Macroalgae as a Source of Valuable Antimicrobial Compounds: Extraction and Applications

n the last few decades, attention on new natural antimicrobial compounds has arisen due to a change in consumer preferences and the increase in the number of resistant microorganisms. Macroalgae play a special role in the pursuit of new active molecules as they have been traditionally consumed and are known for their chemical and nutritional composition and their biological properties, including antimicrobial activity. Among the bioactive molecules of algae, proteins and peptides, polysaccharides, polyphenols, polyunsaturated fatty acids and pigments can be highlighted. However, for the complete obtaining and incorporation of these molecules, it is essential to achieve easy, profitable and sustainable recovery of these compounds. For this purpose, novel liquid–liquid and solid–liquid extraction techniques have been studied, such as supercritical, ultrasound, microwave, enzymatic, high pressure, accelerated solvent and intensity pulsed electric fields extraction techniques. Moreover, different applications have been proposed for these compounds, such as preservatives in the food or cosmetic industries, as antibiotics in the pharmaceutical industry, as antibiofilm, antifouling, coating in active packaging, prebiotics or in nanoparticles. This review presents the main antimicrobial potential of macroalgae, their specific bioactive compounds and novel green extraction technologies to efficiently extract them, with emphasis on the antibacterial and antifungal data and their applications.The research leading to these results received financial support from Programa de Cooperación Interreg V-A España—Portugal (POCTEP) 2014–2020 (projects Ref. 0181_NANOEATERS_01_E and Ref. 0377_IBERPHENOL_6_E); from MICINN supporting the Ramón and Cajal grant for M.A. Prieto (RYC-2017-22891); from Xunta de Galicia and University of Vigo supporting the pre-doctoral grant of P. García-Oliveira (ED481A-2019/295); by EcoChestnut Project (Erasmus + KA202) supporting the work of M. Carpena and from postdoctoral support for P. Gullón working under the project Bio Based Industries Joint Undertaking (JU) under grant agreement No 888003 UP4HEALTH Project (H2020-BBI-JTI-2019). This work also received financial support from REQUIMTE/LAQV, National Funds (FCT, Fundação para a Ciência e Tecnologia) through project UID/QUI/50006/2019 and by FEDER—Fundo Europeu de Desenvolvimento Regional funds through the COMPETE 2020—Operational Programme for Competitiveness and Internationalisation (POCI), and by Portuguese funds through FCT—Fundação para a Ciência e a Tecnologia in the framework of the project POCI-01-0145-FEDER-030240—PTDC/OCE-ETA/30240/2017.