Gas chromatography–mass spectrometry‐based quantitative method using tert‐butyldimethylsilyl derivatization for plasma levels of free amino acids and related metabolites in Japanese Black cattle

Abstract The quantification of amino acid and related metabolite levels is important for evaluating amino acid metabolism and function in animals. However, a useful quantitative method is not enough. In this study, we developed and validated tert ‐butyldimethylsilyl derivatization method using gas chromatography–mass spectrometry to quantify plasma levels of free amino acids and related metabolites in Japanese Black cattle. Of the 51 metabolites examined, 24, including 20 amino acids, one amine, and three keto acids, could be quantified. Compared with the trimethylsilyl derivatization method using gas chromatography–mass spectrometry, which has been used for untargeted metabolomic analysis, the present method had higher analytical reliability. This method is advantageous for assessing branched‐chain amino acid (BCAA) metabolism because it enables the quantification of not only BCAA levels (valine, leucine, and isoleucine) but also their bioactive metabolite keto acid levels (2‐ketoisovaleric acid, 2‐ketoisocaproic acid, and 2‐keto‐3‐methylvaleric acid) in the plasma. In addition, this method can quantify the plasma levels of not only tryptophan but also its bioactive metabolites kynurenine and serotonin. These results suggest that this quantitative method has the potential to further our understanding of amino acid metabolic processes and their functions in Japanese Black cattle.