Crustacean and Mollusc Shell Proteins: Origin, Structure, and Functionality

matrix and structural complexity of the Bouligand-type structure of crab exoskeleton. However, mollusc shells are primarily mineralized structures composed of calcium carbonate (95%-99%), with a smaller organic fraction (1%-5%) consisting mainly of proteins, glycoproteins, and polysaccharides. Compared with crustacean shells, molluscan shells have lower protein content. This review critically evaluates the shell protein valorization and extensive data on composition and extraction strategies, such as green methods. The multifunctionality of shell-derived compounds also extends to pharmaceutical, biomedical, and environmental domains. Although research on shell valorization is expanding, critical gaps remain in techno-economic feasibility, allergenicity assessment, regulatory clarity, and the development of scalable processing techniques. Overcoming these barriers requires integrated efforts across food science, biotechnology, and sustainability practices. By integrating green extraction technologies, compositional profiling, and food system applications, this review advances innovative and sustainable pathways for crab shell valorization aligned with circular bioeconomy principles.