The fermentation step in sausage production involves the action of a lactic acid bacterium on the sugar added to ground meat. This organism, generally a strain of Pediococcus cerevisiae added as a starter culture, ferments the sugar to lactic acid. The acid causes the meat to develop the characteristic texture associated with sausage. The flavor of sausage is due to the lactic acid, other byproducts of bacterial fermentation, salt, seasonings and nitrite. Salting also affords protection against many spoilage organisms.
Most sausage formulas include sodium nitrite (NaNO2) as a curing agent. The addition of nitrite to a meat product inhibits the growth of the pathogen Clostridium botulinum. Also, nitrite is responsible for the pink color associated with sausage and other cured meats, such as bologna and ham. Third, a nitrite cure adds a particular flavor to the sausage.
In rare instances, sodium nitrate (NaNO3) is added during manufacture rather than sodium nitrite. One then relies on bacteria in the meat to reduce the nitrate to nitrite. It is more difficult to control the concentration of nitrite in a sausage by the use of this method. On occasion, excessive nitrate reduction will take place, resulting in overly high concentrations of nitrite in the product. The excessive amount of nitrite, in the presence of the lactic acid, will cause severe oxidation of the meat pigment (myoglobin), producing a green pigment (oxymyoglobin). This form of greening of cured meats is referred to as nitrite burn.
A second form of greening results from the accumulation of hydrogen peroxide on meats. Lactics on the surfaces of meats will, in the presence of atmospheric oxygen, produce hydrogen peroxide if they are allowed to grow. Meat must therefore be handled appropriately, keeping initial lactic counts low and avoiding temperature abuse to preclude growth of these organisms and subsequent greening of the meat. Lactobacillus viridescens is commonly associated with peroxide greening of meats.
In this exercise, sausage will be prepared, using both a straight nitrite cure and also an excessive nitrate cure to induce nitrite burn. In the latter case, a nitrate-reducing strain of Staphylococcus will be added. Sausage prepared with the use of a starter culture (Pediococcus) will be compared with that prepared with a "wild fermentation." In addition, the effects of greening by nitrite and hydrogen peroxide on sliced, packaged bologna will be demonstrated.
