Avaliação do potencial antioxidante de macroalgas marinhas do litoral cearense.

Abstract

Seaweeds are sources of a wide variety of beneficial compounds for human. Many of these compounds have antioxidant activity, such as phenolic compounds, carotenoids, and vitamin E. The aim of this research was to evaluate the in vitro antioxidant activity of 50% methanolic extracts from seaweed collected in the coastline of Ceará State, Brazil. The methods used were: DPPH radical scavenging, ferrous ion chelation (FIC), ferric reducing antioxidant power (FRAP), and β-carotene bleaching. In addition to in vitro antioxidant activity, the total phenolic content (TPC) was measured by the Folin-Ciocalteu method, followed by a phytochemical prospecting to point out which are the main classes of compounds present in the algal extracts. The quantification of carotenoids (α- and β-carotene, and lutein) and vitamin E (α- and -tocopherol) was carried out by HPLC. In general, the extracts of brown algae showed the highest ability to scavenger the DPPH radical, the largest FRAP and the highest TPC, followed by extracts of green and red algae. The greatest FIC was observed in red alga extracts, followed by brown and green alga extracts. The high antioxidant activity in β-carotene/linoleic acid model system of green and red alga extracts ranged from 65% to 95%, however it represented less than 40% in brown alga extracts, exception to Padina gymnospora extract which presented activity up to 92%. The majority of the algal extracts analyzed in this study presented activity similar to or even greater than those observed in positive controls (quercetin, BHA, BHT, ascorbic acid, α-tocopherol, β-carotene and EDTA). Fenols were detected in brown algae only; anthocyanins, anthocyanidins, chacons, aurons and leucoanthocyanins were observed in some species of Rhodophyta Phylum. All the other classes of phenolic compounds were found in at least one species within each Phylum, exception to flavononols which have not been detected in green alga extracts. TPC was the main responsible for the ability to scavenger the DPPH radical, FIC and FRAP in green and red algae. On the other hand, in brown algae TCP was influenced only by FRAP. All extracts of green, red and brown algae exhibited the presence of β-carotene and lutein. The latter was the major carotenoid within Chlorophyta and Rhodophyta. Naturally absent in brown algae, α-carotene was not detected in five species of Chlorophyta and Rhodophyta algae. α-Tocopherol was determined in all species, except Ulva fasciata and U. lactuca extracts. The isomer δ-tocopherol was quantified in eleven out of twenty-three alga species. Antioxidant activity and levels of compounds in the algal extracts were different, but all of them showed antioxidant potential.