DNA Barcoding and Comparative Nutritional Profiling of "Cod" () Products from Chinese E-Commerce Platforms

The commercial designation "cod" () is applied to multiple fish species, raising concerns regarding seafood authenticity and nutritional consistency. This study combined DNA barcoding with comparative nutritional profiling to authenticate frozen products marketed as "cod" () from major Chinese e-commerce platforms and to evaluate nutritional differences among the identified species. Among the 36 products analyzed, eight fish species were identified: three Gadiformes species (55.6%) and five non-Gadiformes species (44.4%). Interspecific differences were observed in proximate composition, amino acid composition, free amino acid profiles, and fatty acid composition. True cod species exhibited higher protein contents (>19.0%), lower lipid contents (0.51-1.02%), and higher proportions of EPA + DHA (35.61-37.10% of total fatty acids) than non-Gadiformes species. In contrast, non-Gadiformes species generally contained higher lipid levels (15.02-23.09%), lower proportions of long-chain ω-3 PUFA, and distinct flavor-related amino acid profiles. Lepidocybium flavobrunneum showed the lowest EPA + DHA proportion (5.81%) and the highest concentration of bitter-tasting free amino acids (0.661 g/100 g). These findings reveal substantial nutritional heterogeneity among the authenticated species marketed as "cod" (), demonstrating that DNA barcoding provides an essential foundation for linking species identity to nutritional quality assessment.