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Flavour formation from catabolism of amino acids

Acceleration and diversification of flavour formation in
semi-hard cheeses, by controlling amino-acid catabolism
with lactic acid bacteria (lab).

Accelerating or diversifying flavour development in cheese is of major economic interest since the final flavour of cheeses partly determines consumer choice and flavour development is a time-consuming and expensive process that is still not well mastered. Flavour development in cheese is a complex degradation process requiring the concerted action of proteolytic, lipolytic, glycolytic and amino- acid-converting enzymes (AACEs). An important initial step in flavour development is the proteolysis of milk caseins by the activity of rennet, and proteases and peptidases from starter culture lactic acid bacteria (LAB). The resulting peptides and free amino acids are then converted into flavour compounds through the action of AACEs. The proteolytic degradation process of milk caseins has been extensively studied, whereas the subsequent biochemical pathways from amino acids to flavour compounds have only been partially characterized. Previous studies, especially those carried out in the EUROPEAN COMMISSION's FAIR project CT97-3173, have demonstrated the major role of amino acid catabolism in the flavour formation in cheese and the possibilities of intensifying and diversifying flavour formation in cheese by controlling amino acid catabolism by lactic acid bacteria. These results open new avenues to intensify or diversify aroma formation in cheeses and especially in cheeses made from pasteurised milk without surface flora and also in low-fat cheeses. For such cheeses, flavour formation requires a very long ripening time (e.g. up to one year for cheddar). The aim of this project is to improve the flavour of this type of cheese (or accelerate flavour formation) and create new cheese varieties with new flavours, using selected and controlled internal flora. To do this, it is necessary to find criteria allowing strains with high or specific potential to be selected for flavour formation. These selected strains should also have the technological qualities required to become industrial ferments, which permit automation, reproducibility and safety in cheese- making. The first objective of the project is to establish a relationship between certain amino acid catabolic activities and high or specific potentials of aroma formation, in order to develop a screening method for the selection of strains with interesting aromatic properties. The basic research will use Lactococcus lactis which is widely used as starter in the cheese industry and constitutes the major flora of semi-hard cheeses. The project will be divided into 6 tasks. The first three are precompetitive research tasks while the remaining three are development tasks: 1. Identification of key amino acid converting enzymes (AACEs) for the formation of different aroma compounds. AACEs that prevent or slow down flavour formation will also be identified. The importance of key AACEs will be investigated by constructing deletion mutants or mutants that overexpress the enzyme. 2. Development of screening methods for key enzymes. Enzyme activity tests and molecular probes for corresponding genes will be developed. 3. Investigation of the possibilities of controlling key enzyme activities at the level of culture conditions. 4. Selection and/or construction by self-cloning of lactic acid bacteria (LAB) strains with desired activities. 5. Development of starters or adjunct cultures from selected or modified strains. 6. Cheese trials at small or pilot scale with selected or modified strains, new starters or new adjuncts. Keywords: flavour, cheese, lactic acid bacteria.
Project ID: 
2 536
Start date: 
11-12-2000
Project Duration: 
52months
Project costs: 
3 200 000.00€
Technological Area: 
Enzymology / Protein Engineering / Fermentation
Market Area: 
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