Carnimonas nigrificans and other microorganisms causing brown or black spots in fresh or cured meat products (hams, loins, pepperoni, sausage, ...) - Culture; Molecular diagnosis  (PCR)


Information 10/15/30.


The appearance of spots or dots, brown or black, in fresh or cured meat products is a result of the growth of microorganisms. Stains or spots, brown or black, in cured meat products (ham, loin, sausage, chorizo, ...) are located superficially, mainly in oily areas without affecting the muscle tissue and connective tissue, and without alter its smell or texture. The presence of these stains is an important from the point of view of consumer acceptance for factor. Several species of fungi have been considered responsible for the appearance of these black spots in meat products stored at low temperature (-1): Cladosporium cladosporoides, Cladosporium herbarum, Cladosporium oxysporum, Penicillium hirsutum and Aureobasidium pullulans. Also, several species of yeast, Yarrowia lipolytica as (Saccharomyces lipolytica before) and Candida zeylanoides, among others, have also been implicated.


Bacteria, Carnimonas nigrificans, was found responsible for the development of these spots, or black spots in cured meat products. Its development is favored by the addition of dextrose, maltose or dextrin, while inhibited by the addition of sodium nitrite or potassium bisulphite. Also we found other bacteria (Pseudomonas fluorescens) that can acquire black coloration under certain culture conditions in the laboratory, and that are likely to also be involved.


Curing some meat products, such as hams, it involves a process of maturation of 18 to 24 months with salt and cold to prevent the growth of microorganisms until the product is stabilized by reducing its water content. Finally, a ham, for example, reduce its pH to 5.6 to 6.5 and a value of 0.80 or less water. Under these conditions the growth of microorganisms is not favored. However, when the ripening process does not develop properly, or pH levels or adequate water are achieved, microorganisms which cause product degradation can develop, alter its appearance or organoleptic characteristics, with the consequent rejection consumer and economic loss for the processing industry.


Among bacteria, the main cause has been found Carnimonas nigrificans, but they have also found other bacteria such as Pseudomonas fluorescens. To prevent its development, it is important to control the conditions of curing and preservation after the ripening process, maintaining at 5 ° C, until essentially its content in surface water is reduced to less than 0.92, and its salt content is 2 %, as even with salt concentrations of 2 and 5% to 5 or 25, may develop black spots producing bacteria if the water content is 0.94 to 0.97.


However, yeasts and molds can survive and develop in refrigerated meat in air and in vacuum packed meat, can also develop when the transmission rate of oxygen through the wrapper is high. Yeasts and molds require oxygen to grow, and can do so from temperatures below 0 ° C to 40 ° C, depending on the species, so that tolerate and develop refrigeration temperature. Most tolerate little activity (presence) of water and prefer a slightly acidic environment with pH from 4.4 to 5.5. For these reasons, the measure used to prevent the development of bacteria in hams, does not prevent the development in other types of sausage, such as salami or sausage, and contamination of meat or casings used should be avoided with yeast or molds.


Tests in IVAMI:


  • For bacteria and / or fungi (yeasts and molds).
  • PCR for bacteria and / or fungi (yeasts and molds).
  • Identification of bacteria and / or fungi (yeasts and molds) by sequencing.


Recommended sample:


  • Meat product with black spots.


Preservation and shipment of sample:


  • Refrigerated (preferred) for less than 2 days.
  • Frozen: over 2 days.


Delivery term:


  • Culture for isolation: 4 working days.
  • Molecular targets for PCR: 48 to 96 hours.


Cost of the test: