Members of the Micrococcaceae such as Micrococcus variansand
Staphylococcus carnosusare important with respect to the reduction of
nitrate to nitrite although this activity has also been demonstrated in
some lactobacilli. Their presence would not be required in nitrite-cured
products.
Sausage fermentations are conducted at temperatures ranging from
151 C up to in excess of 40 1 C, depending on the starter used, and last for
20–60 h. The relative humidity is also controlled to ensure that a slow
drying of the product commences. Acid production and the decrease of
the pH to below 5.2 promote the coagulation of meat proteins and this
aids moisture expulsion and development of the desired texture and
flavour. It also contributes to the microbiological stability and safety of
the product.
North American and northern European sausages are often smoked.
This confers a characteristic flavour but phenolic components of the
wood smoke also have important anti-oxidative and antimicrobial prop-
erties which improve shelf-life. Fungal growth may occur on the surface
of unsmoked sausages providing a particular character to these products
as a result of fungal lipolytic, proteolytic and antioxidative activity.
In the final drying stage which can last up to 6 weeks, the moisture
content is reduced further by storage at low temperatures, 7–15 1 C, and
at low relative humidity (65–85%).
The combination of antimicrobial hurdles or barriers introduced
during sausage fermentation is normally sufficient to ensure product
safety.Staphylococcus aureuswith its ability to tolerate reducedawand
pH and grow anaerobically would seem well suited to growth in these
products. Occasional outbreaks ofStaph.aureusfood poisoning have
been reported from the United States where higher fermentation temp-
arature are used. However, studies suggest thatStaph. aureusdoes not
compete well with the LAB present, particularly if the latter have a large
numerical superiority as a result of starter addition. The risk is also
reduced since enterotoxin production appears to be more susceptible
than growth to inhibition by adverse conditions (see Section 7.14.2).
Numbers of Salmonella and other Enterobacteriaceae have been
shown to fall throughout fermentation and drying. At present though,
our knowledge of such processes is insufficient to allow us to predict this
lethal effect reliably. It is therefore, most important that only good
quality raw materials are used so that undue reliance is not placed upon
these factors.
Outbreaks of Verotoxin producingE. coliin the United States asso-
ciated with fermented meats highlighted this problem and prompted the
US Food Safety and Inspection Service to recommend that the proce-
dures used in the production of ready-to-eat fermented products should
achieve a 5 log 10 cfu g^1 reduction in pathogen numbers.
Chapter 9 345