Abstract:

Abstract The extracts of the algae species Scenedesmus obliquus isolated from Kapulukaya Reservoir (Kırıkkale, Turkey) were analyzed to determine the composition, content and antioxidant properties of carotenoids. The HPLC analysis was applied to identify carotenoids species and to determine their contents. Methanol–acetonitrile–water (84:14:2, v/v/v) and methylene chloride (100%) used in the gradient solvent system resulted in an acceptable separation. Of the 22 resolution peaks assigned to carotenoids either tentatively or positively, the first eight were identified to be epoxy containing while the remaining ones as main carotenoids namely, all-trans forms of lutein, β-carotene, α carotene, zeaxanthin, 13-or 13’-cis-lutein, 9-or 9’-cis-lutein, cis-lutein, 13-or 13’-cis- β-Carotene, 9-or 9’-cis-β-Carotene, 9-or 9’-cis- α-carotene and cis-neoxanthin. Quantitatively, S. obliquus was predominated by all-trans isomers of lutein and β-carotene, being 83.74 % (2.52 mg g-1) in total carotenoids (TC). Antioxidant capacity assays of DPPH and FRAP showed considerably low effects of S. obliquus extracts compared to standards. This was attributed to the lesser existence of cis isomers within derivatives. Multiple regression was utilised to partition the antioxidant effect of both assays and, revealed an estimation of FRAP dominating over DPPH. A need was arisen on the exploration of isomerisation mechanisms of the carotenoids compounds in order to better evaluate the species for a probable potential of further practical applications.

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