Transamination of branched-chain amino acids by a cheese related Lactobacillus paracasei strain

Lactobacillus paracasei are found in many cheeses at high numbers and our o bjective was to study their potential contribution to the flavour developme nt by amino acid catabolism. Aminotransferase (AT) activity was found in ce ll-free extracts of a Lactobacillus paracasei subsp. paracasei strain. An A T active fraction was prepared with specificity for degradation of the bran ched-chain amino acids leucine, isoleucine and valine, from which aroma com pounds are derived that may contribute to cheese flavour. Sulphuric, charge d or aromatic amino acids were not degraded. Response surface modelling wit h leucine and alpha -ketoglutaric acid (alpha KGA) as amino group donor and acceptor, respectively, was used to study the kinetic of partly purified A T in the cell extract, K-m for alpha KGA of partly purified AT was estimate d to 0.5 mm. An inhibitor effect on glutamic acid production from alpha KGA was obtained at large alpha KGA concentration. (C) 2001 Elsevier Science L td. All rights reserved.