Search for bioactive compounds with antioxidant and antibacterial activity in seaweed species from the Portuguese coast

• Autor(a) principal: Marques, Afonso Patrício
• Data de Publicação: 2023
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/161324
• topic: antioxidant activity; antibacterial activity; macroalgae; bioactivity; extraction methods; Domínio/Área Científica::Engenharia e Tecnologia::Outras Engenharias e Tecnologias

The Portuguese coast has an enormous diversity of seaweed species, which offer great potential for the study of bioactive compounds. Of this bioactivity, compounds with antioxi- dant and antibacterial activity are the focus of our work due to their important role in human health. Antioxidant compounds protect against oxidative damage, which can induce cell death, while the antibacterial compounds present in algae can help fight antibiotic-resistant strains. Algae are known to contain molecules that have antibacterial properties. However, these are often left unidentified or only classified in terms of their class. In this work, seven species of algae were selected (based on their abundance and avail- ability on the Portuguese coast) and collected: Chondrus crispus, Codium adhaerens, Codium tomentosum, Cystoseira tamariscifolia, Fucus spiralis, Porphyra umbilicalis and Ulva intesti- nalis for screening bioactive compounds, namely those with antioxidant power and antibacte- rial activity. The samples were collected at “Magoito” beach and “Avencas - Parede” beach (Portugal) during low tide. One of the most important steps in researching bioactive compounds is choosing the most suitable and efficient extraction method(s) for the target compound classes. Therefore, in the first phase, various extraction methods were tested and optimized (e.g. aqueous, meth- anolic, microwave-assisted-extraction (MAE) and Soxhlet). The extracts obtained were then analyzed in a preliminary phase using qualitative phytochemical tests. From this initial screen- ing, a profile was obtained regarding the presence of a series of classes of compounds (e.g. alkaloids, carbohydrates, coumarins, flavonoids, glycosides, phenols, phytosterols, among others). The antioxidant potential of the extracts was then characterized using the FRAP, DPPH and ABTS assays. The results showed variability depending on the type of assay. For instance, in the DPPH assay, a greater antioxidant power was observed in Ulva sp. in extracts obtained through MAE and in C. tamariscifolia in extracts with hexane obtained by Soxhlet. However, in the FRAP assay, C. tamariscifolia showed greater reducing power in methanolic and methanol extracts obtained by Soxhlet extraction, greater than the other species analyzed. Antibacterial activity assays (inhibition zone assay) showed antibacterial activity in ethyl acetate extracts (Soxhlet) in all algae species analyzed. However, in C. tamariscifolia meth- anolic extracts also showed antibacterial activity. Results of the soluble protein content per- formed by Bradford and Lowry assays showed different results, also depending on the extrac- tion procedure. Overall, higher protein content was determined by Lowry method in C. tam- ariscifolia and P. umbilicalis extracts aqueous and MAE, respectively. Regarding the total phe- nolic content, results show that C. tamariscifolia has the highest content in most of the extrac- tion procedures. Moreover, C. tomentosum showed the highest content in lipids. Based on the previous results three seaweed species ( C. tamariscifolia U. intestinalis, P. umbilicalis), were selected for further GC-MS (FAMES and other compounds) and proteomic analyses. The GC- MS analyses identified 18 FAMES in U. intestinalis, 29 in C. tamariscifolia and 23 in P. umbil- icalis. Additionally, Soxhlet extracts allowed to putatively identify several other compounds, some of them related to antioxidant and antibacterial activity but also with anti-inflammatory or anticancer activity, among others. The proteomic results show that most of the proteins identified in the three selected species are mainly related with translation, biosynthetic and metabolic processes. Proteins related to heat shock stress were found in all seaweed species and proteins related to antioxidant activity were also identified in all seaweed species. Therefore, the present work contributes with relevant information regarding the pres- ence of bioactive compounds in algae from the Portuguese coast. The results obtained allow us to select the most promising species to carry out future work in terms of elucidation and purification of compounds of interest to the pharmaceutical or food industry, for example.