Antioxidant properties of the carotenoid extracts of three Deinococcus–Thermus phylum bacteria, Meiothermus sp. strains RP and TP and Thermus sp. strain YY from Paniphala hot spring, India

Background: The purpose of the study was to extract carotenoids from thermophilic bacteria which show efficient antioxidant and protein oxidation inhibition properties, characterize and identify those isolates, extract the carotenoids in different solvents, quantify the carotenoids and perform concentration-dependent and solventdependent quantitative assays validated and analysed by appropriate statistical tests. Methods: Three pigment-forming thermophilic strains were isolated from water sample of Paniphala hot spring, India, and tentatively identified by 16S ribosomal DNA (rDNA) homology. Different concentrations of the carotenoid extracts (100, 80, 40 and 20 μg) in three solvents, methanol, DMSO and water, were used to determine the antioxidant activity through five methods: the DPPH (1,1-diphenyl-2-picrylhydrazyl) assay, the ABTS (2,2-azino-bis (3ethylbenz-thiazoline-6-sulfonic acid)) assay, the hydrogen peroxide assay, TOC (total antioxidant capacity) assay and inhibition of protein oxidation assay. Statistical analysis of mean, standard deviation, ANOVA and Pearson correlation coefficient was performed in Microsoft Excel statistical package. Results: The isolates were tentatively identified as Meiothermus sp. strain RP, Meiothermus sp. strain TP and Thermus strain YY. Meiothermus sp. formed red coloured pigment, whereas Thermus sp. formed yellow coloured pigment. All of the extracts showed positive results in DPPH assay, ABTS assay and hydrogen peroxide radical scavenging assay with best results obtained when the extracts were dissolved in water. Total antioxidant capacity assay was also high in all the extracts. Protein oxidation inhibition activity was only seen in extracts of strain YY. One-way ANOVA (analysis of variance) clearly showed that choice of solvent influenced the antioxidant capacity of all of the extracts. Conclusions: Newer and efficient antioxidative compounds are constantly being searched for, and the carotenoid extracts of RP, TP and YY have been shown to catalyze various types of antioxidative reactions, including protein oxidation inhibition by YY. Thus, all these extracts have huge potential to be industrially and pharmaceutically useful.