Circular economy in seafood processing: turning crustacean by-products into astaxanthin bioresources.

As a naturally occurring oxygenated carotenoid, Astaxanthin (AST) is widely distributed in crustaceans. Its unique chemical structure endows it with multiple bioactivities including antioxidation, anti-inflammation and neuroprotection. The global crustacean processing industry generates a huge quantity of by-products such as heads, shells and viscera annually. These by-products have long been subjected to low-value utilization or direct discard, which not only causes resource waste but also triggers environmental problems, forming a huge potential resource pool urgently to be exploited. This review systematically establishes the intrinsic correlation between the molecular structure of AST and its bioactivities. It further elucidates the underlying molecular mechanisms responsible for its antioxidant, anti-inflammatory, and anti-metabolic syndrome effects, primarily through the regulation of key signaling pathways such as NF-κB and Nrf2. Additionally, this work critically summarizes recent advances in green and efficient extraction technologies, including enzymatic hydrolysis, supercritical CO₂ extraction, ultrasound-assisted extraction, and their integrated approaches, with a focus on the respective merits and limitations of each method. This review underscores the sustainable valorization of crustacean byproducts, emphasizing their transition from processing waste to high-value products through emerging applications in functional foods, cosmetics, and biomedicine. To address the critical challenges of poor stability and low bioavailability associated with AST, innovative nanodelivery strategies are highlighted as effective technological solutions., including nanoemulsions, targeted nanoparticles, and liposomes. Collectively, this work provides a comprehensive framework for advancing the resource utilization of crustacean-derived byproducts, accelerating the technological development of the AST industry, and supporting sustainable progress within the food and health sectors.