The nature of aroma compounds produced in a cheese model by glutamate dehydrogenase positive Lactobacillus INF15D depends on its relative aminotransferase activities towards the different amino acids

Recently, we demonstrated that mesophilic lactobacilli exhibiting glutamate dehydrogenase (GDH) activity were capable of degrading aromatic amino acids (ArAAs) and branched-chain amino acids (BcAAs) in vitro to precursors of aroma compounds and to aroma compounds, when they were combined with Lactococcus lactis. Indeed, they produced via their GDH activity the aketoglutarate required for the amino acid transamination. In the present study, we compared the ability of two Lactobacillus strains, with and without GDH activity, to produce aroma compounds from amino acids in a cheese model. The GDH-positive Lactobacillus INF15D produced mainly diacetyl and acetoin from catabolism of aspartate (Asp). However, there were no aroma compounds produced from BcAAs, even when Lactobacillus was combined with L. lactis. In fact, Lactobacillus INF15D exhibited 5-10-fold higher aminotransferase (AT) activity towards Asp than towards BcAAs. We concluded that due to competition of ATs for the a-ketoglutarate produced by GDH, the aroma compounds produced in cheese depends on the relative AT activities towards Asp, BcAAs and ArAAs of the GDH-positive strain. (C) 2003 Elsevier Ltd. All rights reserved.