Microalgae of different phyla display antioxidant, metal chelating and acetylcholinesterase inhibitory activities

► Hexane extracts had the highest antiradical Fe2+-chelating activities. ► Chlorella minutissima, Tetraselmis chuii and Rhodomonas salina exhibit strong anti-AChE properties. ► Polyunsaturated fatty acids and sterols are the main compounds in bioactive extracts. ► The species under study are a valuable source of antioxidants, metal chelators and AChE inhibitors. ► This is the first study on chelating and AChE inhibitory activities in microalgal species. Methanol and hexane extracts from Tetraselmis chuii, Nannochloropsis oculata, Chlorella minutissima and Rhodomonas salina were evaluated for total phenolic contents, radical scavenging activity (RSA), metal chelating potential against copper and iron ions and acetylcholinesterase (AChE) inhibition. Only the methanol extracts contained phenolic compounds. The hexane extracts had the highest RSA. The extracts had a higher capacity to chelate Fe2+ ions, more pronounced in the lowest concentration of the hexane extracts with values ranging from 73.3±3.3% (R. salina) to 97.5±1.1% (N. oculata). The highest AChE inhibitory activity was found in the hexane extracts at 10mg/ml of C. minutissima (79.3±1.9%), T. chuii (85.7±0.7%) and R. salina (81.5±7.5%). GC–MS analysis indicated polyunsaturated fatty acids and steroids as the most abundant compounds in the hexane extracts. The species under study provide a valuable source of antioxidants, metal chelators and AChE inhibitors.