Analysis of antioxidant capacity and bioactive compounds in marine macroalgal and lichenic extracts using different solvents and evaluation methods

Natural extracts of macroalgae are widely recognized for their antioxidant properties. In this work, the antioxidant capacity of various aqueous and hydroalcoholic extracts obtained from red and green marine algae and from one marine lichen collected from different sites in southern Spain (intertidal and estuarine waters) was evaluated by different methods: ABTS free radical scavenging assay, DPPH assay, and beta-carotene bleaching method (BBM). Contents of total lipids, total carbohydrates, and UV photoprotectors with antioxidant capacity, such as mycosporine-like amino acids and phenolic compounds, were determined. Among the extraction solvents, the highest extraction yield was observed in H2O and 20% MeOH (v/v). The highest antioxidant activity was found in the extracts of the red macroalgae Hydropuntia cornea, Gracilariopsis longissima, Halopithys incurva, and Porphyra umbilicalis, whereas the lowest activity was detected in the green macroalga Ulva rotundata. In general, the antioxidant activity was higher using DPPH than BBM and ABTS. Even so, the ABTS assay is an easy and quick test that provides a comprehensive view of the entire extract in both the lipophilic medium and hydrophilic medium. The antioxidant activity was related to the composition of bioactive compounds and synergistic action is not discarded. The biotechnological use of macroalgal extracts with high antioxidant capacity is discussed.