Radical scavenging and antioxidant activity of tannic acid

TLDR

Tannic acid is a plant polyphenol consisting of a glucose core esterified with multiple galloyl groups. The study investigates the in‑vitro radical‑scavenging and antioxidant capacity of tannic acid using DPPH, ABTS, ferric‑thiocyanate, Fe3+–Fe2+ reduction, superoxide, hydrogen peroxide, and metal‑chelating assays. These assays were performed and the results were compared against reference antioxidants BHA, BHT, α‑tocopherol, and trolox. Tannic acid inhibited 97.7 % of linoleic‑acid lipid peroxidation at 15 µg mL⁻¹ and displayed strong DPPH, ABTS, superoxide, H₂O₂ scavenging, Fe³⁺‑reducing, and Fe²⁺‑chelating activities, outperforming or matching the reference antioxidants, indicating its potential as a food preservative or nutraceutical.

Abstract

Tannic acid, a naturally occurring plant polyphenol, is composed of a central glucose molecule derivatized at its hydroxyl groups with one or more galloyl residues. In the present paper, we examines the in vitro radical scavenging and antioxidant capacity of tannic acid by using different in vitro analytical methodologies such as 1,1-diphenyl-2-picryl-hydrazyl free radical (DPPH) scavenging, 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging activity, total antioxidant activity determination by ferric thiocyanate, total reducing ability determination using by Fe3+–Fe2+ transformation method, superoxide anion radical scavenging by riboflavin–methionine-illuminate system, hydrogen peroxide scavenging and ferrous ions (Fe2+) chelating activities. Also, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), α-tocopherol and trolox, a water-soluble analogue of tocopherol, were used as the reference antioxidant radical scavenger compounds. Tannic acid inhibited 97.7% lipid peroxidation of linoleic acid emulsion at 15 μg/mL concentration. On the other hand, the above mentioned standard antioxidants indicated an inhibition of 92.2%, 99.6%, 84.6% and 95.6% on peroxidation of linoleic acid emulsion at 45 μg/mL concentration, respectively. In addition, tannic acid had an effective DPPH scavenging, ABTS+ radical scavenging, superoxide anion radical scavenging, hydrogen peroxide scavenging, Fe3+ reducing power and metal chelating on ferrous ions activities. Also, those various antioxidant activities were compared to BHA, BHT, α-tocopherol and trolox as references antioxidant compounds. The present study shows that tannic acid is the effective natural antioxidant component that can be used as food preservative agents or nutraceuticals.