# Marine Bioactives and Their Application in the Food Industry: A Review
## 2 Marine Sources of Bioactive Molecules
### Marine Algae
#### 2.2.1 Macroalgae  
Seaweeds are well known for their abundance of dietary fiber, polysaccharides, proteins, lipids, minerals, and vitamins, as well as other phytochemicals. Furthermore, they encompass a range of bioactive compounds, including phenolic compounds, known for their antibacterial, antiviral, antifungal, anticancer, and antioxidant functions [50]. Owing to their diverse biological activities, they have gained increasing interest as a promising source of pharmaceutical products and functional food ingredients. Due to their functional and health-beneficial properties, most East Asian consumers incorporate seaweeds into their cuisine as a functional food ingredient. On the other hand, microalgae are microscopicorganisms (around 20 \(\upmu\)m) and are frequently characterized as phytoplankton, including diatoms (phylum Ochrophyta, class Bacillariophyceaeae), dinoflagellates (phylum Myzzozoa, class Dinophyceae), blue-green algae (phylum Cyanobacteria, class Cyanophyceaeae), and green and yellow-brown flagellates such as pyrmesiophyta, prasinophyta, chlorophylla, and cryptophyta, among others [51; 52]. Among them, Nostoc, Arthospira (Spirulina), edible blue-green algae, and Aphanizomenon are very common species that have been used for centuries [53]. They have a rich profile of PUFAs, polysaccharides, carotenoids, and chlorophyll pigments, which have been used in the food and pharmaceutical sectors. For example, _Dunialella salina_ is a rich source of vitamin A and PUFAs and is cultured on a commercial scale [54]. Macroalgae Polysaccharides  
Seaweed is a rich source of polysaccharides, mainly SPs, which demonstrate strong biological and physicochemical characteristics, suggesting their potential to be used in different sectors, including food production. A wide range of polysaccharides have been identified in seaweed, mainly observed as storage polysaccharides and in cell wall structures. The primary components of cell wall polysaccharides consist of hemicelluloses, cellulose, and neutral polysaccharides, which serve to impart structural strength to the thallus when submerged in water. For instance, polysaccharides in brown algae consist of laminarin (\(\beta\)-1,3 glucan), fucoidan (sulfated fucose), cellulose, sargassan, alginates, and mannitol, while green algae contain sulfated galactan, SPs, and xylans. Moreover, red algal polysaccharides are mostly carrageenanans, water-soluble sulfated galactan, agars, xylans, floridean starch (amylopectin-like glucan), and porphyrin [19; 55; 50]. In particular, polysaccharides with sulfated hemi-ester groups linked to sugar moieties are observed as galactan (agar and carrageenanan) in red algae (Rhodophyceaeae), fucoidan (fucoidans, ascophyllan, and sargassum) in brown algae (Phaeophyceaeae), and arabinogalactans with a lesser content of sugars in green algae (Chlorophyceae) [7; 19; 56]. Generally, SPs can be categorized into three distinct groups such as water-soluble ulvan found in green algae (which consists of sulfated aldobiuronic acid and sulfated rhamnose), linear carrageenan and galactan found in red algae, and water-soluble fucoidan found in brown algae (xylose, uronic acid, fucose, and galactose) [19; 56]. The percentage of polysaccharides in seaweed species can go up to 75% on a dry weight basis, while green seaweeds, mainly Ulva, contain a high level of polysaccharides [53]. For example, _U. lactuca_ contains over 80% polysaccharides, mainly ulvan, a functional, structural, and storage polysaccharide [57]. Most of these polysaccharides are mainly dietary fibers, which promote gut health by maintaining the intestinal environment, and the total fiber content of seaweed can vary between 29 and 62% [55]. These dietary fibers can be categorized into two groups: water-soluble, namely alginic acid, agars, porphyrin, furanan, and laminaran, and insoluble dietary fibers, such as mannans, cellulose, and xylan.