Microbial Growth In Fermented Sausages Biology Essay

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Definition of Fermented Sausages: Fermented sausages can be defined as a mixture of mainly meat, fatty tissue, curing agents, salt, nitrite, sugar and spices, filled into casings and left for a fermentation or ripening process to take place, before dried. (FAO 1985)

Fermented Sausages Ecosystem:

Fermented sausage products are made with different kinds of meat as well as by different production technologies. The best meat that may be used to prepare sausages is that from adult animals, especially beef or pork. Both of these contain high levels of myoglobin, a protein found in the muscle cells, which has the ability to offer remarkable colour to the production of dry and semi-dry fermented sausages. Other criteria have to be considered when selecting meat for making sausages, such as pH value (the degree of acidity or alkalinity) and the composition and binding properties. Moreover the fat has to be fresh, white and with low polyunsaturated fatty acid.

While sodium chloride (NaCl) is always added to the production of fermented sausages at levels between 2.5% and 4%, other additives such as nitrate and nitrite are used at levels ranging from 150 to 250 ppm (parts per million to water), depending on the regulations of the country (Honikel, 2008). Sugars usually used for the production of fermented sausages are sucrose, dextrose, lactose and glucose. Out of these, the most important sugar, which is always used in the dry fermented sausages, is lactose. In addition, some spices are used in the manufacture of fermented sausages such as garlic, pepper and paprika.

In summary, the production of dry fermented sausages is based on three phases:

The combination of chopped meat blended in with other ingredients such as salt, nitrite or nitrate, sugar and spices.

The mixture is put into casings, followed by the fermentation process.

Finally the ripening and drying is completed.

However, two microbial reactions (interdependently and simultaneously) will also happen through the period of fermentation.

The reduction in the pH levels throughout glycolysis by lactic acid bacteria as well as the creation of nitric oxide causes a reduction of pathogens like (CNC) coagulase-negative cocci, including Micrococcus and/or Staphylococcus aureus.

Some additives such as sugar, sodium chloride, nitrite/ nitrate and the presence of intrinsic factors such as water activity (0.85 - 0.92) and extrinsic factors such as the level of temperature (24-300C to 12-18 0C) throughout ripening, will intensively select the microbiota which have the ability to improve in this ecological niche.

There are several species of lactic acid bacteria used in traditional fermented sausages, such as Lactobacillus plantarum, L.curvatus, L.sakei and Pediococcus spp. The latter are the most important species, usually isolated among lactic acid bacteria because they have the ability to adapt in severe conditions.(Mozzi et al. 2010)

Classification of Fermented Sausages:

The classification of fermented sausages depends on a range of criteria like water activity value (aw), moisture content, (M: P) moisture protein ratio, comminution degree of fat and meat and weight loss. The water activity value is the basis of distinguishing dry and semi-dry fermented sausages (Incze 2004). The final water activity value can be determined by the combination of the initial moisture protein and moisture in the salt content, as well as by the period of drying. On the other hand, the moisture protein ratio has the ability to give information in relation to the extent of dryness of the meat. On this basis, the final content of the moisture protein ratio should be 2.0 to 1 and the final water activity values between 0.90 and 0.91 or less; these rates should be used as the borderline for the manufacture of semi-dry and dry fermented sausages. The considerations of these parameters are important for establishing the shelf-life and safety of the product for consumption. (Toldrá 2010)

Types of Fermented Sausages:

Dry Sausages (Slow Fermentation)

Dry fermented sausages can be defined as ground meat or a class of chopped meat products that, as a result of microbial accumulation (LAB), reach a pH of 5.2 to 5.8 or less. This type of sausage is considered to be safer than others as result of a long drying process (3 to 4 months) at a low temperature (12 to 16 0C) with optional cold smoke. It has a final water activity aw range of 0.88 and about a 30% weight loss. Just a small quantity of sugar is used in this type of processing, about (0.1 to 0.3). The pH will decrease slightly and slowly. (Marianski. S, Marianski. A 2009), as result of the content of lactic acid, ranging from 0.5 to 1.0, which is lower than in semi-dry sausages. The moisture content is less than 30% with a moisture protein range of between 2.3 and 1. (Toldrá 2010).

The curing process is always applied in the dry fermented sausage especially before the lactic acid cultures are added; if the starter cultures have been added, the curing process will not occur. After the curing process, the ingredients of the sausage are stuffed into casings and then placed in a fermentation chamber. The acidity of the meat will increase gradually as a result of the metabolism of sugar by the lactic acid bacteria. The continuous drying process in collaboration with the acidity of the meat generates an environment hostile to harmful bacteria and preventative of its growth. (Marianski. S and Marianski. A 2009)

Meat and fat selection at (40C)

Mixing at (8-120C) in the absence of air


Fermentation at 16-200C, 3-8days

Smoking (optional)

Heating (optional)

Drying (12- 160C for 6-8weeks

Packaging for retail distribution

figure1. Flow diagram of the process of dry fermented sausage adapted from (pp. 53) (Marianski S and  Mariañski A 2009)

Semi-Dry Sausages (Medium or Fast Fermentation)

Semi-dry fermented sausages are a ground meat product or chopped meat that, as result of lactic acid bacteria action and the content of lactic acid ranging between 0.5% and 1.3%, reaches a pH of (4.8- 5.3). The main method used for this type of fermentation is acidification to drop the pH level however, it is important to add dextrose (glucose) to the ingredients of sausages, to support a fast pH drop. The smoking as well as cooking process for semi-dry fermented sausages takes place in the smokehouse with the heat at 60 0C. After the smoking process, the sausages might require drying for a short time.

The water activity values of the final products are ranged between (≥0.90 and 0.91), which is much higher than dry fermented sausages and the weight loss of these products is approximately 15 to 20%. (Toldrá 2010)

The fermentation process in the production of semi-dry sausages can be made in two ways; by adding the starter culture direct or by using the traditional way.

On the one hand, fast fermented sausages require about one to two days of fermentation time to drop the level of pH to (4.8). On the other hand, medium fermented sausages require two to three days of fermentation time to drop the pH to (4.8 to 5). In fact, these times of fermentation processing are based on the starter cultures that are used. There are several important factors that should be considered during the manufacture of semi-dry fermented sausages, such as the quantity and type of sugar used, fermentation temperature and additional additives like citric acid as well as GdL. (Marianski. S, Marianski. A 2009)

Meat and fat selection at (40C)

Mixing at (8-120C) in the absence of air

Stuffing (under vacuum)

Fermentation at 25-30 0C, 1-2days. RH 70-95%

Drying 5- 160C for 2-40 days

Smoking at 22- 60 0C

Packaging curried out under modified atmospheres or vacuum


Figure2. Flow diagram of the processing of semidry fermented sausage adapted from (pp.385) (Toldrá 2010)

Water Activity in the Dry and Semi-Dry Fermented Sausages:

All microorganisms including bacteria, viruses, moulds and yeasts require water to grow and multiply and the availability of this water for them is defined as water activity. (Marianski S and Mariañski A 2010).

According to the Food Agriculture Organization of the United Nations, the term of water activity has been defined in the manufacture of dry fermented sausages as the quotient of the vapour pressure present in the meat and the saturation vapour of the pure water at the same temperature.

(ps / po )

The water activity (aw) value in traditional manufacture of dry and semi-dry fermented sausages is decreased by smoking, drying and/or the curing process by adding some preservatives such as salt, sugar and spices. The salt, water and fat contents of the sausage also have a direct effect on the state of (aw). By adding one per cent of salt, or sodium chloride (NaCl) the water activity value can be reduced by 0.0060 and one per cent of fat reduces about 0.00045 of the water activity value. In the same manner, the addition of 1 per cent of sugar can reduce the (aw) value by about 0.0025, whereas the addition of soy protein reduces the water activity level by between 0.0012 and 0.0013. Ingredients used for making sausages include meat with 30 per cent of fat, mixed with 2 per cent sugar, 3 per cent of sodium chloride and 2 per cent of soy protein. The initial level of water activity in the primary product of lean meat, of 0.99 is then reduced to 0.9521 by these additives, while the water losses by evaporation and the heating degree control the final water activity. In addition the multiplication of yeast as well as bacteria can be inhibited at water activity value below 0.88 to 0.90, (Food and Agriculture Organization, 1985).

Figure3. Minimum water activity values for the growth of microorganisms

Hazards of Pathogenic Bacteria that have to be Controlled in the Dry and Semidry Fermented Sausages Production:

Escherichia Coli:

The strains of verotoxigenic E. coli including different serotypes like O157: H7, O103: H25 and O26 : H11. These serotypes have the ability to occur in the dry fermented sausages even with low (aw) values as well as low pH level, and the caused outbreaks of these serotypes in the dry fermented sausages were occurred in many countries.

(Heir et al 2010)

However, the most common serotype of (VTEC) occurs in the dry fermented sausages is E. coli O157: H7 and the first caused outbreak relating to E. coli O157: H7 in dry and semidry sausages was reported in 1994; 17 individuals consumed these products.

It is important bear in mind that the process of dry fermented sausages is able to reduce in viability of E. coli O157: H7 at level ≥ 5log CFU/g. On the other hand, some additives such as sinapis alba mustard and Brassica juncea mustard have ability to eliminate E. coli O157:H7 in the dry fermented sausages because they contain high levels of glucosinotates. (Luciano et al 2010).

Staphylococcus Aureus:

Staph. aureus has ability to cause food poisoning by producing toxins in meat (enterotoxin). It also has ability to grow in wide range of temperatures, between 7 to 460C and can grow at pH levels 4.5 to 9.3 (the optimum pH level is 7). Moreover, it has ability to grow at low aw values and 0.86 of aw has been considered the minimum level for growth. The optimum value of aw is considered to be ≥ 0.90 and the production of enterotoxin can be produce at aw value 0.87. (Lowley et al 2008).


The Enterobacteriaceae of salmonella has a wide distribution on meat. There are several factors that can encourage the growth Salmonella in the dry fermented sausages such as, high level of pH, high (aw) value, high temperatures through the ripening process and low levels of lactic acid. In many types of sausages, salmonellosis can result in outbreaks. For example, in Germany, the spreadable sausage was contaminated with salmonella due to high level of aw, a small amount of GdL and a little amount of sugar was added to the production and The purpose of this process to retain the meaty taste, as well as fresh consistency of the product. (Lund et al 2000).