A comparative assessment of the activity and structure of phlorotannins from the brown seaweed Carpophyllum flexuosum

The extraction and antioxidant activity of phlorotannins from the brown seaweeds Carpophyllum flexuosum, Carpophyllum plumosum and Ecklonia radiata was investigated to identify an optimised extraction process for novel anti-oxidant extracts. Subsequently, the composition of the most active phlorotannin extracts was determined. Microwave assisted extraction (MAE) using water was the most efficient extraction process with shorter processing times and a higher purity product than obtained with any of the other methods tested. MAE resulted in the fast, effective decomposition of the cellular structure, as identified through scanning electron microscopy (SEM), and this related directly to the efficiency of extraction. Phlorotannins extracted from C. flexuosum by MAE had the strongest antioxidant activity (62.1 mg gallic acid equivalents (GAE)/g dw of seaweed) and more than 5.5-fold greater 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging ability than ascorbic acid after 7-day incubation periods at 30 °C and at 60 °C. Six major chemical species of phlorotannin, belonging to the fuhalol group, were identified within the MAE extract using NMR and HPLC-MS. The results confirm phlorotannins from C. flexuosum to be promising natural, bio-derived and bio-compatible antioxidants, while identifying the most effective method to extract the constituents and retain antioxidant activity.