202 Chapter 10
the compostition of some commercial starter
cultures.
Lactic Acid Bacteria
The genus Lactobacillus is of great impor-
tance in meat fermentation, and for this
reason, species of this genus are frequently
used as starter cultures in sausage and cured
meat production. The genus Lactobacillus
includes more than 150 different species,
with a large variety of phenotypic, biochemi-
cal, and physiological traits (Axelsson 2004 ).
The diversity and complexity of Lactobacillus
genus is refl ected by the presence of three
phylogenetic groups: the L. casei subgroup,
containing the facultative heterofermentative
lactobacilli; the Leuconostoc group, which
encompass the obligate heterofermentative;
and the L. acidophilus group, composed of
obligate homofermentative lactobacilli.
Only a limited number of Lactobacillus
species is commonly isolated from meat fer-
mentations and used as starter cultures.
Among them, L. sakei , L. curvatus and L.
plantarum , belonging to the sub - group of
facultative heterofermentative lactobacilli,
are generally used for this purpose. The main
energetic metabolism of these bacteria is the
dissimilation of sugar to organic acid by
means of glycolysis and phosphoketolase
pathways. When hexoses are the energy
source, lactic acid is the major fermentation
end product. Several studies clearly demon-
strated that L. sakei is the predominant
species in fermented meat products, and its
use as a starter culture for sausage production
is widespread (Leroy et al. 2006 ).
The fi rst complete genome sequence of
bacteria from meat fermentation was that of
the sausage isolate L. sakei 23K (Berthier
et al. 1996 ). Its 1.88 - Mb chromosome, which
encodes 1,883 predicted genes, harbors the
genetic determinates for a specialized meta-
bolic repertoire that refl ects the adaptation to
meat fermentation (Chaillou et al. 2005 ). The
intra - specifi c diversity of L. sakei species has
been investigated (Chaillou et al. 2008 ) by
analyzing the genomic variations. This study
revealed that L. sakei strains show extensive
differences in chromosomal size, which
range from 1.8 to 2.3 Mb. Cluster analysis
revealed that there are ten different strains
clusters, comprising two main groups of
strains: L. sakei subsp. carnosus , the more
diverse, comprised of seven clusters; and L.
sakei subsp. sakei , comprised of three
clusters.
L. sakei has evolved to adapt itself to the
meat environment, harboring the genetic
function that gives it the ability to grow and
survive there. L. sakei seems very well suited
to derive energy from other compounds
that are more abundant in meat. Its adaptation
to meat, an environment rich in amino
acids because of the activity of endogenous
proteases, has caused it to lose biosynthetic
pathways for amino acid synthesis. L. sakei
is therefore auxotrophic for all amino
acids except aspartic and glutamic acid
(Champomier - Verges et al. 2002 ). Amino
acid metabolism can provide an alternative
energy source for L. sakei when glucose
is exhausted, and this affects the sensorial
properties of the sausage, as discussed
later. The genome shows a particularly well -
developed potential for amino acid catabo-
lism, and in addition, L. sakei has the ability
to use purine nucleosides for energy produc-
tion (a unique property among lactic acid
bacteria).
Although L. plantarum has been identifi ed
as part of the meat microbiota and is used as
starter cultures for meat fermentation, this
species lacks the specifi c adaptation to meat
environment found in L. sakei. L. plantarum
is a highly versatile bacterium, frequently
encountered in a variety of different environ-
ments, such as vegetable and dairy fermen-
tation and the gastrointestinal tract of
warm - blooded animals. The metabolic and
environmental fl exibility of this organism is
refl ected by the size of its genome, 3.3 Mb
(Kleerebezem et al. 2003 ), which is the