Flavour formation by lactic acid bacteria and biochemical flavour profiling of cheese products.
AIM Development of a fast, automated and reliable screening method for screening of large collections of bacterial strains with minimal handling time. METHODS AND RESULTS The method is based on the injection of a small headspace sample (100 microl) from culture vials (2 ml) in 96-well format directly into the mass spectrometry (MS). A special sample tray has been developed for liquid media, and anaerobically grown cultures. In principle, all volatile components can be measured, but a representative mass fragment has to be obtained in the MS. Representative masses for 3-methylbutanal, 2-methylpropanal and benzaldehyde are 58, 72 and 105, respectively. In 1 day over 1500 samples could be analysed and the coefficient of variation for the response was <5%. CONCLUSION Screening of 72 strains belonging to the genus Lactococcus in quadruple on the production of the key-flavour compound 3-methylbutanal illustrated the effectiveness of the method. Furthermore, knowledge of the biochemistry and physiology of 3-methylbutanal formation was used to optimize the composition of the growth medium to enhance 3-methylbutanal production, and thereby improve the screening. SIGNIFICANCE AND IMPACT OF THE STUDY A commonly used method to control flavour formation in fermented food products is the selection of bacterial strains, which are able to produce the desired flavour compounds. As large collections of strains are available for such screenings, studying biodiversity of micro-organisms on the level of metabolic routes is strongly facilitated by highly automated high throughput screening methods for measuring enzyme activities or production of metabolites. Therefore, this method will be a useful tool for selecting flavour-producing strains and for enhancing starter culture development.