Antioxidant and free radical scavenging activities of an exopolysaccharide from a probiotic bacterium.

Probiotic bacteria synthesize extracellular polysaccharides (EPSs) with commercially significant physiological and therapeutic activities. This important class of biomolecules is also characterized by their ability to remove reactive oxygen species (ROS) that are formed in the intestine by various metabolic reactions; hence, they exhibit antioxidant activities. Our probiotic bacterium, Bacillus coagulans RK-02, produces an EPS during the exponential and stationary growth phases when grown in a glucose mineral salts medium. The time course of EPS synthesis was studied with respect to biomass growth. The antioxidant and free radical scavenging potential of isolated EPS were studied by various methods, including the beta-carotene-linoleic acid model system, a superoxide radical scavenging assay using the PMS-NADH-nitroblue tetrazolium system, the 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity, a hydroxyl radical scavenging assay using the ascorbic acid-Cu(2+)-cytochrome c system and an in vitro microsome peroxidation inhibition study using a thiobarbituric acid assay. The antioxidant activities were compared to known antioxidants vitamin C and E, which were used as reference standards. The results showed that the EPS, which is a heteropolymer composed of four monosaccharides, produced by B. coagulans RK-02 had significant antioxidant and free radical scavenging activities.