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-
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.