Antimicrobial activity and lipid profile of seaweed extracts from the North Portuguese Coast

Seaweeds or marine macroalgae are a potential renewable resource in the marine environment and can represent a source of new natural compounds for human nutrition. This experimental work focused on the selection of a suitable extraction method, using Gracilaria vermiculophylla as a model, followed by the characterization of the antimicrobial activity of different solvent extracts of Gracilaria vermiculophylla, Porphyra dioica and Chondrus crispus, both from wild and from an integrated multi-trophic aquaculture system (IMTA), collected in the north of Portugal. Additionally, the fatty acid profile of the seaweed extracts was also investigated. Extraction tests included the definition of the physical state of the seaweed, temperature and type of solvents to be used during the process. Results revealed that test organisms (Gram negative and Gram positive bacteria as well as one yeast species) were more sensitive to extracts obtained with dried algae, processed continuously at higher temperatures. Results from antimicrobial activity of wild and IMTA seaweed extracts showed stronger antimicrobial activity in extracts of ethyl acetate when compared with those from methanol and diethyl ether; furthermore, among the type of microorganisms tested, there was tendency for inhibition of the Gram positive ones. In general, there appears to be a higher antimicrobial activity for the microorganisms under study in extracts obtained from aquaculture species, when compared with the wild ones. The fatty acid profile of ethyl acetate extracts revealed a predominance of saturated fatty acids (SFA), especially palmitic acid (16:0), followed by polyunsaturated fatty acids (PUFA) and monounsaturated fatty acids (MUFA). A higher content of fatty acids in aquaculture extracts of Gracilaria vermiculophylla and Porphyra dioica was also observed.