Analytical characterization of collagen-based dietary supplements: current approaches, analytical challenges and metrological perspectives

Hydrolyzed collagen-based dietary supplements received significant market expansion in recent years, increasing the demand for reliable analytical methodologies capable of ensuring product quality, authenticity, and regulatory compliance. However, the characterization of these products remains challenging due to the structural complexity of collagen-derived materials, variability associated with hydrolytic processes and raw material sources, and the presence of multiple components commonly found in commercial formulations. Different analytical techniques have been employed for amino acid profiling, hydroxyproline determination, and overall characterization of collagen-based materials, with chromatographic methods coupled to optical and mass spectrometric detection systems standing out due to their selectivity, sensitivity, and structural characterization capability. This review critically discusses the main analytical strategies applied to collagen analysis, including hydrolysis procedures, derivatization approaches, liquid chromatographic methods with optical detection, and LC-MS/MS-based methodologies, with emphasis on analytical validation and metrological aspects. Significant limitations associated with traditional nitrogen-based methods, hydroxyproline determination, amino acid profiling, matrix effects, and insufficient validation using real commercial supplement matrices are also discussed. A major gap identified in the literature is the lack of harmonized, metrologically traceable, and properly validated methodologies specifically designed for the analysis of complex commercial collagen supplements. Finally, future perspectives involving more robust metrological approaches are presented as complementary strategies for improving analytical reliability, traceability, and characterization of collagen-based dietary supplements.