# Chitin and Chitosan in the Alcoholic and Non-Alcoholic Beverage Industry: An Overview
## 2 Chitin and Chitosan Structural Properties  
Chitosan is a natural polysaccharide containing glucosamine and N-acetylglucosamine monomeric units. Chitin is produced by chemical treatments involving the extraction by acid treatment to dissolve the calcium carbonate, named demineralization, followed by the alkaline solution to dissolve proteins, called deproteinization [2; 33]. The chitin extraction could also be performed by biological treatments using enzymes and microorganisms [34], namely proteolytic enzymes to digest the proteins or a fermentation process using microorganisms, which permits digestion of both proteins and minerals [35; 36]. A deodorization process is also frequently performed to eliminate pigments to obtain colorless pure chitin [33]. This process should be adjusted according to the chitin source, due to the diversity in the ultrastructure of the chitin material obtained from the different sources [33]. Chitosan can then be obtained by partial deacetylation of chitin through hydrolysis by a chitin deacetylase [37; 38; 39] or by a chemical procedure [40]. From a chemical point of view, both acids and alkalis can be used to deacetylate chitin; nevertheless, glycosidic bonds are highly vulnerable to an acid; thus, alkali deacetylation is more frequently used [41]. At an industrial scale, deacetylation is usually a nonenzymatic process whereby chitosan is obtained by removing R-NHCOCH\({}_{3}\) residue by treating it with strong alkali (sodium hydroxide solution 40-50%) at high temperatures (100 \({}^{\circ}\)C) [40].  
Deacetylation describes a reaction that removes an acetyl functional group. When the degree of deacetylation (expressed as a molar percentage) is higher than 50 mol%, the biopolymer becomes soluble in acidic aqueous solutions and is called chitosan and behaves as a cationic polyelectrolyte due to the protonation of amine groups in the presence of H\({}^{+}\) ions [42].  
Therefore, chitosan--poly-\(\beta\)-(1,4)-d-glucosamine is a deacetylated cationic linear biopolymer of chitin--poly-\(\beta\)-(1,4)-N-acetyl-d-glucosamine (Figure 1), one of the most abundant natural polysaccharides found in the composition of fungi cell walls [43; 44; 45] and exoskeletons of insects [46; 47; 48; 49], cephalopods, and crustaceans [49; 50; 51; 52; 53; 54]. Chitosan is a linear polysaccharide composed of randomly distributed \(\beta\)-(1-4)-linked d-glucosamine and N-acetyl-d-glucosamine units. The ratio between these two monomeric units, expressed as the degree of acetylation or deacetylation, ranges from 40 to 99% (degree of deacetylation) and the molar weight ranged from 2 to more than 200 kDa [55]. The chitosan functional proprieties are dependent on the structural characteristics, for instance, degree of deacetylation, molecular weight, and purity. Various chitosan are available commercially, which differ primarily in the degree of deacetylation and molecular weight.  
The acetylation degree and molecular weight has been reported to be important chemical characteristics of chitosan, which could significantly influence their proprieties in their several applications [56]. Furthermore, the free amino groups of chitosan are an important characteristic for physical properties, including solubility, chemical properties such as reactivity with other functional groups, and biological properties such as antioxidant and antimicrobial [57].