Antioxidant and anti-norovirus properties of aqueous acetic acid macromolecular extracts of edible brown macroalgae

Previous studies reported the activity of fucoidans and polyphenols (phlorotannins) extracted from brown algae against enveloped viruses. The aim of this study was to investigate the effects of brown macroalgae on the non-enveloped norovirus. Aqueous acetic acid macromolecular (>3 kDa) extracts (AAEs) were obtained from ten samples of eight brown macroalgal species. Saccharides and sulphate composition, weight-averaged molecular weight, and total phenolic content (TPC) of the AAEs were measured to estimate their fucoidan and polyphenol content. Murine RAW264.7 macrophage cells and the human norovirus surrogate murine norovirus-1 (MNV-1) were used for the anti-norovirus assay. One hour of direct exposure to TPC-rich AAEs from Sargassum horneri (Sh), Eisenia bicyclis (Eb), Cladosiphon okamuranus (Co), and Undaria pinnatifida inactivated MNV-1. In contrast, pre-treatment of RAW264.7 cells for 20 h with AAEs from another U. pinnatifida sample, Analipus japonicus, and Co protected RAW264.7 cells against MNV-1 infection. The AAEs from Co contained high TPC and sulphated fucans (fucoidans) might be the most promising anti-norovirus agents as they directly inactivated MNV-1 and protected RAW264.7 cells from it. The AAEs of phlorotannin-rich Sh and Eb are also potentially effective at direct inactivating MNV-1.