title: Use of non-growing Lactococcus lactis cell suspensions for production of volatile metabolites with direct relevance for flavour formation during dairy fermentations.
abstract: BACKGROUND
  Lactococcus lactis is a lactic acid bacterium that has been used for centuries in the production of a variety of cheeses, as these bacteria rapidly acidify milk and greatly contribute to the flavour of the fermentation end-products. After a short growth phase during cheese ripening L. lactis enters an extended non-growing state whilst still strongly contributing to amino acid-derived flavour formation. Here, a research approach is presented that allows investigation of strain- and amino acid-specific flavour formation during the non-growing state.
  
  
  RESULTS
  Non-growing cells of five selected L. lactis strains were demonstrated to degrade amino acids into flavour compounds that are relevant in food fermentations and differs greatly from production of flavour compounds using growing cells. As observed earlier in other research set-ups and with other microorganisms, addition of NADH, α-ketoglutarate and pyridoxal-5-phosphate was demonstrated to be essential for optimal flavour formation, suggesting that intracellular pools of these substrates are too low for the significant production of the flavour compounds. Production of flavours during the non-growing phase strongly depends on the individual amino acids that were supplied, on the presence of other amino acids (mixtures versus single compounds), and on the strain used. Moreover, we observed that the plasmid-free model strains L. lactis MG1363 and IL1403 produce relatively low amounts of flavour components under the various conditions tested.
  
  
  CONCLUSIONS
  By using this simplified and rapid approach to study flavour formation by non-growing lactic acid bacteria, lengthy ripening periods are no longer required to assess the capacity of strains to produce flavours in the long, non-growing state of dairy fermentation. In addition, this method also provides insight into the conversion of single amino acids versus the conversion of a mixture of amino acids as produced during protein degradation. The generated results are complementary to earlier generated datasets using growing cells, allowing assessment of the full flavour forming potential of strains used as starter cultures in industrial food fermentation processes.
authors.affiliation: TI Food and Nutrition, Wageningen, The Netherlands. bertvandebunt@solcon.nl.|NIZO food research, Ede, The Netherlands. bertvandebunt@solcon.nl.
authors.forename: Bert
authors.initials: B
authors.lastname: van de Bunt
authors.affiliation: TI Food and Nutrition, Wageningen, The Netherlands. peter.bron@nizo.com.|NIZO food research, Ede, The Netherlands. peter.bron@nizo.com.|The Kluyver Centre for Genomics of Industrial Fermentations/NCSB, Delft, The Netherlands. peter.bron@nizo.com.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Bron
authors.affiliation: TI Food and Nutrition, Wageningen, The Netherlands. lolke.sijtsma@tifn.nl.|The Kluyver Centre for Genomics of Industrial Fermentations/NCSB, Delft, The Netherlands. lolke.sijtsma@tifn.nl.|Wageningen UR Food & Biobased Research, Wageningen, The Netherlands. lolke.sijtsma@tifn.nl.
authors.forename: Lolke
authors.initials: L
authors.lastname: Sijtsma
authors.affiliation: Laboratory of Microbiology, Wageningen University, Wageningen, The Netherlands. willem.devos@wur.nl.|Department Veterinary Biosciences, University of Helsinki, Helsinki, Finland. willem.devos@wur.nl.
authors.forename: Willem M
authors.initials: WM
authors.lastname: de Vos
authors.affiliation: University of Amsterdam, Swammerdam Institute of Life Sciences, Science park 904, PO Box 94216, 1090, GE, Amsterdam, The Netherlands. Jeroen.hugenholtz@corbion.com.
authors.forename: Jeroen
authors.initials: J
authors.lastname: Hugenholtz
mesh_terms: D000818:Animals; D002611:Cheese / Q000382:microbiology; D013294:Lactococcus lactis / Q000378:metabolism*; D055549:Volatile Organic Compounds / Q000378:metabolism*
chemical_list: D055549:Volatile Organic Compounds