The influence of environmental parameters on the catabolism of branched-chain amino acids by Staphylococcus xylosus and Staphylococcus carnosus

Degradation of the amino acids leucine, isoleucine and valine into branched flavour compounds by Staphylococcus xylosus and Staphylococcus carnosus was studied using resting cell cultures added to a defined reaction medium under different environmental conditions relevant to sausage fermentation. The environmental conditions studied were temperature (12-28degreesC), NaCl concentration (4.0-12.0% (w/w)) acidity (pH 4.8-5.8) and addition of manganese (0-2.5mg Mn/kg). Flavour compounds were sampled by automatic static headspace collection and separated/quantified using gas chromatography/flame ionization detection (GC/FID). Main volatile catabolic products of leucine, isoleucine and valine were 3-methylbutanoic, 2-methylbutanoic and 2-methylpropanoic acids, respectively. The generation of branched flavour compounds was influenced significantly by most of the investigated environmental parameters, but in particularly by temperature and NaCl. Raising the temperature increased the production of branched-chain acids by both S. xylosus and S. carnosus, whereas increasing NaCl concentration had a clear negative effect, reducing the concentrations of branched-chain acids for both species but in particularly for S. carnosus. The acidity of the medium was also important for both Staphylococcus spp., but with opposite effects. Lowering pH decreased the generation of branched-chain acids by S. carnosus but increased the generation by S. xylosus. In addition, several two-factor interactions between temperature, NaCl concentration and pH were significant. Manganese addition increased the branched-chain acid concentration slightly for S. xylosus but not for S. carnosus. (C) 2003 Elsevier Ltd. All rights reserved.