*2.3.2.3 Chitin and chitosan*

Chitin is a biopolymer found in abundance in nature after cellulose [66]. It is found in cell wall of fungi, exoskeleton of crustaceans and many other biological materials [67]. Chitin contains poly (β-(1–4)-2-acetamido-d-glucose), and chitosan is obtained in the presence of alkalin from N-deacetylation [68]. Chitosan has anti-microbial property, which is very effective over yeast and mould, followed by Gram-positive and Gram-negative bacteria [15]. In mechanism of chitosan's antimicrobial action, it results in harmful leakage of microbial proteinaceouse and intercellular components when positive charge chitosan and negative charge microbial cell membrane are interacted. Chitosan helps to prevent toxic production and microbial growth in product because it contains nearly amount of chelate trace metals [69]. From shrimp shells, chitin is obtained about 30%. In the process of obtaining chitin, shells are treated with NaoH at 85–110°C, and after obtaining it, for removing the CaCO3, weak HCl solution was used at room temperature having about 1–10% concentration [70]. The physicochemical properties of Chitosan is dependent on the method used to obtained chitosan and used apparatuses [56]. It has been extensively used in films and coatings due to its ability to inhibit bacterial and fungal pathogens' growth [71]. Santos et al. [72] stated that the antimicrobial property of chitosan film is enhanced by the availability of fatty acids in it. Chitosan forms coating which is semi-permeable in nature, which helps in delaying the ripening rate of fruits and vegetables by modifying the internal atmosphere. For obtaining tough, flexible and clear film, chitosan is made from aqueous solution [73, 74].
