206 Chapter 10
inosine hydrolase, and nucleoside phosphor-
ylase, all of which enable the release of a
ribose moiety from nucleoside (adenosine
and inosine) and its subsequent metabolism
(Chaillou et al. 2005 ). Moreover, the pres-
ence of methylglyoxal synthase, a novel
genetic trait in lactic acid bacteria, has been
proposed as a pathway to counteract frequent
glucose starvation and modulate the metabo-
lism of alternative carbon sources (Chaillou
et al. 2005 ).
The effect of environmental challenges on
the growth and acidifi cation kinetics of L.
sakei in sausages has been recently studied
by H ü fner and Hertel (2008). In this study, it
was demonstrated that L. sakei improves
its acidifi cation performances if cells are
exposed to sub - lethal stresses, such as cold
and osmotic shocks. This adaptation to stress
improves the performance of L. sakei during
sausage fermentation.Catalase Activity
The metabolism of most lactic acid bacteria,
such as the adventitious lactobacilli that con-
taminate raw meat, could lead to the forma-
tion of hydrogen peroxide, a compound that
interferes with the sensorial properties of
meat products, as it is involved in discolor-
ation of nitroso - heme pigment and lipid oxi-
dation. Bacterial strains used in meat cultures
can produce catalase, antioxidant enzymes
that cause disproportionate levels of hydro-
gen peroxide compared with oxygen and
water, preventing the risk of reduced quality
in the fermented meat. Thus, catalase produc-
tion is considered a relevant technological
property of starter cultures for fermented
meat products (Leroy et al. 2006 ). Production
of this antioxidant enzyme is a common trait
in aerobic bacteria, such as CNS. The char-
acterization of catalase and superoxide dis-
mutase in S. carnosus and S. xylosus has been
reported. The catalase gene kat A of S. xylosus
has been studied in detail (Barri è re et al.
2001a, b, 2002 ). Transcriptional activity ofDuring fermentation and ripening, LAB
convert glucose (their primary energy source)
to lactic acid, which is the main component
responsible for the pH decrease. This acidifi -
cation has a preservative effect, due to inhibi-
tion of pathogenic and spoilage bacteria with
little resistance to low pH, and it contributes
to the development of the typical organolep-
tic characteristics of the fermented sausages
(Bover - Cid et al. 2001 ). Although it is well
established that fermentable carbohydrates
have an infl uence on fl avor, texture, and yield
of fermented sausages, carbohydrates for use
in dry sausages formulations are generally
chosen to ensure an adequate initial drop in
meat pH (Bacus 1984 ; L ü cke 1985 ) for pres-
ervation reasons, and less importance is
given to the product texture. The level of
acidifi cation and the selection of the starter
culture to be used depend on the desired sen-
sorial properties of the product. In northern
European sausage technologies, more acid
products are preferred, obtained by adding
Lactobacillus starter cultures and more car-
bohydrates to the sausage matrix (0.6% –
0.8%). On the other hand, less acidic products
are obtained using a lower concentration of
glucose and also by using Staphylococcus
starter cultures, as occurs in typical southern
European fermented sausages. In these last
products, which are characterized by a longer
ripening period (up to 60 days), an increase
of pH occurs in the later stages of fermenta-
tion, related to ammonia release from ATP
and amino acid metabolisms.
Acidifi cation could also be the result of
alternative pathways. In L. sakei , the pres-
ence of genes involved in the energetic catab-
olism of nucleoside, such as adenosine and
inosine, is an example of the adaptation of
this organism to the meat environment.
Glucose, the favorite carbon source of L.
sakei , is rapidly consumed in meat, while
adenosine and inosine are abundant, reaching
twice the concentration of glucose. In addi-
tion (as shown in Fig. 10.1 ), L. sakei harbors
genes coding for adenosine deaminase,