Determination of underivatized amino acid dC by liquid chromatography/isotope ratio mass spectrometry for nutritional studies: the effect of dietary non-essential amino acid profile on the isotopic signature of individual amino acids in fish

*Correspo tems and Universit gart, Ger E-mail: fo yPresent Untere Se Contract/ GA 1068/ This study provides data for the effect of dietary non-essential amino acid composition on the dC values of individual amino acids in rainbow trout (Oncorhynchus mykiss) using liquid chromatography coupled to isotope ratio mass spectrometry (LC/IRMS). In this experiment, trout were reared either on a control diet or on three experimental diets, differing in the composition of non-essential/conditionally essential amino acids, for a period of 6 weeks. The control diet was a commercial trout starter feed with fish meal as the main protein source. The experimental diets contained no protein, only synthetic amino acids. Diet 1 resembled the composition of fish meal in both essential and non-essential amino acids, Diet 2 had all essential amino acids, but cysteine, glycine, proline and tyrosine were replaced by the corresponding amounts of their precursors, and in Diet 3 all non-essential amino acids were replaced by glutamate. LC/IRMS was used for the determination of dC values of individual amino acids from diets and tissues without derivatization. Diet affected the dC of individual amino acids in fish. For fish on Diets 1–3 amino acid dC values showed a similar trend: phenylalanine showed very little change from diet to body tissue. Arginine, lysine, tyrosine and proline showed strong depletion from diet to body tissue and glycine, alanine, aspartate and serine all showed variable but strong enrichment in C. Improvements are necessary before all amino acid dC values can be determined; however, this study demonstrates that measuring amino acid isotopic signatures by LC/IRMS is a promising new technique for nutritional physiologists. Copyright # 2008 John Wiley & Sons, Ltd.