Advanced technologies for chitin recovery from crustacean waste

Chitin is the second most plentiful natural biomass after cellulose, with a yearly production of about 1 × 10 10 –1 × 10 12 tonnes. It can be obtained mainly from sea crustaceans' shells, containing 15–40% chitin. Full or partial deacetylation of chitin generates chitosan. Chitin and chitosan are used in several industrial sectors, as they exhibit high biocompatibility, biodegradability and several biological functions (e.g., antioxidant, antimicrobial and antitumoral activities). These biopolymers' market trends are destined to grow in the coming years, confirming their relevance. As a result, low-cost and industrial-scale production is the main challenge. Scientific literature reports two major technologies for chitin and chitosan recovery from crustacean waste: chemical and biological methods. The chemical treatment can be performed using conventional solvents, typically strong acid and alkaline solutions, or alternative green solvents, such as deep eutectic solvents (DESs) and natural deep eutectic solvents (NADESs). Biological methods use enzymatic or fermentation processes. For each route, this paper reviews the advantages and drawbacks in terms of environmental and economic sustainability. The conventional chemical method is still the most used but results in high environmental impacts. Green chemical methods by DESs and NADESs use low-toxic and biodegradable solvents but require high temperatures and long reaction times. Biological methods are eco-friendly but have limitations in the upscaling process, and are affected by high costs and long reaction times. This review focuses on the methodologies available to isolate chitin from crustaceans, providing a comprehensive overview. At the same time, it examines the chemical, biological and functional properties of chitin and its derivative, along with their most common applications. Consequently, this work represents a valuable knowledge tool for selecting and developing the most suitable and effective technologies to produce chitin and its derivatives.