Avaliação da capacitade antioxidante e identificação e quantificação de compostos fenólicos de sementes e cascas de novos cultivares de girassol (Helianthus annuus L.)

Abstract

Sunflower is considered an oleaginous rich in vitamins, terpenes, aminoacids, carbohydrates, phenolic acids, among others. The presence of these compounds is related to the numerous biological activities assigned to the seed of this plant, including antioxidant activity, as well as action in the prevention of chronic and degenerative diseases. Thus, the objective of this study was to evaluate sunflower seeds and shells of different cultivars, as the antioxidant capacity and the chemical profile. The methanol extracts of sunflower samples were evaluated for their chemical composition (high-performance liquid chromatography - HPLC), content of total phenols, flavones and flavonols and antioxidant capacity (DPPH●, FRAP, lipid peroxidation), and electrochemical tests, using cyclic voltammetry. The total phenolic content ranged from 43.6 to 95.2 mg GAE, while the total content of flavones and flavonols, varied from 4.2 to 47.7 mg EQ. There was also variation in the scavenging activity of radicals (RSA) from 21 to 40.8%, while FRAP values were between 89.7 to 196.9 mg ET/g dry extract. In assays employing biomimetic membranes for evaluation of lipid peroxidation, all extracts (25 ug/mL) showed protection superior to 50%. The quantification of individual compounds, identified by HPLC, was performed by external calibration. It was possible to identify four major components, including chlorogenic acid, caffeic acid, p-coumaric acid and rutin. In the electrochemical study, cyclic voltammograms, on glassy carbon electrode, had shown the presence of peaks with profiles and Epa values similar to those of phenolic acids, such as chlorogenic acid, with a reversible or quasi-reversible electron transfer nature. A determination of the composition revealed a characteristic of important metals, mainly in the antioxidant activity. The extracts also revealed the absence of antiglacial activity, for the proposed method. The results obtained so far and the presence of biologically active phenolic compounds in sunflower samples, demonstrate their potential use for medicinal or nutraceutical purposes.