Phenolic content and antioxidant activity of fractions obtained from selected Irish macroalgae species (Laminaria digitata, Fucus serratus, Gracilaria gracilis and Codium fragile)

Total phenolic content (TPC) and antioxidant activity of crude and enriched aqueous, ethanol/water and methanol/water extracts from four species of Irish macroalgae Laminaria digitata, Fucus serratus, Gracilaria gracilis and Codium fragile were assessed. The antioxidant activity and TPC of crude and enriched extracts were assessed using the DPPH, FRAP and Folin-Ciocalteu assays. Extracts of F. serratus were significantly higher (p < 0.05) than the other macroalgae. Further enrichment based on liquid-liquid extraction and molecular weight cut-off (MWCO) dialysis generated fractions of low and high molecular weights, (< 3.5 kDa, 3.5–100 kDa, >100 kDa) and hydrophobic with a significant increase in antioxidant activity and TPC (p < 0.05) compared to the crude extracts. Initial weak activity in the <3.5-kDa fractions for the species F. serratus was enhanced following reverse-phase flash chromatography fractionation. Analysis by quadrupole time-of-flight mass spectrometry (Q-Tof-MS) suggests that the <3.5-kDa fractions for F. serratus contained a high abundance of low-molecular weight phlorotannins. This study highlights techniques to further enrich fractions with potential for further exploitation, in particular F. serratus.