Intramolecular Carbon Isotopic Composition of Monosodium Glutamate:  Biochemical Pathways and Product Source Identification

Monosodium glutamate (MSG) obtained as trade samples from several manufacturers was studied to determine the range of its intramolecular 13C/12C composition. Although the carbon isotopic composition of the total MSG molecule did not differ among manufacturers in most instances, significant differences were observed in the isotopic composition of the α-carboxyl carbon, suggesting that different proprietary strains of industrial microorganisms or MSG purification methods may impart unique isotopic fingerprints upon their products. The 13C depletion of the α-carboxyl carbon relative to the rest of the molecule helps constrain the identity of the potential anapleurotic carboxylating enzymes responsible for its fixation. Keywords: Monosodium glutamate; carbon isotopes; anapleurotic pathway; intramolecular isotope distribution