Biopolymers for Biomedical and Biotechnological Applications. Группа авторов
cruentum inhibited oxidative damage in mouse cells and tissues [41]. Furthermore, the sulfate and uronic acid content, structure, and conformation of the polysaccharide might impact their antioxidant properties [191]. Due to their valuable antioxidant properties, microalgal polysaccharides have a great potential to be used as neuroprotective agents; however, further investigation in the CNS is needed.
2.6.2.5 Other Biological Properties
Microalgal polysaccharides might be useful to treat microbial infections since they can block the adhesion to the host cells and inhibit pathogen growth. In fact, sulfated polysaccharides from microalgae sources inhibited the adhesion of human pathogen Helicobacter pylori and the fish pathogens Vibrio campbellii, Vibrio ordalii, Streptococcus saprophyticus, and Aeromonas veronii [201]. Antimicrobial activity has also been reported for polysaccharides secreted from P. cruentum [45] and A. platensis [60]. EPS from Porphyridium purpureum had antimicrosporidian activity, inhibiting the growth of the honeybee parasite Nosema ceranae [43].
Furthermore, sulfated polysaccharides from macroalgae and marine animals were successful in the inhibition of the enzyme responsible for cholesterol absorption in the intestine, human pancreatic cholesterol esterase. This effect seems to be related to high sulfate content and molecular weight and the presence of 3‐sulfate in the monosaccharide molecule [191]. Thus, microalgal polysaccharides might have an important role in cholesterol regulation. Despite the lack of studies (Table 2.3), both Porphyridium sp. biomass and sEPS had hypocholesterolemic effect, decreasing the accumulation of hepatic cholesterol and lowering the plasma triglycerides and very‐low‐density lipoprotein (VLDL) cholesterol levels in rats fed with high cholesterol diets [38]. Moreover, EPS from P. cruentum had antiglycemic properties and reduced the blood glucose level in diabetic rodents [44].
Sulfated polysaccharides might have a promising future as biolubricants due to their rheological properties. In fact, the sEPS from Porphyridium sp. had a better lubricant effect than the most used lubricant hyaluronic acid, with better results in reducing friction and wear under different simulated joint efforts. These results are related to the great rheological stability over a range of temperatures, pH, and salinities [37]. Furthermore, this sEPS was successfully patented to be a compound in joint‐lubricating products to treat degenerative joint disorders caused by arthritis, due to the promising results demonstrated by injecting the sEPS in joints of rabbits' knees [202].
2.6.3 Commercialization Prospects
The exploitation of microalgal polysaccharides holds great potential of development, representing a sustainable and environmentally friendly strategy to capture CO2 while producing high‐value products with interesting application in therapeutics, cosmetics, and regenerative medicine. However, microalgal polysaccharides had difficulties to enter the market, mainly due to the existence of cheaper alternatives such as macroalgal (e.g. carrageenan, fucoidan, agar) and plant (e.g. guar gum and xanthan gum) products [203]. Nevertheless, there are already some successful examples of the application of microalgal polysaccharides mainly associated with the cosmetic area, such as the sEPS from the red algae Porphyridium sp., marketed by Frutarom under the trade name Alguard™ [6]. Alguard has been used in cosmetics as an antiaging, anti‐irritant, UVB damage protection, anti‐inflammatory, lip balms, healing, and smoothing creams [191]. Also, Algenist™ is a cosmetic product capable of improving health and skin appearance, consisting of a mixture of microalgal polysaccharides named alguronic acid [204]. Furthermore, polysaccharides from microalgae Haematococcus pluvialis and P. cruentum showed antiaging effects, envisaging their use as active ingredients in cosmetic and pharmaceutical formulations [75,205].
2.7 Applications of Chitinous Polymers
2.7.1 Chitin, Chitosan, and Chitinous Polysaccharides
Chitin is the second most abundant polysaccharide available in nature after cellulose. Composed of N‐acetyl‐D‐glucosamine and N‐glucosamine units (Figure 2.5), this polysaccharide can be found on both animal and microbial sources. The chitin extracted from microorganisms is advantageous over the chitin from animal sources, due to several factors: the microbial cultures achieved high growth rates and high cell densities, there is no seasonality of the raw material, the composition of polysaccharide is more stable and controllable, and the microbial chitin is allergen‐free, which is very important in case of pharma/biomedical applications [207].
Figure 2.5 Deacetylation reaction of chitin to chitosan.
Source: Croisier and Jérôme 2013 [206]. Reproduced with permission of Elsevier.
Microbial chitin is a cell‐wall component of several yeast and fungi strains, conferring rigidity and protection to the cells [208,209]. Depending of the fungal source, chitin can achieve a cell‐wall content up to 60% on a dry basis [207]. It is also possible to find chitin polysaccharides in some algae species [210,212].
Fungal chitin can also be found covalently linked to β‐glucans to form chitin complexes such as chitin–glucan complex (CGC) [208,213]. Among the microbial cultures that can be used as chitin/chitinous polysaccharide sources are filamentous fungi (e.g. Aspergillus niger, Aspergillus fumigatus, Rhizopus oryzae, Mucor rouxii) [213,217], mushrooms (e.g. Ganoderma lucidum, Agaricus bisporus, Schizophyllum commune) [218,221], and yeasts (e.g. Saccharomyces cerevisiae, Komagataella (Pichia) pastoris, Candida albicans) [216,222–224]. The chitinous polysaccharide extraction from fungal cell walls can be performed with mechanical and/or nonmechanical methods. Some examples of mechanical methods are high‐pressure homogenization, bead mill, or ultrasound, while the nonmechanical methods include the alkaline hydrolysis (with NaOH or KOH as solvents) or enzymatic treatments [225].
Chitosan is the most known chitin derivative, obtained from the deacetylation reaction of chitin, in high alkali and temperature conditions or by enzymatic hydrolysis (Figure 2.5) [226,228]. Depending on the alkaline treatment performed for fungal cell‐wall lysis, the extraction procedure can also result in the extraction of chitosan or chitosan–glucan complex (ChGC) [215,221,229,230].
2.7.2 Properties of Chitinous Polysaccharides
Chitin is a crystalline and hydrophobic polysaccharide with a molecular weight of 1 to 2 × 105 Da [226,227,231,232]. Chitinous polysaccharides, such as CGC, also have a similar molecular weight (4 to 5 × 105 Da), but since they are covalently linked to β‐glucans, they present an amorphous nature [222]. Chitin and chitinous polysaccharides are insoluble in water and in most of organic solvents. The most common solvent systems used for these biomaterials are N,N‐dimethylacetamide/LiCl, NaOH/urea, LiOH or NaOH at low temperatures, or, more recently, ionic liquids [227,231,233]. In opposition, chitosan is soluble in diluted organic acids such as acetic, formic, or hydrochloric acid solutions [227,231]. Chitosan is also characterized for its high deacetylation degree (DD), usually above 50% and a molecular weight of 2 × 104 to 2 × 105 Da [216,234].
Chitin, chitosan, and their complexes are also known by their biological activity. Behind being biodegradable and biocompatible, these polysaccharides also have antimicrobial, anti‐inflammatory, antioxidant, and antitumoral activity [235,237]. Moreover, fungal chitosan also has emulsifying properties with vegetable oils [214].
2.7.3