Abstract
Although humic acids (HAs) from peat exhibit various therapeutic properties, there is little information available concerning their physicochemical and antioxidant properties. To address this issue, nine different types of peat, including oligotrophic, mesotrophic, and minerotrophic peat samples, were used for isolation of HA fractions by basic (HAb) and pyrophosphate (HAp) extractions. Physical parameters of the HAs were analyzed by UV-Vis, fluorescent, infrared (IR), and electron paramagnetic resonance (EPR) spectroscopy. Average Mr of the fractions ranged from 17.2 to 39.7 kDa, while their humification index (HIX) varied from 0.49 to 1.21. HAp fractions had a higher content of aromatic structures compared to HAb fractions. Moreover, HAp fractions had a significantly higher content of phenolic OH groups (3.6 ± 0.5 mmol/g) versus HAb (3.1 ± 0.5 mmol/g). All HA fractions exhibited antioxidant activity in radical scavenging and electrochemical assays, and their EPR signal had a single line with g = 2.0035, which is consistent with semiquinone type radicals. Furthermore, the HIX was found to be important in determining the number of semiquinone-type free radicals in the HA structures. Overall, these data provide a molecular basis to explain at least part of the beneficial therapeutic properties of peat-derived HAs.
Highlights
Peat is organic soil formed as a result of incomplete disintegration and humification of marsh plants under high humidity conditions
The nine peat samples analyzed varied in the degree of decomposition from 5–10% to 40–45%, with the ash content ranging from 2.6% (Peat 4) to 16.3% (Peat 7)
The peat-derived humic acids (HAs) fractions represent amorphous dark brown odorless powder, which is highly soluble in water
Summary
Peat is organic soil formed as a result of incomplete disintegration and humification of marsh plants under high humidity conditions. The various anti-inflammatory, immunomodulatory, and radioprotective effects of natural substances seem to be associated, at least in part, with their antioxidant and antiradical effects [17,18,19,20,21]. Antiradical and antioxidant activities of some native humic substances have been reported previously [28,32,33,34], there is no information regarding specific HAs isolated from peat. Because peat could represent an important source of HAs for the pharmaceutical industry, characterization and standardization of their physical and chemical parameters is necessary [35], especially since no clear relationships have been reported between the pharmacological activities of peat-derived HAs and their humification degree, molecular size distribution, or stable-free radical content [36]. We quantified the antioxidant activity of a representative range of peat-derived HA fractions with differing physical and chemical properties
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