## 5 Biodegradability of Chitosan Derivatives and Life Cycle Assessment (LCA)  
Since the last decade, the biodegradability of CS has been extensively studied, notably to produce COS, which present varying bioactivities and numerous potential applications in food, agriculture, biomedicine, pharmaceutics, and cosmetics [217; 218]. The combination of chemical (e.g., acidic depolymerization) and physical processes constitute the well-known way of producing COS [18; 219; 220; 221], but these treatments nevertheless yield poorly defined oligosaccharidesable combinations varying in their DP, pattern of acetylation (PA), and fraction of acetylation (FA). Alternatively, CS depolymerization using enzymatic hydrolysis seems to be more relevant for COS production since it involves a more gentle and controlled procedure (pH, temperature), leading to a better control of Mw distribution of COS [221] and generation of more defined products [222; 223]. However, as the efficiency of enzymatic hydrolysis of CS remains dependent on PA and FA, the chemical states of CS used as a substrate may influence the composition of enzymatic products [224; 225]. CS has been reported to be susceptible to numerous enzymes, including specific (chitosanases, E.C. 3.2.1.132; chitinases, E.C. 3.2.1.14) and non-specific (glycosidase, lipase, proteases, etc.) CS hydrolyzing enzymes [226]. Non-specific chitosanolytic enzymes belong to heterogeneous enzyme families such as cellulase [227], amylase [228], pectinase [229], papain [230], lysozyme [231; 232], or lipases [233] (Table 4). Although chitinases and chitosanases are very effective, the utilization of non-specific enzymes is more suitable for the low-cost production of COS [234]. Among non-specific enzymes, cellulases showing bifunctional activities (cellulase-chitosanases) have been well-documented and were isolated from various organisms, such as _Bacillus_ sp., _Trichoderma_ sp., and _Lysobacter_ sp. [235; 236; 237; 238; 239]. With activities and reaction conditions varying according to the sources, some cellulase lead, by an endo-type cleavage, to final hydrolysis products distributed from dimers to tetramers [227]. Chitosanolytic activity associated with bifunctional cellulase may represent 15-40% of cellulase activity [236] and be enhanced with increasing deacetylation degree [240; 241]. Furthermore, chitosanases are generally recognized as enzymes degrading specifically CS, but not chitin, and have been classified into three subclasses according to the nature of the cleavage positions: GlcN-GlcNAc and GlcNAc for subclass I, GlcN-GlcNAc for subclass II, and GlcN-GlcNAc for subclass III [222]. These enzymes, belonging to five Glycos hydrolase families (GH-5, -8, -46, -75, and -80), degrade CS _via_ an endo-type mechanism. However, new enzymes with exochitosanase activity have been reported, notably exo-\(\beta\)-d-glucosamine able to cleave CS from non-reducing termini, releasing GlcN residues [242; 243]. Recently, the identification of a carbohydrate binding domain (CBM) for some chitosanases may suggest additional interaction with the CS polymer, involving a different mode of CS hydrolysis [244; 245]. The chitosanases described are issued from many organisms, including bacteria, cyanobacteria, fungi, and plants [222]. Although the performance of chitosanases on CS depolymerization is largely dependent on enzyme sources and reaction conditions, it has the advantage of being able to design a selected enzyme mixture to generate the controlled production of COS with selected DP or perform the complete CS hydrolysis to GlcN free [222; 239]. On the other hand, the biodegradation of CS derivatives relative to chemically modified or grafted-CS copolymers was also investigated using enzymatic hydrolysis, e.g. C6-oxidized CS [133], CS phenolic [251], CS/hyaluronan [231], or CS/alginate [252]. As an example, a commercialized enzymes mixture (Glucanex(r), Macerozyme R-10) and crude extract from _T.