644 Part VI: Fermented Foods
flora, sometimes reinforced with backslopping,
which consists in the addition of a previous ripened,
fermented sausage with adequate sensory proper-
ties. However, this practice usually gave a high het-
erogeneity in the product quality. The use of micro-
bial starters, as a way to standardize processing as
well as quality and safety, is relatively new. In fact,
the first commercial use was in the United States in
the 1950s, followed by its use in Europe in the
1960s; since then, starters have seen extensive use.
Today, most of the fermented sausages are produced
with a combination of lactic acid bacteria, to get an
adequate acidulation, and two or more cultures to
develop flavor and facilitate other reactions, such as
nitrate reduction.
In general, microorganisms used as starter cul-
tures must satisfy several requirements according
with the purposes of their use: nontoxicity for hu-
mans, good stability under the processing conditions
(resistance to acid pH, low water activity, tolerance
to salt, resistance to phage infections), intense growth
at the fermentation temperature (i.e., 18–25°C in
Europe or 35–40°C in the United States), generation
of products with technological interest (i.e., lactic
acid for pH drop, volatile compounds for aroma,
nitrate reduction, secretion of bacteriocins, etc.), and
lack of undesirable enzymes (e.g., decarboxylases
responsible for amine generation). Thus, the most
adequate strains must be carefully selected and con-
trolled as they will have a very important role in the
process and will be decisive for the final quality. The
most important microorganisms used as starters
belong to one of the following groups: lactic acid
bacteria, Micrococcaceae, yeasts, or molds (Leistner
1992). The main roles and functions for each group
are shown in Table 28.3.
Lactic Acid Bacteria (LAB)
The most important function of lactic acid bacteria
consist in the generation of lactic acid from glucose
or other carbohydrates through either homo or het-
erofermentative pathway. The accumulation of lactic
acid produces a pH drop in the sausage. However,
some undesirable secondary products like acetic
acid, hydrogen peroxide, acetoin,... may be gen-
erated in the case of certain species having hetero-
fermentative pathways. L. sakei and L. curvatus
grow at mild temperatures being usual in the pro-
cessing of European sausages while L. plantarum
and P. acidilacticigrow well at higher temperatures
(30–35°C) closer to the fermentation conditions in
the sausages produced in the United States. Lactic
acid bacteria also have a proteolytic system, consist-
ing in endo- and exopeptidases, that contributes to
the generation of free amino acids during processing
and, most of them, are also able to generate different
types of bacteriocins with antimicrobial properties.MicrococcaceaeThis group consists of Staphylococcusand Kocuria
(formerly Micrococcus), which are major contribu-
tors to flavor due to their proteolytic and lipolytic
activity. Another important function consists in the
nitrate reductase activity, necessary to reduce nitrate
to nitrite and contribute to color formation and safe-
ty. However, these microorganisms must be added in
high amounts because they grow little or even die
just at the onset of fermentation, when low pH con-
ditions prevail. Preferably, low pH–tolerant strains
should be carefully selected. The species from this
family also have an important catalase activity that
contributes to color stability and, somehow, preven-
tion of lipid oxidation.YeastsDebaryomyces hanseniiis the predominant yeast in
fermented meats, mainly growing in the outer area
of the sausage due to its aerobic metabolism. D.
hanseniihas a good lipolytic activity and is able to
degrade lactic acid. In addition, it also exhibits an
important deaminase/deamidase activity, using free
amino acids as substrates and producing ammonia
as a subproduct that raises the pH in the sausage
(Durá et al. 2002).MoldsSome typical Mediterranean dry fermented sausages
have molds on the surface. The most usual are Peni-
cillium nalgiovenseand P. chrysogenum. They con-
tribute to flavor, through their proteolytic and lipoly-
tic activity, and to appearance, in the form of a white
coating on the surface (Sunesen and Stahnke 2003).
They also generate ammonia through their deami-
nase and deamidase activity and contribute to pH
rise. Inoculation of sausages with natural molds pre-
sent in the fermentation room is dangerous because