Probiotic Meat Products

1. Introduction

The growing concern of consumers regarding the food health and safety issues has led to the development of products that promote health and well-being beyond its nutritional effect [1]. Functional foods are those which promote beneficial effects to human´s health beyond nutrition. Their effects are due to the addition of active ingredients, the removal or the replacement of undesirable compounds in its composition [2].

The marketing of food for health benefits began in 1960s. In 1970s the trend was to eliminate or reduce the harmful constituents like sugars and fats from food. In 1980s, the trend continued with the reduction or elimination of food additives, which led to the induction and addition of useful components like vitamins, minerals and probiotics in 1990s [1, 3].

Among the different types of functional food, probiotics represent a large share of the functional food market, being used mainly in dairy beverages, cereal products, infant feeding formulas, fruit juices and ice cream [4-7].

In meat industry, the demand for new products has greatly influenced its development, especially for sausage type products. However, lately, those meat products are considered unhealthy by a part of population because of their fat content and the use of additives and spices in their formulation. Therefore, the addition of probiotics to the fermented sausages could promote the health benefits associated with lactic acid bacteria and contribute to the increase in the consumption of such products [7, 8].

The use of probiotics seems more promising in raw fermented meat products like salami as they are made with raw meat and consumed without prior heating, which would kill the probiotic bacteria [9, 10]. However, the incorporation of probiotic bacteria to these products also represents a technological challenge because of the known sensitivity of probiotic to curing salts, spices and other ingredients used in the formulation of the fermented sausages [11]. Furthermore, this addition requires the use of microorganisms that are resistant to the fermentation process and that remain in a minimal viable number of cells to survive the stomach pH and exert beneficial effects in the intestines [8].

Additionally, the processing of probiotic meat products implies taking into account the appropriateness of the probiotic culture to the target consumer, the intestinal functionality expected for the probiotic species, the rate of survival of probiotic during food processing and the need of maintenance in the probiotic product of the same sensory attributes that characterize the regular product [8, 10, 12].

This chapter presents the potential applications of probiotics in fermented meat products, focusing on the technological challenges, the functional effects of probiotics and on the researches that address the addition of probiotics in fermented meat products.

2. Fermented meat as a probiotic product

2.1. Fermented sausages

Fermented sausages are defined as a mixture of ground lean meat and minced fat, curing salts, sugar and spices, which are embedded into a casing and subjected to fermentation and drying [6, 13, 14].

The quality of fermented sausages is closely related to the ripening process that gives color, flavor, aroma, and firmness to the product which are developed by a complex interaction of chemical and physical reactions associated with the fermentative action of the microbiological flora present in the sausage. In handmade production processes of fermented sausages, fermentation occurs spontaneously by the action of in nature bacteria present on meat. In industrial processes the microbiological flora, responsible for the fermentation process, is known as starter culture [6]. Starter cultures are defined as preparations containing live microorganisms capable of developing desirable metabolic activity in meat. They are used to increase the microbiological safety, to maintain stability by inhibiting the growth of undesirable microorganisms and to improve the sensory characteristics of fermented sausages [1].

Starter cultures are formed by mixing of different types of microorganisms, where each one has a specific function. Lactic bacteria are used in order to generate controlled and intense acidification which inhibits the development of undesirable microorganisms, and provides increased safety and stability to the product. On the other hand, coccus catalase positive type bacteria, as Staphylococccus and Kocuria, yeasts as Debaryomyces, and molds as Penicillium usually provide desirable sensory characteristics to the product [1, 2, 8].

Table 1 shows the microorganism species most commonly used as starter cultures to fermented meat products.

Microorganism	Genus and Species
Lactic acid bacteria	Lactobacillus acidophilus ^a, L. alimentarius^b, L. brevis, L. casei^a, L. curvatus, L. fermentum, L. plantarum, L. pentosus, L. sakei; Lactococcus lactis; Pediococcus acidilactici, P. pentosaceus
Actinobacteria	Kocuria varians^c; Streptomyces griséus; Bifidobacterium sp.^a
Staphylococcus	S. xylosus, S. carnosus subsp. carnosus, S. carnosus subsp. utilis, S. equorum^b
Halomanadaceae	Halomonas elongata^b(tested in dry cured ham)
Enterobacter	Aeromonas sp.
Mold	Penicillium nalgiovense, P. chrysogeum, P. camemberti
Yeast	Debaryomyces hansenii, Candida famata

Table 1.

Microorganism species most commonly used as starter cultures in fermented meat productsSOURCE: [15-17].^a Used as probiotic cultures.^b Used in commercial tests in industrial scale (Laboratorium Wiesby, Niebüll and Rudolf Müller and Co)^c formerly known as Micrococcus varians.

The selection of starter cultures for use in fermented meat products must be carried out according to the product formulation and the technological processing employed, since environmental factors can select a limited number of strains with the ability to compete and overcome on product. Typically, the species used as the starter culture are selected from strains naturally predominant in meat products and hence, well adapted to this environment. Therefore, these species present a tendency to have greater metabolic capacity which is reflected on the development of the proper sensory and physical-chemical characteristics on the product [6].

Given the adverse conditions of the meat matrix for a number of microorganisms, including those considered probiotics, several studies suggest the selection of probiotic properties in lactic bacteria from commercial starter culture traditionally used in fermented meat products and therefore, already adapted to grow in these conditions. These cultures will provide to the product the same sensory and technological characteristics than the traditional starter cultures, and exert beneficial effects to health [8, 15, 18]. Among the starter lactic acid bacteria, Lactobacillus brevis, L. plantarum, L. fermentum and Pedioccus pentosaceus have been characterized as probiotics [19-21]. Strains of L. sakei and P. acidilactici have also been proposed as potential probiotic in meat products, due to its survival under acid conditions and high concentrations of bile [22]. Probiotic cultures can also be selected from the lactic acid bacteria (LAB) naturally presented in fermented meat products [7, 21, 23-25].

2.2. Probiotic fermented sausages

Although the concept of including probiotics in meat products is not entirely new, only a few manufacturers consider the use of fermented sausages as vehicles for probiotics [7, 17].

Several meat products containing probiotics with claims for health benefits have been commercialized. A salami containing three intestinal LAB (Lactobacillus acidophilus, Lactobacillus casei and Bifidobacterium spp.) was produced by a German company in 1998. In the same year, a meat spread containing an intestinal LAB (Lactobacillus rhamnosus FERM P-15120) was produced by a Japanese company [26-28].

Fermented sausages are suitable for the incorporation of probiotic bacteria since mild or no heat treatment is usually required by dry fermented meat products, thus providing the suitable conditions required for the survival of probiotics [3, 14, 26]. The sausage has to be designed in such a way as to keep the number and viability of probiotic strain in the optimum range. Thus, reduction in pH (e.g. < 5.0), extended ripening (e.g. >1 month), dry or excessive heating has to be avoided if the beneficial effects of probiotic are to be harvested [3, 7].

In meat sector, meat cultures are generally added to fermented meat products with the function of inhibiting pathogens and increasing shelf-life, rather than introducing functional or physiological qualities. Those cultures are called protective starter cultures and do not promote significant changes in physical and sensory characteristics of the product. On the other hand, probiotic cultures are, by definition, those that after ingestion in sufficient number employ health benefits in addition to their nutritional effects [6, 8, 15]. However, often, the probiotic cultures have also been used in meat products as protective cultures, since both of these cultures have the ability to survive in adverse environments and to produce organic acids and bacteriocins [18]. Likewise, probiotics added to meat products are also known as functional starter cultures since they contribute to safety, can provide sensory and nutritional benefits and promote health [6].

The success of probiotics in other types of foods, especially dairy products, is based on scientific evidence of beneficial effects provided by some microorganisms. In meat products, the beneficial effects must be proven with the consumption of these products. From the good results obtained with dairy products it is not possible to conclude that a probiotic species will have the same effect on another type of product. This is due to the fact that the performance and properties of microorganisms are environment-dependent. Furthermore, there are few studies about the proper number of probiotic bacteria that should be ingested in meat products to achieve the desired effect [1, 15].

The estimated number of viable cells of probiotic bacteria to be ingested to obtain beneficial effects and temporary colonization of the intestine is around 10⁹ to 10¹⁰ CFU/ g of product, in accordance with the counts of 10⁶ to 10⁸ viable cells found in 1 g of feces. Therefore, in a fermented meat product containing 10⁸ CFU/ g, the minimum daily consumption might be 10-100 g of product [1, 29]. Rivera-Espinoza and Gallardo-Navarro [17] recommended the concentration of probiotic viable cells of at least 10⁸ to 10⁹ CFU/ g of the product to obtain the physiological effects associated with the use of probiotic food.

Despite the known health benefits provided by the use of probiotics such as the improvement of intestinal transit and digestion, improvement of symptoms of lactose intolerance, increase in immune response, reduction of diarrhea episodes, prevention or suppression of colon cancer and reduction of blood cholesterol [30, 31], much attention has paid to the use of probiotics in meat products in order to increase product safety and few studies evaluated the health benefits associated with the consumption of these products [7, 8, 15].

2.3. Most used probiotic cultures in meat products

Probiotics are mainly the strains from species of Bifidobacterium and Lactobacillus. Other than these, some species of Lactococcus, Enterococcus, Saccharomyces and Propionibacterium are considered as probiotics due to their ability to promote health in the host [32].

In fermented meat products several studies have demonstrated the feasibility of using probiotic Lactobacillus.

Arihara et al. [33] studied the use of Lactobacillus gasseri to improve the microbiological safety of fermented meat product. The use of Lactobacillus rhamnosus and L. paracasei subsp. paracasei for the fermentation of meat products has been studied by Sameshima et al. [9], while Pennacchia et al. [20] report the use of Lactobacillus plantarum and Lactobacillus paracasei as probiotics in meat products.

Erkkilä et al. [22] conducted experiments using probiotic strains of L. rhamnosus GG and potentially probiotic strains of L. rhamnosus LC-705, L. rhamnosus VTT-97800 and L. rhamnosus VTT for the manufacture of dry sausage.

Andersen [10] demonstrated the ability of mix of a traditional starter culture, Bactoferm T-SPX (Chr Hansen), and the potential probiotic cultures of L. casei LC-01 and Bifidobacterium lactis Bb-12 to ferment meat product.

Also Erkkilä et al. [11] used strains of Lactobacillus gasseri, L. rhamnosus, L. paracasei subsp. paracasei, L. casei and Bifidobacterium lactis for the manufacture of salami.

Pediococcus acidilactici PA-2 and Lactobacillus sakei Lb3 showed good survival characteristics in fermented sausages, being considered as probiotic candidates for meat products [7], as well as Lactobacillus casei and Lactobacillus paracasei isolated from fermented sausages which showed in vitro functional abilities [25].

Macedo et al. [34] investigated the viability of the use of probiotic Lactobacillus paracasei, L. casei e L. rhamnosus in fermented dry sausage with the maintenance of the technological and sensory characteristics of the product.

Vuyst et al. [7] and Khan et al. [3] stated that Lactobacillus species currently used as meat starter cultures, as L. plantarum and L. casei, can have a significant scope for being utilized in probiotic sausage manufacture.

2.3.1. Criteria for the selection of probiotic cultures for meat products

The criteria for a microbial culture to be considered probiotic are the stomach acidity resistance, lysozyme and bile resistance and the ability to colonize the human intestinal tract using mechanisms of adhesion or binding to intestinal cells [7, 8, 23, 35]. Other authors have also included the ability to tolerate pancreatic enzymes as a required characteristic of probiotic cultures [16].

Additionally to the criteria described above, the probiotic bacteria need to have GRAS (Generally Recognized as Safe) status [36]. Currently, this concept also includes the antibiotic resistance evaluated by Qualified Prediction Security Program suggested by EFSA (European Food Safety Authority). The ability of probiotic bacteria used in meat products to resist to some antibiotics can be genetically transmitted to other bacteria. Scientific studies report genetic determinants for bacterial resistance to chloramphenicol, erythromycin and tetracycline [14]. Normally, the lactic acid bacteria are sensitive to penicillin G, ampicillin, tetracycline, erythromycin, chloramphenicol and aminoglycosides, quinolones and glycopeptides [18]. Thus, the selection of probiotic cultures for meat products implies confirmation of the absence of antibiotic resistance transferable gens in selected strains [14].

However, among the criteria for the selection of probiotic cultures, the main condition to be evaluated is the ability of strains to promote beneficial effects in the host through interactions probiotic/ host and to prevent diseases [37]. These effects on human health may occur in three different ways according to the specificity of the strain: the antagonist action against other microorganisms in the same environment (by nutrient competition, bacteriocin production or competitive exclusion), the barrier effect on the intestinal mucosa and the boosting of immune system [7, 36].

2.3.2. Technological characteristics of probiotic cultures for meat products

For addition in fermented meat products, the probiotic bacteria need to maintain their viability towards the adverse conditions generated during the fermented sausages manufacture: low pH (<5.0), high salt content (2-3%), high nitrite content (around 120 ppm) and low water activity (<0.85). The probiotic cultures should also be capable of growing fast during the fermentation, be easily cultivated on an industrial scale, resist to freezing and lyophilization processes, provide longer shelf life to the product as well as contribute to the sensory quality of the final product [7, 11].

Probiotic cultures can be added in fermented sausage as part of the starter culture or as an additional culture incorporated during the mass mixing (Figure 1).

Figure 1.

Basic flowchart of the processing of fermented dry sausage with the addition of probiotic cultures

Probiotic cultures may be added to the sausage batter as liquid inoculum, in high concentrations, or lyophilized. However, the addition of lyophilized culture can delay the fermentation time and reduce the culture viability in the final product. These effects can be reduced with the culture microencapsulation prior to lyophilization. This procedure is also indicated when probiotic strains are inhibited by ingredients of the sausage composition [6, 38].

Microencapsulation increases the viability of bacteria due to the protective effect of a polymeric membrane formed around the bacterial cells. The methods used for microencapsulation of lactic acid bacteria are extrusion and emulsification. Extrusion produces microcapsules with 2-3 mm in diameter which are 60 times greater than the microcapsule formed by emulsification. The materials most commonly used for the microencapsulation of probiotics include alginate, starch, k-carrageenan, guar gum, xanthan gum, gelatin and milk whey proteins. Muthukumarasamy and Holley [38] tested the microencapsulation of Lactobacillus reuteri ATCC 55730 in alginate for use in fermented meat product and found no adverse effect on the sensory quality of the product. Despite the microcapsules were visible to naked eye, they were detected as fat particles by the panelists due to their size and color similarity.

Rivera-Espinoza and Gallardo-Navarro [17] encapsulated Bifidobacterium longum and Lactobacillus reuteri in alginate to increase the survival of probiotics in fermented meat. Recently, Poulin, Caillard, and Subirade [39] created succinylated β-lactoglobulin tablet to protect B. longum strain and proved its protection effect in-vivo and in-vitro. Heidebach, Först and Kulozik [40] reported higher viability of Lactobacillus F19 encapsulated with casein during freeze storage compared to Bifidobacterium Bb12. Furthermore, the same authors [41] microencapsulated these two strains with rennet-induced gelation of milk, obtaining higher yields and improved survival rates.

2.3.2.1. Lactic acid production

One of the most important characteristics of Lactobacillus in fermented meat products is the production of lactic acid. The acidification has positive effects on safety and on the sensory characteristics of the product. The pH decrease in fermented sausages provides the coagulation of myofibrillar proteins, resulting in the increase of firmness and cohesiveness of the final product, and contributes to the flavor and red color. Inhibition of spoilage and pathogenic microorganisms is also provided by the fast decrease of pH and lactic acid production in appropriate quantities. The fast decrease in pH values during fermentation of sausages can also contribute to the prevention of the accumulation of biogenic amines, which are harmful to health [14].

However, it is important to confirm that the lactic acid bacteria used as probiotic produce the L(+) isomer lactic acid and do not produce the D(-) isomer lactic acid, due to the higher inhibitory effect on undesirable microorganisms of the L(+) lactic acid. Moreover, the D(-) lactic acid form is not metabolized by the human body and may cause health problems in consumers [7, 14, 42].

2.3.2.2. Resistance to salt (NaCl) and nitrite (NO₂)

According to Arihara and Itoh [43] and Sameshima et al. [9], the addition of 3% sodium chloride (NaCl) and 200 ppm sodium nitrite (NaNO₂) to fermented sausage is mandatory in Japan in order to maintain the microbiological safety of the product. Thus, the use of cultures resistant to curing salts is the first condition for the production of sausage with probiotic properties [23].

Sameshima et al. [9] tested the resistance of 202 Lactobacillus species of intestinal origin to sodium nitrite and sodium chloride in liquid medium and found that strains of L. paracasei ssp. paracasei, L. rhamnosus and L. acidophilus were tolerant to these salts. Similar results were obtained by Macedo et al. [44] who found resistance of Lactobacillus rhamnosus, Lactobacillus paracasei and Lactobacillus casei to the simultaneous use of sodium chloride and sodium nitrite at the concentrations of 3% and 200 ppm, respectively.

2.3.2.3. Bacteriocin production in meat products

Bacteriocins are peptides or proteins produced by microorganisms which destroy or inhibit the growth of gram positive bacteria, in particular Listeria monocytogenes. The use of bacteriocin-producing cultures in meat products may represent a considerable benefit to the consumers health and safety of the product, since bacteriocins do not pose toxicological hazards arising from their consumption and act as a natural form of preservation in the products. The production of bacteriocins has been detected in several lactic acid bacteria isolated from meat products such as L. sakei, L. curvatus, L. plantarum, L. brevis and L. casei [6].

2.3.3. Physiological characteristics of probiotic cultures for meat products

2.3.3.1 Resistance to low pH

The tolerance to acidity and bile salts are two fundamental properties that indicate the ability of a probiotic microorganism to survive through the gastrointestinal tract, resisting the acidic conditions of the stomach and the bile salts in the initial portion of the small intestine [22, 45].

The acidity is considered the most important deleterious factor that affects the viability and growth of lactic acid bacteria, since its growth is greatly inhibited at pH lower than 4.5. Such inhibition is related to a reduction in intracellular pH of the bacteria caused by non-dissociated lactic acid form, which due to its lipophilic nature, it diffuses through the cell membrane and causes collapse of the electrochemical gradient, promoting bacteriostatic or bactericidal effects [14, 36].

The survival of the probiotic to the gastric juice depends on its ability to tolerate low pH. At the time of hydrochloric acid excretion, the stomach pH is 0.9, however, during the digestive process the pH increases to around 3 due to the presence of food, remaining under this condition for a period of 2-4 hours [1, 22].

Due to the sensitivity of most bacteria to the low pH of the stomach, probiotic bacteria have to be ingested with food, because it acts as a buffer on the high acidity of the stomach, allowing the survival of the bacteria during gastric transit [46]. Meat, as well as milk, has buffers characteristics in acid environment and can thereby protect the probiotic from the adverse environment of the stomach [1].

Erkkilä and Petäjä [22] reported the resistance of species of Lactobacillus pentosus, L. sakei, Pediococcus pentosaceus e P. acidilactici to low pH and observed that at pH 4 and pH 5, the number of viable cells of these species remained unchanged compared to its initial value, indicating that the growth of the cultures was not affected by low pH.

Taking into account the pH conditions of stomach and the digestion time, probiotic bacteria ingested with food must be capable of resisting pH value 3 for a period of 2-4 hours to allow their survival during gastric transit. Macedo et al. [44] found that Lactobacillus paracasei used in probiotic salami was able to resist and grow in a medium at pH 3, showing a 20% increase in the initial number of cells during the 4 hours of exposure to this acidic condition.

Pennacchia et al. [20] tested the resistance of Lactobacillus isolated from 10 different types of salami to low pH. The authors found that from a total of 14 lactic acid bacteria that survived at pH 2.5 during 3 hours, 5 belonged to the Lactobacillus casei group. These authors also mention studies on the resistance of 20 strains of Lactobacillus isolated from infant faeces to acidic conditions and report the high viability rate of 3 strains of L. paracasei and one of L. rhamnosus at low pH.

2.3.3.2. Resistance to bile salts

Bile plays an important role in intestinal defense mechanism. The intensity of its inhibitory effect on microorganisms is determined by the concentration of salts in the bile composition [47]. Bile salts act by destroying the lipid layer and the fatty acids of the cell membrane of microorganisms. However, some Lactobacillus strains are able to hydrolyze bile salts by excreting bile salt hydrolase enzyme that weakens the detergent power of the bile [23]. Lactobacillus bile resistance has also been associated with other factors such as the stress response system as well as with the elements that involve the maintenance of cellular wall integrity, the energetic metabolism, the amino acid transport and the fatty acid biosynthesis [48].

According to Erkkilä and Petaja [22] and Pennacchia et al. [20], the average concentration of bile salts in the human intestinal tract is 0.3%, thus this is the critical concentration used for the selection of probiotic bacteria. Papamanoli et al. [23] consider as bile salts tolerance when a bacterial population reduces the number of viable cells from 10⁶ - 10⁷ CFU/ mL to 10⁵ CFU/ mL in a 4 hour period.

Erkkilä and Petaja [22] observed a reduction of 1 log cycle in the initial number of viable cells of Lactobacillus curvatus and Pediococcus acidilactici when grown in a medium containing 0.3% bile salts and pH 6 after 4 hours of exposure.

From a total of 63 bacterial strains isolated from fermented sausages, canned fish, bakery dough and jellies, 9 strains of Lactobacillus sp. were able to survive at pH 2.5, while only strains of Lactobacillus casei e Lactobacillus plantarum showed survival at pH 2 and in the presence of bile salt [49].

Macedo et al. [44] found resistance of Lactobacillus paracasei to 0.3% bile salt.

Meat has also been reported to protect microbes against bile [50]. During meat sausage processing, Lactobacillus added to the batter are encapsulated by the matrix consisting of meat and fat. Due to the protection exerted by the food, the survival of Lactobacillus in vivo during transit through the stomach and intestine appears to be higher than that observed by the in vitro exposure of the microorganisms to low pH and bile salts [1, 22].

2.3.3.3. Detoxification capacity of biogenic amines produced in meat products

The biogenic amines, organic bases with aliphatic, aromatic or heterocyclic structures, are produced by the microbial decarboxylation of amino acids present in meat products, either by naturally occurring microorganisms or from the starter culture. The biogenic amines such as histamine, tryptamine, tyramine, cadaverine, putrescine and spermidine can cause toxic effects, especially in consumers with amino oxidase deficiency. In fermented meat products, biogenic amines producing microorganisms have a favorable environment due to the high protein content and the intense proteolytic activity that occurs during the long ripening time of these products. However, some strains of Lactobacillus are able to produce amino acid descarboxylase that prevents the accumulation of biogenic amines in the product. Thus, the selection of probiotic bacteria for use in fermented meat products must also be based on its ability to oxidate biogenic amines formed in the product and to prevent the formation of new amine by the rapid drop of pH that inhibits the growth of amine producing microorganisms. In fermented meat products, amine oxidase activity was detected in strains of Lactobacillus casei and L. plantarum [6, 14].

Ergönül and Kundakçi [51] found low biogenic amine contents in a Turkish fermented sausage manufactured by using three different probiotic starter culture combinations (Lactobacillus casei, L. acidophilus or their combination). Putrescine contents of the samples were ranging between 1.98 and 35.48 ppm during manufacturing and refrigerated storage (8 months), respectively, whereas the values were 0.96–18.50 ppm for cadaverine, 1.41– 10.84 ppm for histamine and 1.75–9.36 ppm for tyramine.

2.4. Beneficial effects associated with the consumption of probiotic meat products

As described earlier, most research involving probiotics in meat products focuses on the survival of probiotic species in the meat matrix and its influence on the technological and sensory characteristics of the final product. Few studies report the effects of consumption of these products on host health [7]. This condition is mainly due to the fact that in vivo tests are expensive, require more time for experimentation and the approval by ethics committees [36].

One of the few studies reporting the effects of the consumption of probiotic meat product on the human health was carried out by Jahreis et al. [52]. These authors evaluated the effect of daily consumption of 50g of probiotic salami containing L. paracasei LTH 2579 on the immunity system and blood triglycerides and cholesterol levels of healthy volunteers for a few week period, and obtained moderately satisfactory results. Although it has been observed effect on immunity of the host, small effect was observed on the plasmatic lipid levels.

In laboratory animals probiotic administration has shown to decrease the blood cholesterol level and increase the feed-conversion rate [53]. L. plantarum administration was reported to increase CD-8 and CD-4 lymphocytes in lab rats [54].

Other important physiological properties to be considered for the potential probiotics are the adhesive capacity toward Caco-2 cells and the antagonism toward pathogenic organisms [3].

Klingberg et al. [21] evaluated the ability of probiotic cultures to colonize the human intestinal tract by in vitro study using Caco-2 cells isolated from human colon adenocarcinoma. The starter strains Pediococcus pentosaceus, Lactobacillus pentosus and L. plantarum showed higher ability to adhere to cells in comparison to Lactobacillus rhamnosus used as control strain in the experiment.

Lactobacillus plantarum isolated from sausages exhibited superior adhesive properties toward Caco-2 cell lines as compared to L. paracasei and L. brevis [55].

The majority of studies on probiotic meat products focuses on the inhibition of pathogens by probiotics, increasing the safety of meat products. Mahoney and Henriksson [56] tested the inhibition of colonization and virulence of Listeria monocytogenes in the intestinal tract of rats by the consumption of fermented meat product with the addition of starter cultures, probiotic cultures and Listeria monocytogenes. The results showed that the starter culture consisting of Pediococcus pentosaceus and Staphylococcus xylosus, and the probiotic culture consisting of Lactobacillus acidophilus, L. paracasei and Bifidobacterium sp. were able to inhibit the growth of Listeria monocytogenes during its passage through the gastrointestinal tract. There was also a possible protective effect of the sausage on the intestinal mucosa by involving the pathogenic bacteria in its matrix and thus, not allowing it to adhere and colonize the intestine.

Autoaggregation of probiotic strains appears necessary for their adhesion to intestinal epithelial cells and coaggregation presents a barrier that prevents colonization by pathogenic microorganisms. Yuksekdag and Aslim [57] reported autoaggregation capacity of five Pediococcus strains isolated from a Turkish-type fermented sausages (sucuk) ranging from 35% to 84%. The high EPS (exopolysaccharide) producing P. pentosaceus Z12P and Z13P strains showed greater autoaggregation (79% and 84%, respectively) than the other strains. The coaggregation scores of those Pediococcus species with L. monocytogenes ATCC 7644 ranged from good (Z12P and Z13P) to partial (Z9P, Z10P, and Z11P).

Growth inhibition of Escherichia coli O157:H7 by the use of Lactobacillus reuteri ATCC 55730 and Bifidobacterium longum ATCC 15708 in the production of salami was confirmed by Muthukumarasamy and Holley [38]. Sameshima et al. [9] found that Lactobacillus rhamnosus FERM P-15120, L. paracasei subsp. paracasei FERM P-15121 and starter culture L. sakei were able to inhibit the growth and the toxin production of Staphylococcus aureus in fermented meat product.

Nedelcheva et al. [58] demonstrated the ability of Lactobacillus plantarum NBIMCC 2415 to inhibit the growth of pathogenic microorganisms such as Escherichia coli ATCC 25922, Escherichia coli ATCC 8739, Proteus vulgaris G, Salmonella sp., Salmonella abony NTCC 6017, Staphylococcus aureus ATCC 25093, Staphylococcus aureus ATCC 6538 P and Listeria monocytogenes at drying temperature (15-18 ^oС) for use in raw-dried meat products.

In addition to the studies related to the improvement of the safety of meat products with the use of probiotics, these bacteria have also been assessed for in situ production of nutraceutical compounds in meat products. Ammor and Mayo [14] describe studies related to high production of folate (vitamin B11) by a genetically modified Lactobacillus plantarum. Likewise, the production of conjugated linoleic acid (CLA), which has anticancer, antiobesity, antidiabetic, and antiatherogenic properties as well as stimulates the immune response, has been reported in some probiotic bacteria. Thus, the property of some probiotic bacteria to produce micronutrients and nutraceuticals compounds may allow in situ fortification of meat products, making them more nutritious and healthy.

The combined effect of the addition of probiotics and other active ingredients such as dietary fiber in meat products has also been studied. Sayas-Barberá et al. [59] reported that the addition of Lactobacillus casei CECT 475 to a traditional Spanish dry-cured sausage (Longaniza de Pascua) accelerates the curing process and that the incorporation of 1% orange fiber promotes the growth and survival of lactobacilli and micrococci, enhancing the microbial quality and safety of the sausages.

3. Conclusion

The fermented sausages fit perfectly in the current consumption trend due to their ease of preparation (ready to eat), ease of conservation, versatility of use (individually or as an garnish in cooking plates), nutritional appeal and variety of forms of presentation [60]. In this regard, probiotic fermented meat products might be the trend setters for development of innovative meat products.

Despite the selling of probiotic meat products occurs since 1998 in countries like Germany and Japan, further human-based studies are needed to establish documented proofs of the beneficial effect of these products, mainly with research on health promotion in humans [7]. Only after these studies will be possible to confirm the intrinsic value of fermented meat products and contribute to the recognition of such products as health foods.