3.1.1. Role of Polysaccharides in Medicine

Algal polysaccharides differ from those found in terrestrial plants because they include unique poly-uronides, some of which are pyruvylated, methylated, sulfated, or acetylated. Sulfated polysaccharides including fucan sulfate, ulvan, and carrageenan have received the

most interest because of their biological features [29]. Some of polysaccharide's structures are presented in Figure 3. Sulfated polysaccharides (SPS) are found in edible seaweeds such as ulvan (Chlorophyta), fucoidan (Phaeophyta), or carrageenan (Rhodophyta), and have numerous applications in pharmaceutical, nutraceutical, and cosmeceutical sectors. Antioxidant, anticancer, anti-inflammatory, anti-diabetic, anticoagulant, immunomodulatory, or anti-HIV activities have been discovered in SPS. The interaction between polysaccharide or intestinal microbes is widely credited with these actions, indicating functional or therapeutic feature of sulfated polysaccharides [30]. In most circumstances, smaller molecular weight SPS has more antioxidant activity than high molecular weight SPS because proton donor action occurs in cells in low molecular weight SPS. Furthermore, this antioxidant property is vital in preventing generation of free radicals in cell, which prevents oxidative cell wall damage [31]. The antigenotoxic property of alginate oligosaccharide in form of nanocomposites extracted from brown alga has received significant attention [32]. Table 1 shows some of the activities and qualities of polysaccharides from seaweeds that are useful as antioxidants and anticancer agents.

**Figure 3.** Chemical structures of different types of polysaccharides in seaweeds.


**Table 1.** Seaweeds polysaccharides and their roles in medicine.

Carrageenans are polysaccharides present in cell walls of red algae that are classified into three categories based on their sulfation level: iota, kappa, or lambda [41]. Carrageenans, galactan, or xylomannan sulfates discovered in red seaweeds have antimicrobial effects that prevent viruses from interacting with cells by inhibiting the formation of structurally similar complexes [42]. Carrageenans derived from Hypnea spp. (including green alga *Ulva lactuca*) have antioxidant and antiviral characteristics, as well as strong hypocholesterolemic capabilities, by lowering cholesterol or sodium uptake whereas raising potassium absorption [43]. Agar is polysaccharide made up of agaropectin or agarose, which are both derived from red seaweeds and have structural or functional characteristics that are comparable to carrageenans [41]. Porphyran, a polysaccharide produced from red Porphyra spp., was shown to have anticancer, immunoregulatory, and antioxidant effects [44].

Sulfated polysaccharides such as galactose, glucose, rhamnose, glucuronic acid, or arabinose isolated from the microalgae *Spirulina platensis*, as well as those speculated from red algae *Gracilariopsis lemaneiformis* (i.e., 3,6-anhydro-l-galactose or d-galactose) demonstrated antiviral and antitumor action [44]. Fucoidan polysaccharides, usually manufactured by brown algae, such as *Ascophyllum nodosum*, *Laminaria japonica*, *Viz fucusvesiculosus*, *Fucus evanescens*, *Sargassum thunbergi*, or *Laminaria cichorioides*, were shown to reduce blood cholesterol levels and deter metabolic syndrome [43]. Antiproliferative, antiviral, anti-peptic, antioxidant, anticanceranti-coagulant, antithrombotic, anti-inflammatory, or antiadhesive characteristics are all found in algae fucoidans. They also have potent anticancer properties or can prevent lung cancer metastasis through hindering matrix metalloproteinases (MMPs) or Vascular Endothelial Growth Factor (VEGF) [45]. Fucoidans may have a synergistic impact on currently used anticancer drugs [46]. To improve the efficacy of existing conventional treatments, these polysaccharides can be added into or mixed with them. *Caulerpa lentilifera*, *Eucheuma cottonii*, *Ahnfeltiopsis concinna*, *Chondrus ocellatus*, *Sargassum polycystum*, *Ulva fasciata*, *Gayralia oxysperma*, or *Sargassum obtusifolium* soluble dietary fibers have been found to prevent metabolic syndrome or lower blood cholesterol levels [43].

Alginate (β-d-mannuronic acid, α-l-guluronic acid, d-guluronic, or d-mannuronic) is non-sulfated polysaccharide isolated from dark brown seaweed *Laminaria digitata* that is commercially accessible (in acid and salt forms) [41]. Alginates isolated from brown have a nutritional function or are beneficial to gut health, donating to water binding, fecal bulking, or reduction in colon transfer time that is an important indicator through colon cancer prevention, according to previous studies [47]. Furthermore, because of their binding nature, alginates alter mineral bioabsorption, aid in maintaining body weight, discourage overweight and obesity, and lower hypertension [41].

#### 3.1.2. Role of Polysaccharides in Food Industry

While the global market for healthy ingredients expands, there is significant interest in the identification of new functional food ingredients from various natural sources [48]. As a result, the prospect of employing algae-derived molecules to create novel functional food products has piqued the interest of many people in recent years. The largest and most often used hydrocolloids from marine algae in the food industry include agars, alginates, and carrageenans, as illustrated in Table 2.

**Table 2.** Seaweeds polysaccharides and their roles in foods and cosmeceuticals.


Agar is a type of phycocolloid formed of agarose (a linear polysaccharide) and a heterogeneous combination of smaller molecules (agaropectin). Agar is a widely recommended food additive in the USA and in Europe (E406), and cannot be digested into the gastrointestinal system in humans due to the lack of α/β-agarases [57]. Furthermore, gut bacteria can convert it to d-galactose [58]. At low doses, agar is an excellent gelling agent, capable of forming a brittle, stiff, and thermally reversible gel [59].

Surprisingly, agarose is the primary gelling agent in agar. In this manner, hydrogen bonding between nearby D-galactose and 3,6-anhydro-L-galactose create agar gel along its linear chains of agarose with repeating units. The food sector uses 90% of the agar produced for its gellifying characteristics. It is used as a gelling agent in the culinary, food, and confectionery sectors to produce Asian traditional foods, canned meats, confectionery jellies, and aerated items such as marshmallows, nougat, and toffees [60]. Agar is commonly used as a food additive in the production of dishes that require warming before consumption, such as cake, sausage, roast pig, and bacon [61]. Agar fluid gels can be used to make foams with excellent stability to replace fat in whipped desserts [61].

Alginates, such as agar, are commonly used in the food manufactures for gelling, thickening, stabilizing, and film formation. In contrast to other hydrocolloids, alginates are unique in their cold solubility, allowing the creation of heat/temperature-independent non-melting gels, cold-setting gels, and freeze–thaw-stable gels [62].

Carrageenan is commonly used in dairy products such as cheese and chocolate milk to provide thickening, gelling, stabilizing, and strong protein-binding characteristics [63]. Carrageenan was used in dairy products at low doses due to its exceptional ability to link milk proteins. This hydrocolloid was capable of keeping milk solids suspended and therefore stabilize them. The meat industry is another area where carrageenan (mostly manufactured by Eu-cheuma) is used. It is commonly used in the manufacture of hamburgers, ham, seafood, and poultry preparations, due to its water retention properties. Carrageenan is also found in aqueous gels such jelly, fruit gels, juices, and marmalade [61]. Carrageenans, as cryoprotecting agents, play an important role in the structural and textural stability of frozen foods. Additionally, k-carrageenan was used as a supplementary stabilizer in an ice cream mix [64].
