A hydrophilic interaction chromatography-tandem mass spectrometry method for amino acid profiling in mussels

A UHPLC-HILIC-tandem MS method has been developed and validated for the quantification of 21 amino acids (20 protein amino acids and cystine) in their free form (FAA) and as protein constituents (total amino acids, TAA) in a rich protein food matrix such as lyophilized mussels (Mytilus galloprovincialis) samples. FAA were analyzed after suspending the samples in the presence of trichloroacetic acid in order to prevent dissolving the proteins, while TAA were determined after acid hydrolysis with 6M HCl in the presence of 4% v/v thioglycolic acid as a reducing agent. In hydrolysed samples 17 amino acids could be determined since tryptophan, cysteine, cystine and asparagine were degraded during acid hydrolysis. Linear regression coefficients (R²) were above 0.99 for all amino acids. Accuracy and precision, expressed as recovery (%) and relative standard deviation (RSD, %) were in acceptable levels, ranging from 78.2 to 123.3% and below 15%, respectively for both FAA and TAA. Uncertainty was also below 12% for FAA and below 22% for TAA. Sensitivity of the method was high with LOD values ranging from 0.003 to 0.034g/100g for FAA and 0.001 to 0.004g/100g for TAA, while LOQ ranged from 0.009 to 0.104g/100g for FAA and 0.002 to 0.011g/100g for TAA. The method proved to be a fast and reliable tool for acquiring information on free and total amino acids profile in high protein content foodstuffs such as mussels.