Influence of a native strain of Staphylococcus xylosus on the microbiological, physicochemical and sensorial characteristics on milano salami type

FOOD/FEED SCIENCE AND TECHNOLOGY

Influence of a native strain of Staphylococcus xylosus on the microbiological, physicochemical and sensorial characteristics on milano salami type

Ângela Maria Fiorentini^I,II,*; Maristela Cortez Sawitzki^I; Teresinha Marisa Bertol^III; Anildo Cunha Júnior^III; Ernani Sebastião Sant'Anna^I

^IDepartamento de Ciência e Tecnologia de Alimentos; Centro de Ciências Agrárias; Universidade Federal de Santa Catarina; Rod. Admar Gonzaga, 1346; 880034-001; Florianópolis - SC - Brasil

^IIDepartamento de Biologia e Química; Universidade Regional UNIJUÍ; RS 344, km 39; 98900-000; Santa Rosa - RS - Brasil

^IIIEmbrapa Suínos e Aves; BR 153; km 110; 89700-000; Concórdia - SC - Brasil

ABSTRACT

In this work, the influence of native starter cultures on the microbiological, physicochemical and sensorial characteristics of Milano salami type was studied. Two batches of Milano salami type were produced: Batch A, with the addition of Staphylococcus xylosus U5 and Batch B (control) without the starter culture. The Milano salami type was characterized by an important microbial activity of coagulase-negative staphylococci (CNS) that resulted in substantial growth in Batch A during the ripening with an initial count of 7.60 log cfu.g^-1 and reached 9.84 log CFU.g^-1 after 14 days. Bacterial enzymes that showed efficient activity under the conditions found in Milano salami type were catalase, nitrite and nitrate reductase, contributing for sensory and physicochemical properties of the product. There were no significant differences in general free fatty acids composition among the batches, while the color parameters (L *, a * and b *) in the Batch A presented significantly higher values in relation to Batch B. Moreover, batch A had the higher preference in sensorial analysis.

Key words:Staphylococcus xylosus, starter cultures, milano salami type

RESUMO

A análise da influência de culturas iniciadoras nativas nas características microbiológicas, físicoquímicas e sensoriais de salame tipo Milano foi o objeto deste estudo. Foram produzidos dois grupos de salame tipo Milano: Grupo A - com aplicação de linhagem Staphylococcus xylosus U5 enquanto o controle, Grupo B, foi produzido sem culturas iniciadoras. O salame tipo Milano foi caracterizado pela importante atividade microbiana de estafilococos coagulase negativo (SCN), que resultou significativo crescimento no Grupo A durante a maturação, com contagem inicial de 7,60 ufc.g^-1 e alcançando um crescimento de 9,84 cfu.g^-1 depois de 14 dias. As enzimas bacterianas que mostraram eficiente atividade sob as condições encontradas no salame tipo Milano foram catalase, nitrito e nitrato redutase, contribuindo para as propriedades físicoquímicas e sensoriais do produto. Não houve diferenças significativas na composição geral dos ácidos graxos livres entre as amostras, enquanto os parâmetros de cor (L*, a* e b*) obtidos no salame inoculado (Grupo A) diferiram significativamente em relação ao controle (Grupo B) e foi o grupo preferido pelos degustadores.

INTRODUCTION

Fermented sausages can be defined as the meat products consisting of a mixture of meat and fat particles, salt, curing agents, spices, etc., which acquire their characteristic properties through a process involving the microorganisms (Hammes, 1990). Spontaneous fermentation has been applied for thousands of years mainly as a method for the preservation of foodstuffs and as a way to obtain the spicy and flavorful foods (Drosinos et al., 2007). Generally, lactic acid bacteria (LAB) and Micrococcaceae are the main groups involved in Fermented sausages can be defined as the meat the fermentation of dry cured sausages (Lücke and products consisting of a mixture of meat and fat Hechelmann, 1987; Coventry and Hickey, 1991). particles, salt, curing agents, spices, etc., which The manufacturing of fermented sausage has a acquire their characteristic properties through a long history in Brazil. As influence of Italian process involving the microorganisms (Hammes, immigration in the beginning of the 20^th century, it 1990). Spontaneous fermentation has been applied is still regarded as the Italian traditions. Even for thousands of years mainly as a method for the when the use of starter culture has become preservation of foodstuffs and as a way to obtain common in the products, many typical artisanal the spicy and flavorful foods (Drosinos et al., sausages are still produced with the traditional technologies without selected starters.

A wide variety of microorganisms have already been isolated by traditional methods, from spontaneous fermentations, mainly represented by the coagulase-negative staphylococci (CNS), such as Staphylococcus xylosus, S. saprophyticus and S. carnosus (Coppola et al., 1997; Garcia-Varona et al., 2000; Papamanoli et al., 2002; Mauriello et al., 2004; Drosinos et al., 2005). Several strains have been isolated and characterized in terms of their technological properties, mainly proteolysis (Fadda et al., 1998; Bover-Cid et al., 1999), lipolysis (Molly et al., 1996; Mauriello et al. 2004), production of antimicrobial compounds (Aymerich et al., 2000; Messens et al., 2003, Drosinos et al., 2007), decarboxylation of specific amino acids (Martuscelli et al. 2000; Bover-Cid et al., 2001) and others (Mauriello et al., 2004).

Coagulase-negative staphylococci (CNS) are important microorganisms in meat products. They have several technological advantages, such as nitrite and nitrate reductase activity, oxygen consumption and catalase activity that improve the colour stability and decrease rancidity development in the product (Geisen, Lücke, and Kröckel, 1992). Berdagué et al., (1993) established a correlation between the type of starter culture and flavour of fermented sausages. Montel et al., (1996) proved that staphylococci contributed to the generation of typical fermented sausage flavor, possibly due to proteolytic and lipolytic capability (Rodríguez et al., 1998; Berdagué et al., 1993).

S. xylosus is one of the main staphylococci species found in most naturally fermented sausages (Montel et al. 1992; Coppola et al. 1997; Rebecchi et al. 1998; Cocolin et al., 2001). Fiorentini et al., (2009) reported its presence in artisanal sausages in South region of Brazil. Due to these properties, S. xylosus is considered as a suitable starter culture in sausage production. In selecting a suitable starter strain, it should be taken into account that the strain must compete with the same species, or with closely-related species, occurring in a single environment, the so-called 'house flora' (Santos et al., 1998). In production of traditional fermented sausages it is important to use selected starter cultures due to a low variability of present microflora. Selected starter cultures consist of isolated strains from local products being well adapted to the particular product and to the specific production technology (Papa and Grazia, 1990). Besides, they could dominate the microflora of fermented meat product (Papamanoli et al., 2003). The Brazilian legislation allows the use of starter cultures and considers them as technological coadjutants (BRASIL, 2000).

A strain of S. xylosus U5 was isolated and identified by Fiorentini et al., (2009). This strain was isolated from the indigenous flora of naturally fermented sausages and recommended, due to technological potential, for using as starter cultures in fermented sausage. Therefore, the aim of the present work was to investigate the influence of native starter cultures -Staphylococcus xylosus U5 - on microbiological, physicochemical and sensorial characteristics in Milano salami type.

MATERIALS AND METHODS

Microorganism

Staphylococcus xylosus strain U5 is part of a group of microorganisms isolated from artisanal sausages collected in twenty-one cities of South Region of Brazil. The strain S. xylosus U5 was selected as a starter culture on the basis of its catalase positive activity, capacity to reduce nitrate and nitrites, lipolytic activity and no enterotoxin production in broth. It was also subjected to phenotypic and molecular characterization (Fiorentini, et al., 2009).

Starter preparation

Freeze-dried cultures of S. xylosus U5 were resuspended in sterile distilled water in the absence of chlorine and then added to the meat mixture in concentration of 9 log cfu per gram of raw material.

Milano salami type preparation

Milano salami was manufactured in local industry plants using traditional techniques, selected raw materials and good manufacturing practices. Sausages had the following composition (%): pork (53.5), beef (17.8), pork back fat (17.8), NaCl (2.8), sodium nitrate and sodium nitrite (0.45), maltodextrins (0.5), sodium eritorbate (0.25), glucose (0.5), sucrose (0.5), skimmed milk powder (3.0), red wine and mixed spices. Sausages were prepared by grinding meat and pork back fat, and then adding the ingredients. After mixing, two batches were prepared: Batch A with the addition of S. xylosus U5 freeze-dried culture (9 log cfu.g^-1 of raw material) and Batch B was used as the control (not inoculated), without selected starters. Batches were then stuffed into collagen casings (70 mm diameter). Afterwards, sausages with about 800 g each were transferred into a drying chamber and then kept under the following parameters of relative moisture and temperature during ripening, respectively: 25 ºC and 95 % (1st day), 24ºC /93 % (2nd day), 23ºC / 90 % (3rd day), 22ºC / 85 % (4th day), 21ºC / 80 % (5th day), 20ºC / 75 % (6th day) and 18ºC /75 % (7th day). These conditions were maintained for 42 days, the end of ripening.

Sampling procedure

Experiments were carried out for 42 days. Samples were randomly taken from each batch at 1, 7, 14, 21, 28 and 42 days for analyses.

Microbiological analyses

Microbiological analyses were carried out in order to monitor the dynamic changes during the storage of the sausages and their sanitary quality. In particular, 25 g of each sample were transferred into a sterile stomacher bag and 225 ml of sterile 0.1% peptone water (Oxoid) were added and mixed for 1 min in a Stomacher machine (ITR, mod.MK 1204). Serial decimal dilutions in 0.1% peptone water were prepared and 1 mL or 0.1 mL samples of appropriate dilutions were poured or spread in duplicate. Analyses were carried out according to APHA (1992): (a) aerobic mesophilic counts were determined on plate count agar (PCA, Oxoid), incubated at 30ºC for 48-72 h; (b) LAB on MRS agar (Oxoid) incubated at 30ºC for 72 h under anaerobic conditions; (c) coagulase-negative staphylococci (CNS) on BHI Agar (Oxoid) incubated at 35ºC for 48 h; (d) total coliforms on Brilliant Green Bile (2%) Broth (Oxoid) after 48 h at 37ºC ( MPN method); (e) thermotolerant coliforms on EC broth (Oxoid) incubated at 42ºC for 24 h (MPN method); (f) Staphylococcus aureus on Baird-Parker medium (Oxoid) with egg yolk tellurite emulsion (Oxoid) incubated at 37ºC for 24- 48 h; (g) yeasts and molds on glucose potato agar (Oxoid), supplemented with tetracycline (1 mg/mL, Sigma), incubated at 25ºC for 5-7 days; (h) sulfite-reducing clostridia on agar and incubated anaerobically at 37ºC for 48 h. (i) for the detection of Salmonella, pre-enrichment was done by suspending 25 g of sample in 225 ml buffered peptone water (Merck), followed by incubation at 37ºC for 16-20 h. Selective enrichment was done by transferring 0.1 mL of pre-enrichment culture in 10 mL Rappaport-Vassiliadis broth (RVS broth, Merck), followed by incubation at 42ºC for 24 h.

After incubation, samples were streaked on the modified BPLS agar, (Merck) (37ºC for 24 h) and XLD agar (Merck) (37ºC for 48 h); (j) for the detection of Listeria, enrichment was done by suspending 25 g of sample in 225 mL Fraser broth (Merck), followed by incubation at 30ºC for 24 h. Then, 0.1 mL of the culture enrichment were streaked on PALCAM agar (Merck) and incubated at 30ºC for 48 h. Tests were carried out in duplicate on two sausages and the results were expressed as log10 cfu.g^-1 or MPN.g^-1 .

Physicochemical analysis

Samples were ground and blended in a grinder (Tecnal Turratec TE-102) and freeze-dried (Virtis Unitop/1000L). For monitoring the dynamic chemical changes, during and at the end of the fermentation/ripening process, the following analyses were performed (every 7 days): moisture (oven air-drying method), ash (muffle furnace), proteins (Kjeldhal nitrogen), fat (etheric extract), peroxide values, nitrite and nitrate content, acid value (% lactic acid) were performed according to AOAC (2002). Iron and sodium analyses were carried out according to Granadillo et al. (1995). Approximately 500 mg of samples were weighed into a digestion vessel (22 x 250 mm), added 6.0 mL of HNO3:HClO4 8:1 (v/v) and heated as follows: 90 ºC.30 min^-1, rampered to 160 ºC.40 min^-1 (10 ºC. min^-1), 180 ºC.20 min^-1 and held this temperature until disappearing white steam. After digestion, 2.5 mL of HCl (6M) were added and volume adjusted to 25 mL. Iron (Fe) was determined by flame atomic spectrometric analysis. For this, the diluted samples were directly aspirated into a spectrometer (Varian SpectrAA 220) equipped with lamp of hollow cathode, using air/acetylene flame. Sodium (Na) was determined by flame photometry (Micronal B262). Both, Fe and Na, were quantified according to operating parameters provided by the respective equipment's manufacturer. Two independent measurements were made on each sample. Means and standard deviations were calculated.

Free fatty acids (FFA) determination

Samples were freeze-dried (Virtis Unitop/1000L) and lipids were extracted according to Folch et al, (1957). From this extract, an aliquot of 10 mL was taken and the total lipid content was determined gravimetrically. A further aliquot, containing approximately 100 mg of lipid was esterified, and the fatty acid composition was determined by the gas chromatography (GC) (Shimadzu 2010). Dried lipid extract was esterified with a solution of ammonium chloride and sulfuric acid in methanol (Hartman and Lago, 1973). Fatty acid methyl esters were separated on a GC (Shimadzu 2010) system coupled to mass selective detector (Shimadzu QP2010). Separation was performed on a MS-5 capillary column (30 m;·0.25 mm I.D. x 0.25 µm film thickness) (Restec Rtx®). Carrier gas was helium with a linear flow rate of 1.0 mL min^-1. Temperature program was 150 to 220ºC at 2ºC min^-1 and held for 15 min. Samples of 1 µl were injected in split less mode (100:1) and the injector temperature was set at 250ºC. Mass spectra were obtained under following conditions: 70 eV in the 40-4000 u range. Ion source was held at 220ºC and quadrupole at 250ºC.

Fatty acids were identified by comparing the mass spectral data of sample components with those of known compounds from library databases (NIST05). Authentic standards of several detected compounds were analyzed in order to confirm the reliability of retention times and tentative identities, considering a similarity higher than 90%. Results were expressed in % of normalized area. Quantification was carried out by normalization and conversion of area percentage into g.100 g^-1 of edible portion, using the lipid conversion factor (F). An F-value of 0.956 was used for processed meat products based on Holland et al. (1994). Two independent measurements were made on each sample. Means and standard deviations were calculated.

Colour evaluation

Colour evaluation was determined in Batch A and B of Milano salami type at the end of the maturation period, using a reflectance colorimeter (Chroma Meter CR-300, Minolta). CIE L^* (lightness), a^* (redness), b^* (yellowness) colour values were measured. Colour readings were taken at three points of the cut surface of the two slices (10mm). Six measurements were taken for each sample.

Enterotoxin detection

Enterotoxins were detected using the automated VIDAS instrument (bioMérieux) and a VIDAS® Staph enterotoxin SET 2 kit (bioMérieux). Extraction of enterotoxins (Batch A and B) was performed as described in the protocol for meat products according to manufacturer's instructions (SET 2 kit). Relative fluorescence value (RFV) obtained was interpreted by VIDAS system as follows: negative when TV (Test Value) < 0.13 and positive when TV > 0.13.

Sensorial analysis

Sensorial analyses were carried out at the end of the ripening by a panel of 70 untrained panelists consisted of students and professors of Department of Science and Technology of Food. In order to evaluate the acceptance of sausages, tasters were asked to ordinate the samples from lower to higher preference (ABNT/NBR12994/1993 and NBR13170/1994). All the participants signed TCLE -Term of Free and Illustrious Consent, in accordance with the Project 189/05: Development of starter cultures for the production of artisanal sausages approved on June 27, 2005 for the Committee of Ethics in Research with Human beings of the Federal University of Santa Catarina, Brazil.

Statistical analysis

Data of physicochemical analyses are reported as mean values ± standard deviation. To verify the differences among the sausages, results were submitted to the t-Test at 5% level of confidence (STATISTICA 6.0).

RESULTS AND DISCUSSION

Results of microbiological analysis of the Milano salami type during the fermentation and ripening are presented in Figure 1. Initially, the counts of aerobic mesophilics were slightly lower in Batch B than in Batch A. After 14 days counts, the Batches A and B were significantly different (P<0.05), reaching 8.62 and 6.49 log CFU.g^-1, respectively. Gram-positive, catalase-positive cocci - Coagulase-negative staphylococci (CNS) counts in the inoculated sample (Batch A) showed a substantial growth (P<0.05) of this group during the ripening. In Batch A, initial count was of 7.60 log CFU.g^-1, reaching 9.84 log CFU.g^-1 after 14 days. In control (Batch B), these microorganisms were found at very lower concentrations and after 14 days their number reached 6.95 log CFU.g^-1 (Fig.1). This substantial growth (2 log) was due to lower concentrations of lactic acid bacteria (LAB) during the fermentation and ripening that reached at maximum levels of about 6.34 log CFU.g^-1 (Fig. 1c). However, sensibility of Micrococcaceae in the presence of high acidification was not affected (Palumbo and Smith, 1977); Lücke, 1985). In agreement with works of Comi et al., (1992) and Samelis et al., (1993), Micrococcaceae might become more competitive and reach 1-2 log higher counts in the case of a final pH above 5.5 in fermented sausages manufactured in artisanal scale. As LAB were not used as starter culture in the present work, their counts were not different between the control and inoculated batch. In fact, several species of LAB are part of the meat microflora.

The level of total and thermotolerant coliforms (<3 NMP) was similar in both the batches, but in the inoculated samples (Batch A), their number presented a sharp decrease. After 7 days of ripening, no viable cells of total and thermotolerant coliforms were detected. In control (Batch B), total coliforms were present even after 7 days and only after 21 days of ripening, their number decreased to undetectable levels. These results indicated that the strains of CNS were competitive and able to produce the antagonistic substances against the pathogenic bacteria, because in that period the counts of CNS in inoculated salami was around 8 log cfu.g^-1 . According to Pinto et al. (1998) and Essid et al. (2007) many strains of S. xylosus had antimicrobial activities against undesirable strains.

Papamanoli et al. (2003) found that the once strains isolated from traditional sausages were well-adapted to sausages conditions, they were competitive. Nevertheless, both the coliforms were absent in the final product. Moulds and yeasts did not seem to play any significant role in sausages. Maximum counts of about 2.77 log cfu.g^-1 were observed for them and were not detected in the most cases. These results met the requirement of the Brazilian legislation - sanitary microbiology patterns for ripening the meat product (BRASIL/ANVISA, 2001) - and confirmed the need of good manufacturing practices in order to obtain the reduced contamination of undesirable microorganisms.

Both the batches were free of Salmonella and Listeria after formulation, as well as the low number of sulfite-reducing clostridia (< 1) and coagulase positive staphylococci (< 2). These results also met the requirement of the legislation for fermented meat products during fermentation and in the final product. According to Drosinos et al. (2005), these results indicated the importance of selecting the raw materials of good microbiological quality for dry sausage manufacture.

Results of the physicochemical analyses of Milano salami type during fermentation and ripening are presented in Table 1. During the ripening, pH showed low variation among the batches (A and B), probably due to low presence of LAB, which were responsible for pH decrease and that the changes in pH due to Staphylococci were not significant. According to Olesen et al. (2004), Staphylococcus strains produce limited quantities of acid. The pH measured at the beginning of fermentation in both the batches was around 5.6 and decreased to around 5.2 after 7 days of ripening. A slight increase in pH was observed in the final product, with values around 5.3 in both the batches. These results were in agreement with those found for Galgano et al., (2003). This could be due to the production of ammonia and other basic compounds, such as peptides, amino acids, aldehydes, amines and free fatty acids arising from the proteolytic activity (Mauriello et al., 2004).

Water activity (aw) and moisture presented a constant decrease during the maturation (Table 1), while protein, fat, ash, NaCl, Na and Fe content increased during the ripening because of the effect of dehydration. These results were in agreement with Brazilian legislation (BRASIL, 2000). The low amount of lactic acid (%) (Table 1) was probably due to the activity of CNS that produced very limited amounts of acid or, yet, to the low presence of LAB.

Nitrate and nitrite are known as meat preservatives. Nitrate does not present antioxidant activity but becomes functional in nitrite reduction (Terra et al., 2004). During the fermentation and ripening nitrate is reduced to nitrite, which is the major active ingredient in salt mixtures (Cammack, 1999). Nitrate and nitrite levels decreased during the fermentation and ripening and concentrations were statistically different (P > 0.05) among the batches A and B (Fig. 2), probably due to the Micrococcaceae. Several studies have demonstrated that S. xylosus is able to reduce the nitrate by the secretion of a nitratoreductase (Montel et al., 1996; Talon et al., 1999; Mauriello et al., 2004; Fiorentini et al., 2009).

Nitrite concentrations needed for colour development range from 30 to 50 ppm, 20 to 40 ppm for aroma development, 80 to 150 ppm for the conservative effect (Müller, 1991) and 20 to 50 ppm for the antioxidant effect, depending on the type of meat product (Lücke, 2000). In fermented products, nitrite is reduced to nitric oxide through the action of nitrite reductase, also present in the strains of the family Micrococcaceae. This reaction is faster in pH above 5.6 and slower in pH higher than 6.2 (Arnau et al., 1998). For the nitrite reductase enzyme to act as reducer agent, the counts of Micrococcaceae should be close to 6 log CFU.g^-1 (Campbell-Platt and Cook, 1995). During the fermentation and ripening, the decrease in nitrite concentration in both batches could be due to the action of a nitrite-reductase enzyme secreted by the Micrococcaceae, being more pronounced in batch A (7 to 28 days) (Fig. 2), where the Grampositive cocci counts were higher than 6 log.UFC.g-1. In batch B, the decrease of nitrite concentration appeared only after the 14th day (Fig. 1). Nitrite reduction capacity is another characteristic of Micrococcaceae demonstrated by the absence of nitrosamines in fermented meat products (Pinto et al., 2001).

The peroxide value was also determined in this work. During the ripening, low peroxide values were observed in batch A when comparing to batch B, which were significantly different (P<0.05), demonstrating the catalase activity of S. xylosus U5. Lipid oxidation leads to the formation of peroxides which are reduced in the presence of microorganisms with high catalase activity (Varnan and Sutherland, 1995). Catalase activity is important due to its capacity of reducing hydrogen peroxide, which can be formed as a metabolite by LABs and other bacterial species in sausages.

According to Cornforth (1996), nitrite has also an effect in inhibiting the development of rancidity. Traditional meat products, such as dry fermented sausages are interesting models for investigations, once they are exposed to pro-oxidant conditions. Peroxide values were around 2-4 mequivO2.kg^-1 , acceptable levels for a good quality (Fernández and Rodríguez, 1991; Johansson et al., 1994; Ghiretti et al., 1997; Novelli et al., 1998; Zanardi et al., 1998).

The free fat acids found were C14:0; C16:0; C16:1 (9); C17:0; C18:0; C18:1 (9); C18:1 (11); C18:2 (9, 12), (Table 2). In both the batches, a progressive increasing was observed in free fatty acid production during the ripening, but no significant differences (P > 0.05) were noticed among the batches. Even considering that Staphylococcus strains played an important role in lipolysis (Samelis et al., 1993), the values indicated that the S. xylosus strain U5 did not act significantly in the chemical transformations of lipids. Similar results were reported by Montel et al., (1993) where the batch inoculated with Staphylococcus presented fatty acid content similar to control (without addition of starter cultures). In this case, lipolytic processes were not attributed to the Staphylococcus strain. Molly et al., (1997), studying lipolysis, showed that the bacterial activity in sausages was low, once environmental conditions did not offer favorable conditions for bacterial lipases. Stahnke (1994), on the other hand, reported that more than 60% of free fatty acids were released in the sausages with the addition of S. xylosus strains. This indicated that S. xylosus strains were lipolytic as reported in several studies (Comi et al., 1992; Sorensen et al., 1993). Although several bacteria selected due to their lipolytic activity are used as commercial starter cultures, the addition of lipases frequently do not affect the sensorial evaluation of the fermented sausages (Fernández et al., 1991). Besides, bacterial lipolytic activity is influenced by several factors, such as the physiological state of culture, substrate type, pH, temperature, etc. (Talon et al., 1992). Although S. xylosus U5 strain had presented lipolytic activity (Fiorentini et al., 2009), low activity was observed under the conditions found in Milano salami type. Galgano et al., (2003) and Zuber et al., (2007) did not observe any significant change on fatty acids content when evaluating the influence of several strains of S. xylosus in sausage.

Relative percentages of free fatty acids (FFA) after 40 days of ripening are presented in Figure 3. When comparing with control (Batch B), the addition of starter cultures (Batch A) did not cause significant modifications in relative percentages of FFAs. In both the batches, monounsaturated fatty acids were predominant, with a content of 46.99 % in batch A and 45.08% in batch B, and oleic acid (C18:1) was found in highest concentrations (9.37%), followed by palmitoleic acid (C16:1) (7.81%). Polyunsaturated fatty acids were found in low concentrations. Free unsaturated fatty acids are important precursors of flavour in fermented ripened meat products (Molly et al., 1997; Chizzolini et al., 1998). The contents of saturated fatty acids (SFF) were 37.38 and 39.92% for batch A and B, respectively, with palmitic acid (C16:0) and stearic acid (C18:0) representing the highest contents. A reduced content of SFF is desirable in the foods, as they influence the level of blood cholesterol. Similar results were reported for Milano salami (Zanardi et al., 2002; Campos et al., 2006) and for other types of fermented sausages similar to Milano type in ripening time (Domínguez-Fernández e Zumalacárregui, 1991; Hierro et al., 1997; Galgano et al., 2003; Zuber et al., 2007).

Regarding the colour parameters obtained for the Milano salami, significant differences (P < 0.05) were observed between the batches A and B. Batch A showed significantly higher L*, a* e b* values in relation to control (Batch B), probably due to enzymatic action of the added strain of S. xylosus U5 (Table 2). This enzymatic action concerns to nitrate-reductase activity that leads to the formation of nitrosomyoglobin (Talon et al., 1999). Dellaglio et al. (1996), studying an Italian dry-cured sausage (Felino salami), found similar L* values (39.10±47.27) and higher a* values (22.13±30.08), but lower b* values (5.68±8.90). Pagan-Moreno et al. (1992), in chorizo, found lower values for L* (34.72±41.53) and a* (13.87± 17.55), being b* values more similar to that found in the present work (9.33±14.10). In meat and meat products, lightness (L*) seems to be the most informative parameter for color changes (Mielnik and Slinde, 1983) but the importance of red (a*) should not be ignored (Ferreira, Fernandes and Yotsuyanagi, 1994). Chouliara et al., (2006) studied the different factors of action in sausage color: irradiation effect at the end of ripening period of Greek dry fermented sausage (28 days), ands found that the irradiation had little or no effect at the end of ripening on pH, moisture content and color (parameters L*, a*, and b*).

In the present work, staphylococcal enterotoxins were not found in Milano salami type in both the batches (A and B), rejecting the possibility of enterotoxin production by the inoculated strain S. xylosus U5 or by any CNS present in the product, confirming it as a safe product for consumption. Staphylococcal food poisoning occurs by ingestion of the pre-formed enterotoxins in consequence of human manipulation or raw material derived from the contaminated animals. Cunha et al., (2006) evaluated 88 food samples and 4 CNS isolates by PCR and found them positives for the genes that codified the enterotoxins but none enterotoxin production was detected by RPLA method. Very little, however, is known about the growth of CNS in food. Pereira and Pereira (2006), in agreement with results found in the present work, reported that none out of 266 CNS isolates produced enterotoxins and 90 % of the 252 identified CNS isolates were S. xylosus and S.carnosus.

The sensorial evaluation indicated the preference for the inoculated sausage (72.5 %). S. xylosus U5 strain had an enzymatic profile capable of producing desirable sensorial properties in the meat products increasing the product acceptability. Hence, the sensorial quality of the final product is affected by the type of starter culture used in formulation (Berdagué et al., 1993). Micrococcaceae are the main species that contribute in the formation of colour and flavor in the meat products (Montel et al., 1996; Stahnke et al., 2002). These two characteristics are very important for the acceptability of sausages.

S. xylosus strain U5 presented a good development during the fermentations and ripening of Milano salami type. Bacterial enzymes that showed efficient activity under the conditions found in the sausage were catalase, nitrate and nitrite reductase, contributing for the sensorial and physicochemical properties of the product. Colour parameters were higher in the inoculated salami being preferred by the tasters in the sensorial analysis, but no significant differences were observed in general fatty acid composition. S. xylosus strain U5 could be used as a single starter culture in fermented sausages or mixed with LAB as the results obtained for synergism suggested. However, additional studies would be needed in order to evaluate the technological properties of wild strains of S. xylosus in fermented sausages.

ACKNOWLEDGEMENTS

This work was supported by EMBRAPA, Brazil.

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Received: March 10, 2008; Revised: September 24, 2008; Accepted: December 08, 2009.

Publication Dates

• Publication in this collection
  06 Aug 2010
• Date of issue
  Aug 2010

History

• Accepted
  08 Dec 2009
• Reviewed
  24 Sept 2008
• Received
  10 Mar 2008