# Antioxidant and Antimicrobial Properties of Selected Red Seaweeds from Central Portugal
## 1 Introduction  
Macroalgae are a widely diverse group of photosynthetic organisms, with approximately 15,000 described species [1]. Known as \"seaweeds\" and \"sea vegetables\", marine macroalgae have been exploited throughout the ages, with seaweed harvesting and usage being activities that are deeply rooted into the tradition and history of many cultures, scattered around the world. Eastern cultures have established the use of seaweeds for food and medicine, and consider them to be of great value, and, on a worldwide scale, they have been relied upon in times of warfare, famine and crisis [2; 3; 4; 5; 6]. Among their myriad of uses, around 10,000 are considered edible [7] and can be directly consumed or used in food preparation [7; 8], as their nutritional and nutraceuticalulate has been widely acknowledged [3; 8; 9; 10; 11; 12]. Today, we are fully aware that valuable natural compounds can be obtained from seaweeds, namely phyccolloids, peptides, polysaccharides, polyunsaturated fatty acids, fibers, calcium carbonate, iodine, pigments, diterpenes, phlorotannin's, vitamins and phenols [7; 13; 14; 15; 16; 17; 18; 19]. The abovementioned list includes novel bioactive compounds, which are defined as having a biological interaction or effect when applied to living cells, which depends on the applied [20]. Such seaweed-bound compounds can be extracted and incorporated into the food matrix to create new functional foods [8; 21] or to develop cosmetic, nutraceutical and pharmaceutical products [15; 22; 23; 24; 25; 26; 27; 28]. The bioactive compounds held by seaweeds are responsible for the different bioactivities already acknowledged by many authors. Numerous studies and reviews have referred to the antioxidant [29; 30; 31; 32; 33; 34; 35; 36], antimicrobial [33; 37; 38; 39; 40; 41; 42; 43], anti-fungal [44], anti-inflammatory [29], anti-cholesterol [45; 46], anti-neurodegenerative [47], anti-tumor [48; 41; 49; 32; 41; 45; 44; 46; 47; 48; 49; 50; 51; 52] and prebiotic [53; 54; 14] properties of these bioactive compounds extracted from seaweeds. On industrial and commercial levels, while seaweed bioactives remain relatively unexploited, efforts are being undertaken to promote the use of seaweeds in food ingredient applications [55]. Among the three main groups of macroalgae (the green ones, belonging to the phylum Chlorophyta; the brown ones, from the Phaeophyceae class; and the red ones, from the phylum Rhodophyta), Rhodophyta include some of the most well-known seaweed species, such as _Porphyra_ sp. and _Chondrus crispus_, which are exceptionally popular in Asia [29] and Ireland [56], respectively, especially as an ingredient in their culinary traditions. A number of species have been targeted in several studies, such as _Osmundea pimantifida_ (e.g., [56; 57]), _Spherooccus coronopifolius_ (e.g., [38; 51; 56]) and _Plocamium cartilageu_ (e.g., [35; 50; 58; 59]), and have become quite popular in an academic context. The coralline algae (Corallinales, Rhodophyta) have become fairly popular for bone health, due to their content of calcium (e.g., [60; 61; 62]). However, only the Rhodophyta phylum holds a significantly higher diversity of species, when compared to both Chlorophyta and Phaeophyceae, and many other red seaweeds still require further study. This holds true especially in regions and countries where seaweeds remain highly undervalued, such as Portugal. Portugal holds an incredibly large exclusive maritime zone, with great importance for Portuguese economic development [63], but the remarkable algal abundance and diversity that adorn its shores is still largely unexplored, and the seaweed species remain factually unacknowledged to this day. Therefore, the objective of the present study is to shed light on the antioxidant and antimicrobial activity of twelve red seaweed species commonly found on Portuguese shores.