Extraction, identification and quantitation of carotenoids in discolored channel catfish (Ictalurus punctatus) fillets

Yellow discoloration of channel catfish fillets is a major quality concern to the catfish industry. This discoloration is thought to be caused mainly by dietary carotenoids, which are deposited as yellow regions within the fillet. In the present work, yellowish fillets were extracted and quantitatively analyzed for their carotenoid contents using an improved extraction procedure. The pigments found in discolored fillets were lutein, zeaxanthin, alloxanthin, and diatoxanthin. The identification of carotenoids was confirmed based on their accurate mass measurement, high-performance liquid chromatography (HPLC) retention time, and UV–vis spectrum. The carotenoid content in catfish fillets ranged from 58 ng/g for slightly yellow fillets to approximately 215 ng/g for the enhanced yellow fillets. Alloxanthin was identified as a principle carotenoid in channel catfish for the first time.