Crustacean Processing By-Products as Sustainable Sources of Bioactive Compounds: A Comprehensive Review of Conventional and Emerging Extraction Technologies and Applications

Crustacean processing industries, particularly those that process shrimp, crab, and lobster, generate substantial quantities of biological waste, consisting primarily of shells, heads, and exoskeletons. These by-products contribute significantly to environmental pollution due to their high organic load, slow degradability, and improper disposal practices. Nevertheless, they represent valuable reservoirs of bioactive compounds such as chitin, proteins, polyunsaturated fatty acids, carotenoids, and minerals, as well as biologically active enzymes and enzyme inhibitors, which possess immense potential in food, pharmaceutical/cosmetic, biomedical and environmental sectors. Unlike previous studies that primarily focus on individual components or specific extraction techniques, this review comparatively evaluates both conventional extraction techniques (acid–alkali treatment and solvent extraction) and emerging green approaches (supercritical fluid extraction, enzymatic hydrolysis, pulsed electric fields, ultrasound-assisted extraction, cold plasma, microwave-assisted extraction and high-pressure processing), highlighting their efficiencies, sustainability, and influence on compound quality. The review study further explores the diverse applications of the recovered constituents in food preservation, nutraceutical development, biodegradable packaging, and functional ingredient formulation. Moreover, current challenges concerning process optimization, industrial scalability, economic feasibility, and environmental impact are critically evaluated.