title: Detection and identification of the cross-linking amino acids N tau- and N pi-(2'-amino-2'-carboxy-ethyl)-L-histidine ("histidinoalanine", HAL) in heated milk products.
abstract: An unknown ninhydrin positive compound, X, was detected in acid hydrolysates of heated skim milk samples by amino acid analysis, eluting between phenylalanine and pyridosine in the chromatogram. The formation of X correlated with heating time and temperature. preparative ion-exchange chromatography enabled the isolation of X and a second minor compound from a milk protein hydrolysate and from a model mixture consisting of N alpha-acetylhistidine and methyl-2-acetamidoacrylate (acetyldehydroalaninemethylester), in a relative abundance of 8 to 1. By 1H-NMR spectroscopy, the two compounds could be identified as the N tau- and N pi-isomers of N-(2'-amino-2'-carboxy-ethyl)-L-histidine (histidinoalanine), a cross-link amino acid that has not been described in food proteins up to now. In a number of foods containing milk protein, the N tau-histidinoalanine contents were between 50 and 1800 mg/kg protein, which is in a concentration range comparable to the potential nephrotoxic cross-link lysinoalanine, which was determined simultaneously.
authors.affiliation: Lehrstuhl für Milchwissenschaft, Technische Universität München, Freising-Weihenstephan, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Henle
authors.forename: A W
authors.initials: AW
authors.lastname: Walter
authors.forename: H
authors.initials: H
authors.lastname: Klostermeyer
mesh_terms: D000818:Animals; D002852:Chromatography, Ion Exchange; D004151:Dipeptides / Q000032:analysis* / Q000302:isolation & purification; D006358:Hot Temperature; D008241:Lysinoalanine / Q000032:analysis; D009682:Magnetic Resonance Spectroscopy; D008892:Milk / Q000737:chemistry*
chemical_list: D004151:Dipeptides; C034124:histidinoalanine; D008241:Lysinoalanine