The production of fermented meat, such as French saucisson sec, Spanish chorizo, or Italian salami, is an age-old process originally used to preserve raw meat, which is a highly perishable foodstuff. Controversially, the consumption of fermented meats is now associated with colon cancer, cardiovascular disease, and obesity, and discouraged by the World Cancer Research Fund. Scientific data suggest that these health risks could be bypassed by a more careful selection of the microorganisms responsible for the fermentation.

In industrial processes, a fermented sausage is the result of the interaction between the added “curing salts” and the microorganisms added as starter cultures. Curing salts are commonly used as sausage ingredients under the form of sodium or potassium nitrate to improve food safety as well as to stabilize the colour by preventing the meat to turn grey over time. The added microorganisms include two different groups of bacteria: lactic acid bacteria and coagulase-negative staphylococci (CNS). Whereas the lactic acid bacteria produce the  acidity of the fermentation (as they also do, for instance, in yoghurt), the CNS transform the curing ingredients to nitrite and nitric oxide, hereby yielding N-nitroso compounds. As a result of these chemical reactions, the growth of harmful bacteria is inhibited, in particular pathogens such as Clostridium botulinum and Listeria monocytogenes. Nitric oxide is a central molecule because it also guarantees the development of the cured red colour in the meat by generating a stable pigment called “nitrosomyoglobin”.  Yet, the N-nitroso compounds formed may be connected to cancer development when present in the digestive system.

A careful selection of meat-associated microorganisms may offer innovative processing alternatives.  These bacteria, in particular the ones from the heterogeneous group of CNS, could lead to the generation of clean-label products, compensating for the colour and safety problems that are encountered in the absence of curing salts.

Furthermore, a market trend for “clean” and “organic” labelling is breaking through and manufacturers are looking for alternatives for nitrate and nitrite which still preserve the colour, flavour, and shelf life of fermented meat. “Natural curing”, which is the use of vegetable sources that are naturally rich in nitrate and nitrite, such as celery power, have potential, but are merely pseudo-solutions because they consist basically of adding the same curing agents in a masked manner.

Can functional starter cultures lead to safe products with a stable colour in the absence of curing salts?

A recent PhD study at the research group of Industrial Microbiology and Food Biotechnology investigated 86 strains of meat-associated coagulase-negative staphylococci (CNS). Only one strain was able to synthesise nitric oxide in the absence of nitrate and nitrite. It was doing so by using the amino acid arginine, but was only displaying this activity in the presence of oxygen. This remains problematic as oxygen concentrations in fermented meats are usually low. Furthermore, this particular strain (Staphylococcus haemolyticus G110) belongs to a species that might be unsuitable for application due to potential safety concerns in human consumption. Therefore, arginine-derived nitric oxide production by CNS, although theoretically possible, meets several important constraints.

When curing salts that inhibit harmful bacteria are left out the meat recipe, natural antimicrobials might be valuable. This study indicated that Staphylococcus sciuri I20-1, which produces a natural antimicrobial, is capable of inhibiting the food pathogens Staphylococcus aureus and Clostridium botulinum. Nevertheless, the emergence of a resistant population of the pathogens suggested that this approach needs further investigation. The use of a combination of strains with complementary antimicrobial effects could for instance offer a possibility.

To conclude…

When looking for suitable microorganisms for meat fermentation, it is fundamental to ensure that the selected strains are indeed able to withstand the harshness of the processing conditions (e.g., the fermentation temperature, the degree of drying, the oxygen levels in the core of the product, etc…), so that they can successfully express their functional behaviour within the fermented meat product. In the case of fermenting sausages, the search for safe and suitable microorganisms continues.