Fucoidan
Fucoidan is an essential as a functional food preventing diseases and encouraging wellbeing, thus exhibiting anti-tumour, immunomodulatory, anti-microbial, hepatoprotective, anti-inflammatory, anti-oxidant and anti-coagulant activities [192]. The heparin cofactor-II inhibits thrombin and factor Xa along with the other factors of coagulation through fucoidan [193]. It was also found to have anti-viral activities by binding to the glycoproteins of the viral envelope and preventing host cell attachment through charge-based interactions [194]. Choie et al. studied macrophages treated with different concentrations of fucoidan (10–100 µg/ml). The macrophages treated with fucoidan were found to exhibit higher anticancer activity by increased phagocytosis, production of lyzosomal enzymes, H2O2, NO radicals, tumor necrosis factor and interleukins [195]. The antioxidant activity of fucoidan extracted from several marine organisms such as F. vesciculosus, P. gymnospora, Dictyota cerviconi, S. vulgare, P. boergesenii, S. cristaefolium, Lobophora variegate, Cystoseira barbata and Dictyopteris delicatula has been studied. Despite different methods of extraction, they were found to scavenge free radicals, possess ferric-reducing potential, reduce hydroxyl mediated DNA damage and have efficient chelating ability [196]. Matsumoto et al. reported fucoidan as an effective treatment strategy for chronic colitis in mice [197]; and the hypothesized mechanism of downregulation in colonic epithelial cells was demonstrated [198]. Fucoidan also activated lipid metabolizing enzymes and stimulating the expression of lipoproteins, thus acting as a barrier against atherosclerosis [199].
3.4.4 Agriculture
Polysaccharides from seaweeds are a source of food among Asia Pacific region. Due to their chemical constituents like alginate, carrageenan and agar, these are commercially important seaweed worth millions of dollars. Alginate and carrageenan are industrially relevant and are extensively studied [200, 201]. Chitosan exhibits antifungal activity as it is able to interrupt fungal growth, by forming a permeable layer/film at the point of interference and simultaneously activating the defense mechanism in plants like accumulation of chitinases, lignification etc. Chitosan treated chili seeds were able to withstand infection better against Colletotrichum sp. with improved results [202]. There are reports about reduced infection in roses and celery against Botrytis cinereal, Peronospora sparsa, Sphaerotheca pannosa and Fusarium oxysporum [203–205]. Also tomato plants were more resistant against Phytopthora infestans due to the presence of chitosan [206, 207]. The effective bioactivity of these polysaccharides relies on their purity and molecular weight [201].
3.5 Conclusions
A broad variety of species are found in the aquatic world, with its abundance of ecosystems. They also produced variations in the basic biomolecules to match their needs and tackle their climate. Among them, polysaccharides are among the most studied and, being essential for the survival and functioning of cells, have the largest diversity; they perform an array of functions ranging from storage to preserving heredity. Additionally, these polysaccharides also have certain useful properties that could be exploited commercially. The two main candidates for research have been cellulose and chitosan. Cellulose, a linear polysaccharide of glucose, has been utilized for tissue repair, biocomposite for wound healing, purification of blood, controlled DNA and drug delivery, gelling agent in food and for blood purification. Chitosan, a cellulose lookalike, has been used for tissue architecture and has multiple applications in food and pharmaceutical industries for its emulsification, anti-oxidant, anti-coagulant, hepatoprotective, and anti-microbial activities. Encapsulation properties of chitosan have been utilized for enzyme entrapment for developing analyte sensors while its adsorbing capabilities have been used for water treatment. Chitosan treatment has been reported to improve resistance of crop plats against pathogens. Alginates have found their major applications in food industry as a food coating agent and emulsion stabilizer, in vivo delivery of peptides and cells, anti-oxidant and bactericidal activities. A niche application also uses its Pb2+ chelating ability to develop special formulations. Alginates are also effective anti-hyperglycemic dietary supplements and promote tissue healing. Carrageenan shows several immunological activities; and the carrageenan gels have shown selective inhibition against many enveloped viruses including HIV, cytomegalovirus and HSV. They are also used for controlled drug delivery through nanoparticle formulations. Its thixotropic properties allow sophisticated foods to be produced quickly. Due to its indigestibility, agar is utilized as a binding agent and in special diet foods; these industries of produce consume 90% of the agar worldwide. Other seaweed polysaccharides such as fucoidans and porphyrans also show similar activities and are consequently, used majorly in the pharmaceutical and nutraceutical industry. Marine polysaccharides constitute a dynamic field, with its derivatizations and structural variations, and concentrated research efforts would be able to better harness the immense biotechnological and commercial potential of these biopolymers.
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