Effect of extraction method and solvent system on the phenolic content and antioxidant activity of selected macro- and microalgae extracts

The interest in using marine organisms as a source of novel bioactive compounds has increased recently, reinforcing the need to find efficient and cost-effective methods to extract these biocompounds. Thus, the present study has focused on evaluating four solvent systems and three extraction methods to obtain extracts of three macroalgae (Gracilaria sp., Fucus vesiculosus, and Ulva rigida) and two microalgae (Chlorella sp. and Nannochloropsis gaditana). The extracts were evaluated regarding yield, phenolic content, and potential antioxidant activity. Results showed that a lower organic solvent:water ratio increased macroalgae, but not microalgae, biomass extraction efficiency. Levels of total phenolics, ortho-diphenols and flavonoids were highly influenced by algae material and solvent system applied. Strong 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) scavenging activity was obtained with ethanol:water, 80:20 (E80:20) microalgal extracts, while no visible trend was detected for macroalgae extracts. However, methanolic extracts were the most effective in scavenging of 2,2-diphenyl-1-picrylhydrazyl (DPPH). In macroalgae, a high positive correlation was observed between phenolic content and antioxidant capacity while in microalgae, the opposite was verified, suggesting that in microalgae, phenolic compounds are not the main contributors to the observed antioxidant capacity.