Development of cheese flavour from peptides and amino acids by cell-free extracts of Lactococcus lactis subsp cremoris B78 in a model system

The formation of a cheese-like flavour from amino acids and peptides, by the action of enzymes from Lactococcus lactis subsp. cremoris B78, a Gouda cheese starter organism, was investigated. Cell-free extract (CFE) was obtained from the organism after ultrasonic disruption of cells and subsequent removal of cell debris by centrifugation. The CFE was ultrafiltered to remove low-molecular-mass compounds (<500 Da). The retentate (CFE>500) was used as an enzyme source in incubation experiments with various mixtures of amino acids in water and with peptide solutions. These peptide solutions contained the alpha(sl)-casein peptides alpha(sl)-CN(f1-23) and alpha(sl)-CN(f24-199) or a mixture of peptides of molecular weight 500-5000 Da, isolated from Gouda cheese. The solutions were incubated aseptically for one week at 25 degrees C. Sensory analysis showed that a cheese-like flavour developed in amino acid mixtures containing free methionine or in mixtures of peptides containing methionine. In the latter case, methionine was released from the peptides by the action of proteolytic enzymes in the CFE>500. The formation of volatile sulphur compounds from methionine could be demonstrated by gas chromatography-mass spectrometry. The results indicated that non-proteolytic enzymes from mesophilic lactococci are important for flavour formation in cheese.