# Shellfish Chitosan Potential in Wine Clarification
## 1 Introduction  
Chitin is the most abundant polysaccharide on earth after cellulose. Chitin is composed of 2-acetamido-2-deoxy-b-D-glucose (N-acetylglucosamine) units linked by \(\beta\) (1-\(\pm\)4) bounds, and it is organized in layers of polysaccharide sheets. The sheets are composed of multiple parallel chitosan chains that could assume three different crystalline forms (\(\alpha\), \(\beta\), \(\gamma\)). However, chitin is synthesized by a large number of living organisms, such as arthropods and insects (exoskeletons); crustacean (shells); and algae, plants, and fungi (cell walls) [1], mainly in its \(\alpha\)-form, i.e., it is organized in parallel chitin chains structured in an anti-parallel sheet. In contrast, \(\beta\)-chitin, composed of chitin chains arranged in a parallel sheet, and \(\gamma\)-chitin, a mixture of the previous two forms, are quite rare. For the extraction of chitin and its derivatives at the industrial scale, two principal sources of \(\alpha\)-chitin are suitable, such as shellfish and fungi. Annually, the seafood industry produces about 106 tons of waste [2], most of which is destined to composing or to the conversion into low-value products, namely animal feed or fertilizers [1]. As an alternative, by-products such as the shellfish shell could be directed to the component recovery, and chitosan (the deacetylated form of chitin, CTS) represents one of the best possibilities for their re-qualification. Concerning that, approximately 2000 tons of chitosan is produced every year, and its principal sources of extraction are shrimp and crab shell residues [1]. Besides, fungi represent an alternative abundant source of chitin and chitosan that could be extracted from both mycelium and spores [3]. [PERSON] and [PERSON] [3] reported the first attempts to begin a multiple added-value compound production from fungi thatinvolves chitin and other compounds. It was estimated that more than 60% of the biotech industries use fungi in different processes such as brewing and baking, as well as food, antibiotics, pharmaceuticals, organic acid, and enzyme production, and that only for citric acid production, _Aspergillus niger_ cultivation results in an annual waste of \(\sim\)80 kton of mycelium [4]. In the choice of the source, it should be considered that the chitin structure, its percentage, and purity vary in reason of the anatomical structure in which it is located. As an example, the exoskeleton of shellfish is composed of chitin (20-30% _w/w_), proteins (20-40% _w/w_), minerals (30-60% _w/w_) [2], and by pigments and lipid in traces [5]. Insects, instead, present chitin both in the exoskeleton and in the inner parts, such as the tracheal system, that contain catecholamines -0-quinones allowing cross-linking between protein and chitin (36-62% _w/w_ dry weight of chitin [2]). Instead, the fungal cellular wall consists of chitin (15 to 18%), \(\beta\)-glucans (37%), lipids (19%), and several other sugars (8 to 15%, Figure 1) [6]. However, it was demonstrated that these percentages could vary among species and life stage [7]. Chitin isolation from natural material follows three steps that are different between fungal and animal CTS: the first step--which could be called \"pre-treatment\"--consists of the raw material washing, drying, and smashing. In the case of shellfish, in this step the minerals are removed by an acid washing, natural pigments are eliminated by means of organic or inorganic solvents, while an alkaline wash is used to remove proteins, glycoproteins, and branched polysaccharides. Instead, for the fungal chitosan extraction, an enzymatic pre-treatment of the raw materials to hydrolyze the \(\beta\)-glucans or, alternatively, an optimized alkaline hydrolysis at low alkali concentrations were suggested. However, [PERSON] and colleagues [7] demonstrated that not all of the \(\beta\)-glucans composing the fungal cell wall are soluble in alkaline solution.