# Marine Bioactives and Their Application in the Food Industry: A Review
## 2 Marine Sources of Bioactive Molecules
### Marine Algae
#### 2.2.1 Macroalgae
Soluble fibers can transfer through the gastrointestinal (GI) tract without digestion, and they can enhance the feeling of satiety due to their bulking capacity [58]. For instance, brown seaweed alginates could involve fecal bulking, water-binding, and reducing transit time in the gut, inhibiting colon cancer. Apart from controlling and maintaining intestinal flora, algal fibers or SPs can act as prebiotics, enhancing the growth promotion of gut microbiota in the GI tract. In particular, SPs obtained from marine algae demonstrate a wide range of bioactivities, including anticoagulant and antioxidant activities. For instance, fucoidan in brown algae (Phaeophyceaeae), ulvan in green algae (Chlorophyceae), and carrageenanan in red algae (Rhodophyceaeae) are the common SPs that showed antioxidant activity [55; 59]. The effectiveness of these polysaccharides in terms of their antioxidant activities primarily depends on factors such as the degree of sulfation, molecular weight, glycosidic bonds, and type of main sugars, among others. Specifically, the antioxidant activity of SPs could be due to the donating ability of hydrogen atoms/electrons to free radicals or chelating transition metal ions (e.g., Cu\({}^{2+}\) and Fe\({}^{2+}\)) since they are extremely nucleophilic [60]. Apart from their antioxidant potential, these polysaccharides, due to their unique structural composition,possess antiproliferative, anticoagulant, antithrombotic, antitumoral, anti-inflammatory, anticomplementary, and antiviral activities (Table 3). In addition to fucoidans, the other storage and structural polysaccharides, such as carrageenan, agar, and alginate, are widely utilized commercial polysaccharides found in macroalgae. They exhibit stabilizing and textural characteristics that are broadly used in the food industry for purposes such as gel formation, thickening, product stabilizing, and the development of water-soluble films [49]. Macroalgae are a significant source of marine-derived proteins, amino acids, and peptides with various biological activities. These proteins are found within cell walls, often in conjunction with enzymes, polysaccharides, and pigments [49]. The composition of protein in macroalgae varies based on factors like species, geographic location, season, and cultivation conditions. Generally, red and green seaweeds contain a higher protein content (9-47%) than brown seaweeds (4-24%). Despite fluctuations in essential amino acid concentrations, research indicates that macroalgae encompass all essential amino acids. The amino acid levels in seaweed are aligned with the dietary protein requirements outlined by the FAO/WHO, suggesting their potential as an alternative protein source [70]. Moreover, seaweed is rich in acidic amino acids like glutamic and aspartic acids but may lack cysteine, tryptophan, lysine, and methionine, which are graded limiting amino acids [49]. For instance, _Palmaria pulmate_ (dulse) is abundant in essential amino acids such as valine, leucine, and methionine, resembling the amino acid composition of ovalbumin. Additionally, the protein content in most seaweeds is substantial, which is akin to that found in terrestrial plants like soybeans [71].