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for Pb²⁺, critical for developing special foods for children with high blood Pb²⁺ content [130]. The gelling ability of alginates is used to make restructured foods, particular from non-appealing ones [131].

       3.4.2.4 Carrageenan

      Carrageenan is used as a gelling agent, due to its excellent heat transfer characteristics. It is used in flan, egg custard, and milk gels. Its thixotropic properties makes it possible to use different layers in the same product; it allows the production of sophisticated food items at a high speed, with smooth and creamy textures [131].

       3.4.2.5 Agar

      Approximately 90% of agar production is for the food industry, with bacteriological and biotechnological uses comprising the rest of the 10%. Agar is primarily a thickening agent; it has a broad gelling ability that restricts its use to 1% of its weight. Consequently, a very small quantity is ingested by humans; due to its indigestibility, agar is also used in special dietary formulations. It is used for confectionary, marmalades, bakery, fruit jellies, and canned products [131].

      3.4.3 Pharmaceutical and Nutraceutical Applications

       3.4.3.1 Cellulose

      Cellulose is also very sensitive to external stimuli. An excellent review on stimuli responsive materials discussed the applications of pH, redox, temperature, light, and mixed stimuli on the controlled release of molecules from cellulose matrices [132]. It also finds applications as DNA delivery vehicles including DNA vaccines [133–136]; cellulose is investigated as suitable agents for oral delivery of DNA [137], which is fraught with complications due to the involvement of the gastro-intestinal tract.

       3.4.3.2 Chitosan

The water-soluble chitosan oligomers generated with chemical, physical or enzymatic hydrolysis were investigated in vitro and/or in vivo as antioxidants. They inhibited myeloperoxidase activity, and preserved DNA and proteins in mouse macrophages from oxidation [138, 139] in myeloid cells. In addition, chitosan has been shown to minimize levels of free fatty acids and malondialdehyde while increased levels of antioxidant enzymes such as glutathione peroxidase (GPX), catalase (CAT) in serum [140]. Microwave-synthesized chitosan oligomers showed scavenging capabilities on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals [141]. Chitosan’s biocompatibility makes it ideal for therapeutic use in vivo [142]. It is also used for subcutaneous, oral, ocular and transdermal drug delivery systems [79]. A chitosan–graphene oxide biocomposite was used as anti-cancer molecule, with superior loading characteristics [143]. Besides, it was also investigated as an agent for buccal, stomach, intestinal and colon-specific drugs being delivered in vivo [144]. In another study, folate conjugated chitosan–graphene oxide nanocomposites were also studied for drug and gene delivery [145]. Vaccines, which are drugs delivered directly to the affected site through injectable formulations, have also been delivered though chitosan based materials [146–148]. For example, Takeuchi et al. have developed chitosan coated, insulin-loaded liposomes to improve insulin absorption through enhanced muco-adhesion, making chitosan an ideal candidate for buccal delivery [149]. It can also be used for nasal vaccine delivery. For instance, a glutamate–chitosan biocomposite can increase transport of insulin in mammals through the nasal mucosa [150]. The presence of chitosan in the vascular system has been shown to improve Th1 immunity, downregulate Th2 immunity and enhance the release of cytokines by macrophages [151]. Modified chitosan inhibited the growth of tumor cells [152], while conjugated chitosan forms were effective against mice lymphocytic leukemia and inhibited the growth of Met-A fibrosarcoma and MH-134Y hepatoma cells [153]. Furthermore, γ-irradiated and cinnamon bark oil incorporated chitosan showed enhanced anti-oxidant activity [154]. A lesser known but equally important application of chitosan is related to its hydrolysis product, glucosamine. Along with chondroitin sulfate, glucosamine is used for the treatment of osteoporosis and arthritis [155].

      The anti-tumor activity of chitosan is also molecular weight dependent; medium molecular weight chitosan was found effective against carcinoma cells. These nanoparticles were found to be acting against S180 and hepatoma 22 (H22) cell lines [156, 157]. In addition, chitosan based materials are investigated as anti-coagulants [158–160], anti-diabetic [161–164], anti-viral [165–167], thrombosis [168], hemostasis [169], and hepatoprotective [170–172] activities. It was interesting to note that, owing to its properties, the same chitosan was used for completely opposite applications: enhancing and dissolving blood clots. Besides, chitosan is also used as an effective flocculating agent for harvesting microalgal biomass [24, 173–176].

       3.4.3.3 Alginate

      Alginate composites are promising agents for in vivo targeted delivery of cells and proteins that promote tissue healing [177] and for their anti-oxidant, and bactericidal activities [178]. Alginates can also be used as anti-hyperglycemic supplements in diets. Addition of a 5 g sodium alginate supplement to test meals led to reduced blood peak glucose and plasma insulin in type II diabetes patients [179]. Due to the porous nature and gelling ability, alginates can be used as controlled protein delivery agents [180].

       3.4.3.4 Carrageenan

Carrageenan has an array of biological activities including anti-coagulants, anti-viruses, immunomodulation, anti-tumors and anti-thrombosis. Among different types, λ-carrageenan shows approximately 2–4 times higher activity compared to non-fractioned and k-carrageenan, respectively. For example, in contrast to k, an enhanced antithrombic activity is likely due to a higher content of sulfur in α-carrageen, was observed. Kindness et al. have provided the activity of carrageenan, that inhibits thrombin by antithrombin-III similar to heparin [181].

      Chondrus crispus derived carrageenan gels have demonstrated a selective inhibition of many human pathogenic viruses [182]. Recent studies suggest their in vitro cancer activity and tumor growth inhibition in vivo [183]. Furthermore, a report has shown that carrageenan promotes immune response against cancer cells by increasing activation of cells [183]. Moreover, the unique properties of carrageenans represent the perfect candidate for controlled and targeted drug delivery systems [184]. They are also extremely amenable to nanoparticle (NP) formulation. Report on the erythropoietin-linked carrageenan nanoparticles prepared using ionotropic gelation process, demonstrated the in vitro controlled release with enhanced encapsulation efficiency [185]. Carrageenan are also considered as transporters in gene delivery process. It was stated that siRNA-primed nanoparticles charged with the required antibodies were dispersed using μ-carrageenan and biodegradable film in the therapeutic prevention of HIV [186].

       3.4.3.5 Porphyran

      Porphyran shows antioxidant, antitumor, immunostimulant, anticoagulant, anti-fatigue, anti-cancer, and anti-microbial activities; it also improves intestinal flora, antibacterial [187]. It is effective against 2,4,6-trinitrochlorobenzene induced contact hypersensitivity by suppressing IgE and interferon-γ (IFN-γ). It also shows inhibitory activity against hyaluronidase, responsible for histamine release from mast cells [188]. Porphyran has immunostimulating activity, raising primary antibody response (IgM) and stimulating macrophages. It can prevent hyperlipidaemia through inhibition of lipid synthesis and decreased apolipoprotein secretion in vivo. This also induces dose-dependent cell death in carcinomas while not detrimental to normal cells [188]. The proliferation of colony and gastric cancer cells was prevented in vitro by pure and crude porphyry extracts [189]. This also decreases phosphorylation in cells of gastric cancer insulin-like growth factor I receptor (IGF-IR) [190]. It also prevents the invasion of Helicobacter pylori; hence, it can be used to prevent or treat gastritis, ulcers and pancreatic cancer. Furthermore, possible mechanisms may be associated with free radical scavenging, increased superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and blood anti-lipid peroxide activities in blood [191].

      

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