title: Synthesis and sensory characterization of novel umami-tasting glutamate glycoconjugates.
abstract: Two glycoconjugates of glutamic acid, namely, the N-glycoside dipotassium N-(d-glucos-1-yl)-l-glutamate (1) and the corresponding Amadori compound N-(1-deoxy-d-fructos-1-yl)-l-glutamic acid (2), have been synthesized in yields of 35 and 52%, respectively, using new Maillard-mimetic approaches, and their chemical structures have unequivocally been elucidated by 1D- and 2D-NMR and MS experiments. Systematic sensory studies revealed that both glycoconjugates exhibit pronounced umami-like taste with recognition taste thresholds of 1-2 mmol/L, close to that of monosodium glutamate (MSG). Contrary to an aqueous solution of MSG, 1 does not show the sweetish and slightly soapy by-note, but evokes an intense umami taste. Aqueous solutions of 2 were described by the descriptors umami, seasoning, and bouillon-like. Added to a bouillon base, which did not contain any taste enhancers, both glycoconjugates imparted a distinct umami character similar to the control sample containing the same amount of MSG on a molar basis. To the best of our knowledge, these types of glycoconjugates in general and, in particular, N-glucosyl glutamate and N-deoxyfructosyl glutamate have never been reported as taste active compounds having umami-like properties. Therefore, 1 and 2 represent a new class of umami-type taste compounds showing properties similar to the umami reference compound MSG. Systematic (13)C NMR measurements revealed that 1 was fairly stable in aqueous solutions under alkaline conditions (pH 8-10) as well as in dry form. However, it rapidly hydrolyzes in neutral and acidic solutions, giving rise to glucose and glutamate. In contrast, glycoconjugate 2 was observed to be rather stable in aqueous solution as well as in the presence of human saliva.
authors.affiliation: Deutsche Forschungsanstalt für Lebensmittelchemie, Lichtenbergstrasse 4, 85748 Garching, Germany.
authors.forename: Ersan
authors.initials: E
authors.lastname: Beksan
authors.forename: Peter
authors.initials: P
authors.lastname: Schieberle
authors.forename: Fabien
authors.initials: F
authors.lastname: Robert
authors.forename: Imre
authors.initials: I
authors.lastname: Blank
authors.forename: Laurent Bernard
authors.initials: LB
authors.lastname: Fay
authors.forename: Hedwig
authors.initials: H
authors.lastname: Schlichtherle-Cerny
authors.forename: Thomas
authors.initials: T
authors.lastname: Hofmann
mesh_terms: D005421:Flavoring Agents / Q000138:chemical synthesis*; D005632:Fructose / Q000031:analogs & derivatives / Q000138:chemical synthesis; D005960:Glucosides / Q000138:chemical synthesis; D018698:Glutamic Acid / Q000031:analogs & derivatives* / Q000138:chemical synthesis; D006001:Glycoconjugates / Q000138:chemical synthesis*; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D015416:Maillard Reaction; D015394:Molecular Structure; D012970:Sodium Glutamate; D012996:Solutions; D013649:Taste; D014867:Water
chemical_list: D005421:Flavoring Agents; D005960:Glucosides; D006001:Glycoconjugates; C477733:N-(1-deoxyfructos-1-yl)glutamic acid; C477732:N-(glucos-1-yl)glutamic acid; D012996:Solutions; D014867:Water; D005632:Fructose; D018698:Glutamic Acid; D012970:Sodium Glutamate