Selenized Sodium Alginate: Characterization and Its Effects on Muscle Nutritional Quality and Flavor Profile under High-Carbohydrate Challenge in Micropterus salmoides

Abstract Sodium alginate was selenized via a BaCl2-catalyzed HNO3–Na2SeO3 method to produce selenized sodium alginate (Se-SA). Structural characterization confirmed covalent Se–O–C grafting, spherical nanoparticle formation (∼100 nm), and moderate depolymerization. A 12-week feeding trial with juvenile Micropterus salmoides (∼10 g) compared a high-carbohydrate diet (HC, 20%), HC + 1.0 mg/kg Na2SeO3 (HC-Se), HC + 1.0 mg/kg Se-SA (HC-Se-SA), and HC + 1.0 mg/kg sodium alginate (HC-SA). Dietary Se-SA significantly improved growth performance compared with other dietary treatments. Se-SA was associated with hepatic AMPKα activation and coordinate glycolipid gene regulation, correlating with reduced hepatic steatosis and improved glucose tolerance. Muscle n-3 PUFA content, texture, and antioxidant capacity were enhanced. HS-GC-IMS revealed remodeling of the volatile metabolome toward desirable aroma-active compounds and away from off-odors. These findings support Se-SA as a multifunctional polysaccharide additive for improving flesh quality in carbohydrate-intensive aquaculture.