ORIGINAL ARTICLE Determination and stereochemistry of proteinogenic and non-proteinogenic amino acids in Saudi Arabian date fruits Hatem Salama Mohamed Ali • Omar Amin Alhaj • Abdulrahman Saleh Al-Khalifa • Hans Bru ¨ ckner Received: 21 May 2014 / Accepted: 23 May 2014 / Published online: 18 June 2014 Ó Springer-Verlag Wien 2014 Abstract Whereas an abundance of literature is available on the occurrence of common proteinogenic amino acids (AAs) in edible fruits of the date palm (Phoenix dactylifera L.), recent reports on non-proteinogenic (non-coded) AAs and amino components are scarce. With emphasis on these components we have analyzed total hydrolysates of twelve cultivars of date fruits using automated ion-exchange chro- matography, HPLC employing a fluorescent aminoquinolyl label, and GC–MS of total hydrolysates using the chiral sta- tionary phases Chirasil Ò -L-Val and Lipodex Ò E. Besides common proteinogenic AAs, relatively large amounts of the following non-proteinogenic amino acids were detected: (2S,5R)-5-hydroxypipecolic acid (1.4–4.0 g/kg dry matter, DM), 1-aminocyclopropane-1-carboxylic acid (1.3–2.6 g/kg DM), c-amino-n-butyric acid (0.5–1.2 g/kg DM), (2S,4R)-4- hydroxyproline (130–230 mg/kg DM), L-pipecolic acid (40–140 mg/kg DM), and 2-aminoethanol (40–160 mg/ kg DM) as well as low or trace amounts ( \ 70 mg/kg DM) of L-ornithine, 5-hydroxylysine, b-alanine, and in some samples ( \ 20 mg/kg DM) of (S)-b-aminoisobutyric acid and ( \ 10 mg/kg DM) L-allo-isoleucine. In one date fruit, traces of a-aminoadipic acid could be determined. Enantiomeric analysis of 6 M DCl/D 2 O hydrolysates of AAs using chiral capillary gas chromatography–mass spectrometry revealed the presence of very low amounts of D-Ala, D-Asp, D-Glu, D- Ser and D-Phe (1.2–0.4 %, relative to the corresponding L- enantiomers), besides traces (0.2–1 %) of other D-AAs. The possible relevance of non-proteinogenic amino acids in date fruits is briefly addressed. Keywords Phoenix dactylifera Á (2S,5R)-5- hydroxypipecolic acid Á 1-aminocyclopropane-1-carboxylic acid Á Non-coded amino acids Á D-amino acids Á Plant amino acids Á Ion-exchange chromatography Á GC–MS Á Nutritional relevance Abbreviations GC–MS Gas chromatography mass spectrometry M Molecular mass (weight) HPLC or LC High performance liquid chromatography SIM Selected ion monitoring AQC 6-Aminoquinoyl-carbamyl-N- hydroxysuccinimidyl carbamate AMQ 6-Aminoquinoline iTRAQ TM Isobaric tag for relative and absolute quantitation MSTFA N-methyl-N-trimethylsilyl- trifluoroacetamide DCl/D 2 O Deuterium chloride in deuterium oxide TFAA Trifluoroacetic acid anhydride TFA Trifluoroacetyl Me Methyl Et Ethyl Presented in part as lecture (by HSMA) at the Fifth International Date Palm Conference, 16–18 March 2014, Abu Dhabi, United Arab Emirates. H. S. M. Ali Á O. A. Alhaj Á A. S. Al-Khalifa Department of Food Science and Nutrition, College of Food Science and Agriculture, King Saud University, P.O. Box 2460, Riyadh 11451, Kingdom of Saudi Arabia H. Bru ¨ckner (&) Department of Food Sciences, Research Center for BioSystems Land Use and Nutrition (IFZ), Institute of Nutritional Science, Justus-Liebig-University of Giessen, Heinrich-Buff-Ring 26-32, 35392 Giessen, Germany e-mail: hans.brueckner@ernaehrung.uni-giessen.de H. Bru ¨ckner King Saud University, Riyadh, Kingdom of Saudi Arabia 123 Amino Acids (2014) 46:2241–2257 DOI 10.1007/s00726-014-1770-7