Impact of environmental conditions on the composition and properties of algae

Abstract

The following algae species collected from Las Canteras beach (Gran Canaria) arrivals between June and August in the summer of 2021 were studied in terms of their carbohydrates and malondialdehyde contents, and antioxidant activities (measured through the radical scavenging activity and ferric reducing power assays): Cymopolia barbata, Caulerpa prolifera, Lobophora variegata, Dictyota dichotoma, Dictyota fasciola, Sargassum vulgare, and Hypnea spinella. Their content in free carbohydrates (in mg g-1 of dry algal biomass) ranged from 0.02 in Dictyota fasciola to 7.64 in Lobophora variegata and from 3.68 in Dictyota fasciola to 10.09 in Cymopolia barbata for total carbohydrates. Caulerpa prolifera, Sargassum vulgare and Cymopolia barbata extracts were the most active in inhibiting 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) (71.84, 75.09 and 79.60% respectively) and showed low levels of malondialdehyde (MDA) (7.02, 5.62 and 4.93 mmol g-1 respectively). Cymopolia barbata also showed the highest capacity of reducing iron (0.112 mmol of iron (III) g-1 of algae). These results confirm the potential possibilities of the arriving algal biomass as a new sustainable source of raw material with nutritional, functional, and/or biomedical properties. The seasonal variation in composition and antioxidant activities of samples of the two more abundant species in the arriving algae (Cymopolia barbata and Lobophora variegata) collected in January, April, August, and November were also evaluated. Phenolic compounds gallic acid, epicatechin and syringic acid were found in both algae, but Cymopolia barbata showed considerably higher concentrations as well as higher radical scavenging activity with a maximum in August (79.69%). Samples of seawater enriched with exudates from coccolithophore Emiliania huxleyi were studied to improve the understanding of the extracellular release of organic ligands under future marine acidification scenarios. Cultures of Emiliania huxleyi were grown under different pH conditions (7.75, 7.9, 8.1 and 8.25). The highest amounts of exuded phenolic compounds (5.04 μg L-1 and 3.47 μg L-1) were observed in cultures with lower cell densities (9.15×107 at pH 7.75 and 9.98×107 at pH 8.25, respectively), indicating that these cells exuded higher amounts of phenolic compounds (55.1 and 34.7 fg cell-1respectively).