An insight into kinetics and thermodynamics of gamma-aminobutyric acid production by Enterococcus faecium CFR 3003 in batch fermentation

In the present study, a kinetic and thermodynamic model for production of gamma-aminobutyric acid (GABA) using Enterococcus faecium CFR 3003 is proposed. Differential production of GABA in complex-minimal media indicated that the minimal medium (Modified TYG: Tryptone, Yeast extract and Glucose) supported the highest production of GABA. The influence of variables such as monosodium glutamate (MSG) concentration (1-5 %), temperature (25-60 A degrees C) and pH (4.0-8.0) on GABA production was studied. The kinetics on the rate of MSG consumption (rs) as a function of MSG concentration [S] was studied by assuming Monod's model for the MSG-uninhibited region and Briggs-Haldane model for the MSG-inhibited domain. The experimental kinetic parameters determined were found to be in good agreement with the predicted ones. Arrhenius model was used to calculate the thermodynamic parameters. The activation energy for the growth, activation enthalpy and entropy for GABA formation were found to be 80.13, 87.29 and 0.273 kJ mol(-1) K-1, respectively. A process product yield (Y-P/S) of 0.64 g GABA g(-1) MSG could be reached with a volumetric rate of GABA formation, Q(P) (0.159 g l(-1) h(-1)) and MSG consumption Q(S) (0.145 g l(-1) h(-1)), respectively, under optimized conditions. This contributed to a GABA concentration of 8 g l(-1) at the end of 48 h of fermentation time, which is 2.9-fold higher than that under unoptimized conditions.