4.7 Article

A Systematic Study of the Antioxidant Capacity of Humic Substances against Peroxyl Radicals: Relation to Structure

Journal

POLYMERS
Volume 13, Issue 19, Pages -

Publisher

MDPI
DOI: 10.3390/polym13193262

Keywords

ORAC; humic acids; fulvic acids; carbohydrate; Trametes maxiama; C-13 NMR solution-state spectroscopy; total phenol content

Funding

  1. Russian Science Foundation [20-63-47070]
  2. federal budget of the Russian Federation (CITS) [121041300098-7]
  3. Russian Science Foundation [20-63-47070] Funding Source: Russian Science Foundation

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Humic substances are natural supramolecular systems that have distinct immunomodulatory and protective properties, with their key beneficial biological activity being their antioxidant activity. The antioxidant capacity of these substances depends on both phenolic and non-phenolic moieties in their structure, including carbohydrate fragments.
Humic substances (HS) are natural supramolecular systems of high- and low-molecular-weight compounds with distinct immunomodulatory and protective properties. The key beneficial biological activity of HS is their antioxidant activity. However, systematic studies of the antioxidant activity of HS against biologically relevant peroxyl radicals are still scarce. The main objective of this work was to estimate the antioxidant capacity (AOC) of a broad set of HS widely differing in structure using an oxygen radical absorption capacity (ORAC) assay. For this purpose, 25 samples of soil, peat, coal, and aquatic HS and humic-like substances were characterized using elemental analysis and quantitative C-13 solution-state NMR. The Folin-Ciocalteu method was used to quantify total phenol (TP) content in HS. The determined AOC values varied in the range of 0.31-2.56 mu mol Trolox eqv. mg(-1), which is close to the values for ascorbic acid and vitamin E. Forward stepwise regression was used to reveal the four main factors contributing to the AOC value of HS: atomic C/N ratio, content of O-substituted methine and methoxyl groups, and TP. The results obtained clearly demonstrate the dependence of the AOC of HS on both phenolic and non-phenolic moieties in their structure, including carbohydrate fragments.

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