Skip to main content

Amélioration de la qualité et de la sécurité des fromages fabriqués à partirde lait cru

Objective

To reduce the level of contaminants at the very origin (from the animal, in slurry) and study the actual sources of contamination of the milk itself on the farm in order to eliminate them;

To develop new technology to improve the safety of raw milk while maintaining its quality for cheese manufacture. This implies studying the possibility of decontaminating the milk by means of physical techniques (microfiltration, centrifugation);

To make use of the potential of lactic starter microorganisms and also of the fungi, yeast or bacteria produced during the maturing process to inhibit harmful flora (in particular, the pathogenic Listeria monocytogenes).
A large number of European cheeses are still made from raw milk in order to obtain the characteristic taste desired by consumers. In view of the potential risks associated with the use of raw milk, research has been carried out in order to develop a full system of protection against the bacteria which endanger consumers.

The level of contamination by Listeria monocytogenes on farms has been found to be low. Hygiene during milking and in particular when cleaning the cows' teats is essential to guarantee that the milk is free from Listeria monocytogenes.
The origin of the large number of contaminant bacteria found on the surface of teats has not yet been established. Determination of the strains of Listeria found is still in progress and may provide further information and possibly confirm the theory regarding their origin.

Of several thousand bacteria tested,only a few strains of Lactococcus, Pediococcus and Enterococcus have been found to inhibit Listeria. In some of thse strains, it was found that this activity was due to the production of bacteriocins.
There is no reduction in antimicrobial activity following neutralization of the medium or the additon of catalase. These substances are thus inhibited or destroyed under the effects of certain proteolytic enzymes.

The effects of the culture medium on the quantity of bacteriocin produced have been studied. Purification of Pediococcus and Enterococcus bacteriocins is in progress.

The effects of the technological production parametes on the kinetics of the development of Escherichia coli and Staphylococcus aureus in Camembert have been studied. A statistical study of the results is in progress but long prematuring in the presence of bacteria has been found to have positive effects on slowing down the development of contaminating flora.

Finally, the internal and external flora of Camembert cheese has been characterized.
Problems of hygiene and quality of che
eses are a constant preoccupation of t
he entire dairy industry. In order to
insure consumer safety, the milk under
goes various heat treatments in order
to eliminate any potentially pathogeni
c flora. The obvious result of these t
reatments is to concomitantly destroy
the microbial flora which participate
in the process of cheese manufacture:
lactic acid bacteria, yeasts and bacte
ria responsible for ripening. In addit
ion, pasteurising destroys various enz
yme systems (oxido-reduction enzymes)
which may participate in the productio
n of final characteristic flavors.
There is thus a degradation of the org
anoleptic qualities of products manufa
ctured from pasteurised milk. In addit
ion, a non-negligible proportion of gu
aranteed origin cheeses is always manu
factured from raw milk in order to obt
ain the taste highly appreciated by co
nsumers. Furthermore, these technologi
es also lead to added profit from milk
in regions where agriculture is diffi
cult, notably mountainous regions, and
the dry Mediterranean zone; sheep mil
k may also be concerned by this. The s
ocio-economic impact is thus very impo
rtant for southern Europe and France.
In light of the potential dangers asso
ciated with the use of raw milk, it is
indispensable to develop an entire sy
stem of defense against bacteria which
pose a risk for man. This will insure
that the safety of these products, re
sponding to high consumer demand and a
lso benefiting agriculture in difficul
t regions, will be as great as that of
products manufactured with pasteurise
d milk and which will preserve their o
rganoleptic qualities.
The project includes several main axes
: 1. The reduction in the level of con
taminants at the level of the animals
and the study of sources of contaminat
ion, in order to be able to eliminate
them.
2. The development of new technologies
to improve the quality and safety of
raw milk used in cheese manufacture.
Possibilities of decontamination by ce
ntrifugation, creaming or microfiltrat
ion will be studied in particular.
3. Microbial antagonisms will be sough
t by the selection of lactic acid bact
eria producing factors which inhibit u
ndesirable, even pathogenic, organisms
. Special attention will be paid to th
e production of bacteriocins and/or ni
sin. A crucial point of the research w
ill be the effect of technological par
ameters on the behavior of new lactic
acid bacteria starters which will be s
elected and their effect on the elimin
ation of undesirable flora.
All this research will be applied to d
ifferent Camembert, Fontina, Asiago an
d Manchego type cheeses.

Coordinator

Besnier SA
Address
10 Rue Adolphe Beck
53000 Laval
France

Participants (4)

INSTITUT NATIONAL DE LA RECHERCHE AGRONOMIQUE
France
Address
Domaine De Vilvert
78352 Jouy-en-josas
Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria
Spain
Address

28080 Madrid
Istituto Sperimentale Lattiero-Caseario
Italy
Address
Via A. Lombardo 11
20075 Lodi Milano
Rijkszuivelstation
Belgium
Address
370,Brusselsesteenweg
9090 Melle