Starter Cultures for Meat Fermentation 2052005 ), thus increasing the competitiveness of
L. sakei in a meat environment.
The competiveness during fermentation is
strictly related to the ability of the cells to
adapt to the environmental conditions of the
meat batter and to the ecological conditions
present during fermentation. In a study on L.
sakei gene expression, environmental condi-
tions of sausage were found to induce 15
genes (H ü fner et al. 2007 ). Consistent with
the expected metabolic adaptation, these
genes code for proteins involved in the amino
acids and carbohydrate transport, lipid
metabolism, and stress response. The inacti-
vation of the heat shock regulator gene ctsR
resulted in an improved growth of L. sakei in
fermented sausages.
The ability of CNS to colonize cured and
fermented meats has been well described
(Leroy et al. 2006 ). Thus, these organisms,
which are present in the adventitious micro-
biota of meat or are added as starter cultures
to the batter, become a dominant population
during fermentation. Physiological proper-
ties, such as the ability to grow at low tem-
peratures and low water activity, contribute
to the competiveness. Information derived
from the S. carnous genome provides a sci-
entifi c basis for adaptation to low water
activity environments, such as cured and fer-
mented meat. Nine pathways involved in
osmoprotection, which contribute to the
accumulation of biocompatible solutes in the
cytoplasm, are present in S. carnous TM300.
These include four proline transport systems;
three glycine betaine transporters; one multi-
component transporter for choline, glycine
betaine, and carnitine; and one system for the
choline uptake (Rosenstein et al. 2009 ).Acid Production
Sugars (glucose and occasionally lactose or
sucrose) are usually included in the industrial
manufacture of fermented meat products,
though in Spain, chorizo is traditionally man-
ufactured with little or no added sugar.Two of the most common preservative
conditions employed in meat processing are
low temperatures and high salt concentra-
tions. L. sakei is remarkably well equipped
to cope with these conditions. It contains
several transporters for osmoprotective sub-
stances and has more cold stress proteins
than other lactobacilli. L. sakei has psychro-
trophic and osmotolerant properties, and is
able to grow at low temperatures and in the
presence of up to 10% sodium chloride
(NaCl). These physiological features are
associated with the presence in its genome of
a higher number of genes coding for stress -
response proteins, such as cold shock and
osmotolerance proteins, than found in other
lactobacilli. L. sakei lacks proteins involved
in adhesion to intestinal mucous, but its
genome codes for numerous proteins that
may be involved in adhesion to the meat
surface (e.g., to collagen), aggregation,
and biofi lm formation. Thus, the bacterium
seems well equipped to adhere to and spread
on a meat surface (Eijsink and Axelsson
2005 ).
Sanz and Toldr á (2002) reported an argi-
nine - specifi c aminopeptidase activity in L.
sakei that is important for the release of the
free amino acid, since it could be further
channeled into the arginine deiminase
pathway. The genes encoding the proteins
required for arginine catabolism in L. sakei
are organized in a cluster (Z ú r í ga et al. 2002 ),
and their transcription is repressed by glucose
and induced by arginine. Arginine, in par-
ticular, is an essential amino acid for L. sakei
and specifi cally promotes its growth in meat;
it is used as an energy source in the absence
of glucose (Champomier - Verges et al. 1999 ).
The concentration of free arginine in raw
meat is low, although it is relatively abundant
in muscle myofi brillar proteins. Moreover,
the genome analysis has shown that L. sakei
harbors a second putative arginine deaminase
pathway, containing two peptydil - arginine
deaminases, enzymes that can contribute to
the metabolism of arginine (Chaillou et al.