208 Chapter 10
The pattern of the proteolysis in fermented
sausages is infl uenced by several variables,
such as product formulation, processing con-
dition, and starter culture (Hughes et al.
2002 ). The volatiles so far recognized as
being produced by staphylococci are primar-
ily amino acid catabolites, piruvate metabo-
lites, and methylketones from incomplete
β - oxidation of fatty acids (Stahnke et al.
2002 ). In particular, S. xylosus and S. carno-
sus modulate the aroma through the con-
version of amino acids (particularly the
branched - chain amino acids BCAA: leucine,
isoleucine, and valine). The BCAA can be
degraded into methyl - branched aldehydes,
alcohols, and acids by S. xylosus and S.
carnosus (Vergnais et al. 1998 ; Larrouture
et al. 2000 ; Beck et al. 2002 ). Furthermore,
addition of S. carnosus starter culture has
been shown to decrease the maturation time
of Italian dried sausages by more than two
weeks (Stahnke et al. 2002 ). Olesen et al
(2004) reported that curing conditions had a
considerable infl uence on the development of
volatile compounds in sausages. In addition,
major differences were observed in the
development of volatile compounds, depend-
ing on whether S. xylosus or S. carnosus were
used as starter culture.
Even though microbial proteolytic activity
is generally low in the conditions found in
fermented sausages (Kenneally et al. 1999 ),
a minor, strain - dependent activity may still
partly contribute to initial protein breakdown
(Molly et al. 1997 ; Fadda et al. 1999a, b,
2002 ; Sanz et al. 1999 ). Several studies lead
the hypothesis that both endogenous and bac-
terial peptidases are required for complete
hydrolysis of oligopeptides, and the activity
of these enzymes could be strongly involved
in the quality of the fi nal product (Rodr í guez
et al. 1998 ; Fadda et al. 1999a, b ; Mauriello
et al. 2002, 2004 ; Casaburi et al. 2005 ;
Drosinos et al. 2007 ). It has been described
in vitro that several Lactobacillus spp. exhibit
proteolytic activity on porcine muscle myo-
fi brillar and sarcoplasmic proteins. Fadda
et al. (2001a) reported the contribution ofA summary of the main metabolic path-
ways used by the meat starter bacteria
( Lactobacillus and Staphylococcus ) is given
in Figure 10.1.
Nitrate Reduction
Nitrate is added to fermented sausages for its
capacity to obtain and fi x the typical color of
cured products, rather than for its antimicro-
bial properties. To be effective, the added
nitrate must be reduced to nitrite. Besides
contributing to fl avor, Staphylocuccus and
Kocuria also have a role because of their
nitrate reductase and antioxidant activities
(Tal ó n et al. 1999, 2002 ). These microorgan-
isms reduce nitrate to nitrite, which is impor-
tant for the formation of nitrosylmyoglobin,
the compound responsible for the character-
istic red color of fermented meats. The nitrate
reductase activity is widespread in CNS; it
has been detected in S. xylosus , S. carnosus ,
S. epidermidis , S. equorum , S. lentus , and S.
simulans (Tal ó n et al. 1999 ; Mauriello et al.
2004 ). In S. carnosus , the molecular genetic
determinants for nitrogen regulation, the
nre ABC genes, were identifi ed and shown to
link the nitrate reductase operon ( nar GHJI)
and the putative nitrate transporter gene
nar T. The data provide evidence for a global
regulatory system, with oxygen as the effec-
tors molecule (Fedtke et al. 2002 ). The high
dissimilatory nitrate respiration, typical of S.
carnosus and involved in nitrate reduction in
meat products, was found to be present in the
genome of S. carnosus TM300 (Rosenstein
et al. 2009 ).
Flavor Formation
The fl avor and aroma of fermented meats is
a combination of several elements. Lactic
acid bacteria produce lactic acid and small
amounts of acetic acid, ethanol, and acetoin;
however, to ensure the sensory quality of
fermented sausages, the contribution of the
proteolytic and lipolytic activities of staphy-
lococci is fundamental.