Direct determination of taste-active α, γ-glutamyl peptides in meat using LC-MS/MS with isotope-diluted assay

Abstract

γ-Glutamyl peptides rather than their α-isomers are a class of kokumi taste-active substances. The simultaneous determination of α- and γ-glutamyl peptides would be of great importance and could facilitate the flavor research in food science. Until now, LC/GC-MS method combined with chemical derivatization as well as CE-MS have been utilized to separate α- and γ- glutamyl peptides, but have shown the disadvantages of the inconvenience and the time-consuming. Here in this study, LC-MS/MS method with the isotope dilution assay was utilized to directly analyze α- and γ-glutamyl peptides in which γ-Glu-Cys-Gly(glutathione)-¹³C₂¹⁵N₁ was utilized as an internal standard. Taking six pairs of α- and γ-glutamyl peptides commonly existed in meat as the research models, the baseline separation and accurate quantitation could be achieved. The limits of quantitation (LOQs, S/N = 10) were in the range of 4–20 μg∙kg⁻¹. The average recoveries at the three spiking levels of 20, 100, 200 μg∙kg⁻¹, ranged from 75.50 % to 108.49 % in meat matrix, and the RSDs of peak area were ranged from 1.46 % to 13.03 %, showing good accuracy and precision. The method has been successfully applied in the determination of glutamyl peptides isomers in five meat samples, indicating the good performance and application prospects for the rapid screening of taste-active substances.