185Chapter 9
Fermentation: Microbiology and Biochemistry
Spiros Paramithiotis , Eleftherios H. Drosinos , John N. Sofos , and
George - John E. Nychas
Introduction
Meat fermentation has been the subject of
intensive study over the last decades. It has
been early recognized that the development
of a proper ecosystem is a prerequisite in
order to address safety and organoleptic, as
well as nutrition - related, issues. The estab-
lishment and application of new molecular
tools has provided new insights that have led
researchers to more comprehensive under-
standing regarding both the microbial dynam-
ics and the biochemical changes that occur
during the development of this ecosystem. In
this chapter, an update concerning the eco-
system of spontaneously fermented sausages,
the biochemical changes during ripening, and
the development of starter cultures is pro-
vided, as well as nutritional and public health
aspects.
The Spontaneously Fermented
Sausage Ecosystem
Spontaneously fermented sausage production
includes mixing of minced meat and fatty
tissue with curing agents, carbohydrates, and
spices; stuffi ng into casings; and ripening,
which can be further subdivided into fermen-
tation and aging. Variations in the type and
amount of raw materials, fermentation, and
drying conditions lead to an extended diver-
sity concerning the dominating microbiota,
giving rise to a wide range of products with
unique sensorial traits.
The microbiota of batter freshly stuffed
into casings is dominated mainly by microor-
ganisms present in the raw materials, with
raw meat and casings being their major
source (Comi et al. 2005 ; Lebert et al. 2007 ).
As a result, pseudomonads and members of
the Enterobacteriaceae family may reach
levels as high as 10^5 and 10^4 cfu g^ −^1 , respec-
tively (Drosinos et al. 2005 ; Lebert et al.
2007 ). The presence of pathogens, such as
Escherichia coli , aerobic spore formers,
Staphylococcus aureus , and Listeria monocy-
togenes , has also been reported (Samelis
et al. 1998 ; Comi et al. 2005 ; Chevallier et al.
2006 ). On the other hand, lactic acid bac -
teria, Gram - positive catalase - positive cocci,
enterococci, and yeasts - molds are usually
present at populations lower than 10^5 cfu g^ −^1.
During ripening and as the water activity is
reduced to 0.96 – 0.97 and the oxygen con-
sumed, a shift in the microbiota composition
toward lactic acid bacteria and Micrococcaceae
takes place (Luecke 1998 ). By the end of
ripening — depending upon the raw materials,
ripening conditions, and hygienic parame-
ters — the microecosystem usually consists
of 10^7 – 10^9 cfu g^ −^1 lactic acid bacteria, 10^4 –
10 6 cfu g^ −^1 Micrococcaceae and enterococci,
and 10^2 – 10^4 cfu g^ −^1 yeasts - molds.
Apart from composition, microbial
dynamics has also been a fi eld of extensive
study, especially over the last decade with the
advancement of new molecular tools, in par-
ticular the ones based on the polymerase
chain reaction (PCR). The availability of