Functional activity of seaweed extracts from the north portuguese coast

  • Marta Sofia de Almeida Mendes (Student)

Student thesis: Master's Thesis


The use of marine algae as potential sources of pharmaceutical and nutraceutical compounds has been increasing recently, due to the realization that they contain bioactive compounds, with antioxidant and antimicrobial activities (among others), which could inhibit the growth of some contaminant and/or pathogenic bacteria and yeasts, preventing food spoilage or infection and even contributing to its better control. The Portuguese coastline is home to a great diversity in terms of seaweed however, many of them are not yet characterized in terms of functional properties. In this context, the aim of this work was to establish an improved procedure for obtaining extracts from marine algae and to test its antimicrobial activity against selected species of yeasts, Gram positive and Gram negative bacteria. Furthermore, the antioxidant activity of the extracts was also assayed. Finally, an in order to correlate between the composition of the extracts and its bioactivity, their characterization was tentatively established through the determination of lipidic and phenolic profiles. Seaweeds used in this study including those from integrated aquaculture and from their natural habitat, were obtained in the North of Portugal. Gracilaria vermiculophylla was used for the assays of optimization of the extraction procedure, whereas Gracilaria vermiculophylla, Porphyra dioica and Chondrus crispus were used for antimicrobial and antioxidant assays. Optimization studies were focused on the definition of the pre-treatments of the algae (drying) and the temperature used during the extraction process. Results revealed that test organisms were more sensitive to extracts obtained with dried algae, continuously processed at higher temperatures. Subsequently, extracts obtained with three different solvents (ethyl acetate, diethyl ether and methanol:water) were tested. Concerning antimicrobial capacity evaluation, species tested included (i) Gram negative bacteria – Escherichia coli, Salmonella enteritidis and Pseudomonas aeruginosa; (ii) Gram positive bacteria – Listeria innocua, Bacillus cereus, Enterococcus faecalis, Lactobacillus brevis, Staphylococcus aureus, all from food origin and a strain of Staphylococcus aureus from clinical origin and (iii) the yeast Candida spp. from clinical origin as well. Tests to assess the antimicrobial activity of the extracts were performed using the agar diffusion method, and results indicated a stronger antimicrobial activity of the ethyl acetate extracts when comparing with the diethyl ether and methanolic ones, and a weak tendency for inhibition of Gram positive microorganisms. 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), and showed a higher content of fatty acids on aquaculture extracts in Gracilaria vermiculophylla and Porphyra dioica. Taking into account the results for antioxidant activity tested with the ABTS•+ method, it was shown that methanolic extracts had highest activity when compared to the other solvents tested. The phenolic profile revealed that these extracts had highest amounts of phenolic compounds such as catechin and protocatechuic acid, which could take a role in the antioxidant activity.
Date of Award2012
Original languageEnglish
Awarding Institution
  • Universidade Católica Portuguesa
SupervisorAna Maria Gomes (Supervisor) & Ana Carvalho (Co-Supervisor)


  • Mestrado em Microbiologia

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