic acid equivalents showed a strong correlation with the ABTS•+ assay (r = 0.900). These findings demonstrate that stabilized TMPD•+ provides a simple, low-cost, sensitive, and greener approach for TAC determination in plant-based beverages.
Nascimento FFD do, Santos C dos, Oliveira LB, de Moura Domingos LR, Santana WEL, Moya HD. Development and Validation of a Stabilized TMPD•+ Spectrophotometric Assay for Total Antioxidant Capacity in Herbal Teas. J Appl Pharm Sci. 2026;16(7):343-354. https://doi.org/10.1177/22313354261443046
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