title: Conversion of amino acids into aroma compounds by cell-free extracts of Lactobacillus helveticus.
abstract: OBJECTIVE
  Lactobacillus helveticus is an essential starter in Swiss-type cheeses such as Emmental. This study was to determine whether cell-free extracts of Lact. helveticus were able to convert free amino acids into neutral volatile aroma compounds at the pH and temperature occurring in cheese.
  
  
  RESULTS
  A mix of branched-chain (Leu, Ile, Val), aromatic (Tyr, Phe) and sulphur (Met) amino acids was incubated for 7 days, at pH 5.7 and 24 degrees C, with cell-free extracts of six strains. The amino acids were all transaminated into the corresponding keto acids when an amino group acceptor (alpha-ketoglutaric acid) was provided. Phe and Tyr were transaminated the most efficiently, followed by Leu, Met, Ile and Val. Three major volatile compounds were detected by GC-MS: benzaldehyde, dimethyl disulphide and 2-methyl propanol. Whatever the strain, benzaldehyde was produced in the highest quantity (0.25-1 micromol l(-1) mg(-1) protein).
  
  
  CONCLUSIONS
  Lactobacillus helveticus intracellular enzymes could significantly contribute to the production of aroma compounds from amino acid catabolism.
authors.affiliation: DSM--Food Specialities B.V., Delft, The Netherlands.
authors.forename: N
authors.initials: N
authors.lastname: Klein
authors.forename: M B
authors.initials: MB
authors.lastname: Maillard
authors.forename: A
authors.initials: A
authors.lastname: Thierry
authors.forename: S
authors.initials: S
authors.lastname: Lortal
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D002611:Cheese / Q000382:microbiology*; D002851:Chromatography, High Pressure Liquid; D005421:Flavoring Agents / Q000378:metabolism; D005516:Food Microbiology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007778:Lactobacillus / Q000201:enzymology* / Q000254:growth & development; D009812:Odorants; D012903:Smell; D013696:Temperature; D000637:Transaminases / Q000302:isolation & purification / Q000378:metabolism*; D014835:Volatilization
chemical_list: D000596:Amino Acids; D005421:Flavoring Agents; D000637:Transaminases