Antioxidant Potential of Two Brazilian Seaweeds in Response to Temperature: Pyropia Spiralis (red Alga) and Sargassum Stenophyllum (brown Alga)

Natural antioxidants found in macroalgae represent a significant protective role against oxidative damage. The antioxidant capacity responses to abiotic stresses allow understanding the tolerance and sensitivity of the species. Pyropia and Sargassum inhabiting the intertidal zone exhibit several antioxidant mechanisms against oxidative stress stimulated by environmental factors, such as thermal stress. In this study, we evaluated the antioxidant capacity under different temperatures of the red macroalga Pyropia spiralis and the brown macroalga Sargassum stenophyllum, associated with the composition of mycosporine-like amino acids (MAAs) and phenolic compounds. Antioxidant capacity was determined by four antioxidant assays (ABTS: 2,2-azinobis (3-ethylbenzothiazoline-6-sulfonic acid); DPPH: 2,2-diphenyl-1-picryl-hydrazyl; FRAP: ferric reducing antioxidant power, and metal chelating). Phenolic compounds content was assessed using Folin-Ciocalteau reagent and HPLC, and MAAs using HPLC. In both species, the ABTS assay was the most sensitive antioxidant assay. At low temperature (15 degrees C), P. spiralis exhibited the lowest EC50 (half maximal effective concentration) in the ABTS assay, the highest total antioxidant capacity index, and high content of MAAs (porphyra-334, shinorine, and palythine). For S. stenophyllum, the lowest EC50 value for ABTS assay was registered at 15 degrees C, and the lowest total antioxidant capacity index at 30 degrees C with high content of phlorotannins, probably phloroethols. The information provided by this research may be useful for the study of thermal tolerance and sensitivity in marine macroalgae as well as a template for further investigations of designing phytochemicals in marine macroalgae.