Antioxidant activity of fulvic acid: A living matter-derived bioactive compound

Abstract

Fulvic acid (FA) is a class of compound including humic substances together with humic acid and humin. It is formed through the degradation of organic substances by chemical and biological process. FA consists of a mixture of closely related complex aromatic polymers with the presence of aromatic rings, phenolic hydroxyl, ketone carbonyl, quinone carbonyl, carboxyl and alkoxyl groups. The possible application of coal-derived FA as an antimicrobial and anti-inflammatory property has been reported. Actually, it is used as a soil supplement in agriculture and as a human nutritional supplement. In this work, we examined, for the first time, the scavenging activity of biosynthesized fulvic acid in comparison with reference compounds. It was evaluated the in vitro superoxide (O2•-), hypochlorous acid (HOCl), hydrogen peroxide (H2O2), hydroxyl radical (OH•), peroxynitrite (ONOO-) and singlet oxygen (1O2) scavenging capacity of the fulvic acid synthesized from a compost elaborated with poultry manure by spectrophotometric methods. The IC50 (mg/ml) values were as follows: 4.97±0.02, 1.56±0.06, 1.39±0.03, 2.5±0.04, 5.73±0.05 and 3.54±0.03 for O2•-, HOCl, H2O2, OH•, ONOO- and 1O2, respectively. FA displays a scavenging activity compared with the reference compounds although it was less efficient than nordihydroguaiaretic acid (NDGA), ascorbic acid, pyruvate, dimethylthiourea (DMTU), penicillamine and glutathione (GSH) for O2•-, HOCl, H2O2, OH•, ONOO- and 1O2, respectively. The antioxidant properties of the FA partially support the health beneficial properties of this compound; and therefore, the FA is a good candidate to be used in pharmaceutical or food industries as an accessible source of natural antioxidants.