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

Abstract

Abstract Lactobacillus paracasei are found in many cheeses at high numbers and our objective was to study their potential contribution to the flavour development by amino acid catabolism. Aminotransferase (AT) activity was found in cell-free extracts of a Lactobacillus paracasei subsp. paracasei strain. An AT active fraction was prepared with specificity for degradation of the branched-chain amino acids leucine, isoleucine and valine, from which aroma compounds are derived that may contribute to cheese flavour. Sulphuric, charged or aromatic amino acids were not degraded. Response surface modelling with leucine and α -ketoglutaric acid ( α KGA) as amino group donor and acceptor, respectively, was used to study the kinetic of partly purified AT in the cell extract. K m for α KGA of partly purified AT was estimated to 0.5 m m . An inhibitor effect on glutamic acid production from α KGA was obtained at large α KGA concentration.