Correlation between IRC7 gene expression and 4-mercapto-4-methylpentan-2-one production in Saccharomyces cerevisiae strains.

Volatile thiols are not present in must but are synthesized and released by wine yeasts during alcoholic fermentation. In this study, autochthonous and commercial Saccharomyces cerevisiae strains were characterized for the expression of the main genes involved in thiols metabolism and their production in wine. New primer sets were developed on the basis of the S288c genome to evaluate the expression of Cys3, Cys4, MET17 and IRC7 genes. Obtained data revealed the occurrence of some thiols, for example, 4-mercapto-4-methylpentan-2-one (4-MMP) and 3-mercaptohexan-1-ol (3-MH) in Pecorino white wine. All genes were upregulated, but only for IRC7 was found a correlation with 4-MMP release: strains with the highest production showed the highest transcription level. IRC7 gene could be proposed as target for the selection of S. cerevisiae strains to increase thiols content in wine.

Development of a rapid method for the detection of Yersinia enterocolitica serotype O:8 from food.

In this study, a new and alternative method based on monoclonal antibodies (MAbs) for the rapid detection of Yersinia enterocolitica O:8 was developed. This microorganism is an emerging foodborne pathogen causing gastrointestinal disease in humans. The transmission can occur through contaminated food such as raw or undercooked meat, milk and dairy products, water and fresh vegetables. Nine MAbs (46F7, 54B11, 54C11, 62D10, 64C7, 64C10, 72E8, 72E10, 72G6) were characterized and selected versus Y. enterocolitica O:8, and only 2 of them showed also a weak cross-reaction with Campylobacter jejuni. The MAb 54B11 was used for the development of Y. enterocolitica capture-ELISA in food matrices, i.e. meat and dairy products (n = 132). The method was validated by ISO 16140:2003 and compared with the official method for the detection of presumptive pathogenic Y. enterocolitica (ISO 10273:2003). Relative accuracy, sensitivity and specificity corresponded to 100%. The selectivity was evaluated on other food samples (n = 126) showing a lower confidence limit of 90.3% and an upper confidence limit of 100%. The results from this study demonstrated that the developed method was rapid and cheap, specific and sensitive for the screening of the pathogen in food.

Histamine Food Poisoning.

The consumption of food containing high amounts of histamine and other biogenic amines can cause food poisoning with different symptoms linked to the individual sensitivity and the detoxification activity. Histamine is the only biogenic amine with regulatory limits set by the European Commission in fish and fishery products, because it can lead to a fatal outcome. However, also fermented foods can be involved in outbreaks and sporadic cases of intoxication. The factors affecting the presence of histamine in food are variable and product specific including the availability of the precursor amino acid, the presence of microorganisms producing decarboxylases, and the conditions allowing their growth and enzyme production. Generally, the good quality of raw material and hygienic practices during food processing as well as the use of histidine decarboxylase-negative starter cultures can minimize the occurrence of histamine. Further studies are necessary to estimate the human exposure and the relationship between the total amount of the biogenic amines ingested with food and health effects.

Biodiversity of autolytic ability in flocculent Saccharomyces cerevisiae strains suitable for traditional sparkling wine fermentation.

Yeasts involved in secondary fermentation of traditional sparkling wines should show specific characteristics, such as flocculation capacity and autolysis. Recently it has been postulated that autophagy may contribute to the outcome of autolysis. In this study, 28 flocculent wine Saccahromyces cerevisiae strains characterized by different flocculation degrees were studied for their autolytic and autophagic activities. Autolysis was monitored in synthetic medium through the determination of amino acid nitrogen and total proteins released. At the same time, novel primer sets were developed to determine the expression of the genes ATG1, ATG17 and ATG29. Twelve strains were selected on the basis of their autolytic rate and ATG gene expressions in synthetic medium and were inoculated in a base wine. After 30, 60 and 180 days the autolytic process and ATG gene expressions were evaluated. The obtained data showed that autolysis and ATG gene expressions differed among strains and were independent of the degree of flocculation. This biodiversity could be exploited to select new starter stains to improve sparkling wine production. Copyright © 2016 John Wiley & Sons, Ltd.

Influence of pig rennet on fatty acid composition, volatile molecule profile, texture and sensory properties of Pecorino di Farindola cheese.

BACKGROUND: Pig rennet is traditionally used in Pecorino di Farindola cheese. In this study, different Pecorino cheeses obtained using calf, kid and pig rennets were compared in terms of fatty acids, volatile molecule profile, texture and sensory properties during ripening. RESULTS: The rennet type influenced the fatty acid composition of cheeses, though palmitic, myristic and oleic acids were always predominant. The analysis of volatiles by SPME-GC/MS showed that Pecorino from calf rennet, at the end of ripening, was the least 'evolved' in terms of volatile profile. SPME-GC/MS analysis revealed that cheeses from calf rennet showed the slowest accumulation of free fatty acids over ripening time. Volatile data permitted the differentiation of cheese samples ripened from 30 to 180 days according to the rennet used. Texture analysis differentiated cheeses made with pig and calf rennet from those made with kid rennet, which were less hard and more elastic than the former. Also sensory analysis differentiated cheese samples on the basis of rennet type, and cheeses made with pig rennet showed the lowest elasticity, bitter taste and fruity and hay flavour intensities. CONCLUSION: Pig rennet is fundamental to determine the quality parameters of Pecorino di Farindola cheese and could be used to impart peculiar quality features to ewe's milk cheeses.

Biodiversity study of wine yeasts belonging to the "terroir" of Montepulciano d'Abruzzo "Colline Teramane" revealed Saccharomyces cerevisiae strains exhibiting atypical and unique 5.8S-ITS restriction patterns.

The Montepulciano d'Abruzzo "Colline Teramane" premium wine DOCG is produced in the Teramo province (Abruzzo, Italy). This region has a great tradition in winemaking and the wine is produced by a spontaneous fermentation so it could represent a reservoir of wine natural yeasts with important oenological features. The aim of this study was to characterize the yeast community of this wine grape growing region in order to create a Saccharomyces cerevisiae bank, providing data on oenological properties for potential industrial applications. A total of 430 yeasts were isolated at the end of spontaneous fermentation. PCR-RFLP was applied for the identification at the species level and underlined that 14 strains exhibited unusual and characteristic restriction patterns different from those typical of the species S. cerevisiae. This difference was due to the insertion of base C at a position 138 in the ITS1 region that determined an additional cleavage site for the enzyme HaeIII. This insertion could be associated to the fermentative performance and associated to the relationship existing between yeasts and a viticulture region or 'terroir'.

Impact of microbial cultures on proteolysis and release of bioactive peptides in fermented milk.

This study aimed at evaluating co-cultures of selected microorganisms for their proteolytic activity and capability to produce fermented milk enriched with ACE-inhibitory (ACEI) peptides. Selected yeasts (Torulaspora delbruekii KL66A, Galactomyces geotrichum KL20B, Pichia kudriavzevii KL84A and Kluyveromyces marxianus KL26A) and lactic acid bacteria strains (Lactobacillus plantarum LAT03, Lb. plantarum KLAT01 and the not virulent Enterococcus faecalis KE06) were screened as single cultures for their capacity of releasing ACEI peptides without producing bitter taste. Three strains cultures (yeast, Lb. plantarum and E. faecalis) were performed to evaluate the combined impact on microbial growth, lactic acid production, citric acid consumption, proteolysis, ACEI activity, and bitter taste after 36 h of fermentation at 28 °C. While G. geotrichum KL20B showed a strong stimulating effect on Lb. plantarum strains and the production of peptides with ACEI activity, the presence of T. delbruekii KL26A in the cultures was deleterious both to ACEI activity and product taste. The most effective combination was P. kudriavzevii KL84A, Lb. plantarum LAT3, E. faecalis KL06, which showed the highest ACEI activity (IC50 = 30.63 ± 1.11 µg ml(-1)) and gave no bitter taste for 7 days at 6 °C. Our results highlight the importance of choosing the strains combination carefully, to obtain a high yield of ACEI activity without bitter taste.

High content of biogenic amines in Pecorino cheeses.

Pecorino refers to Italian cheeses made exclusively from raw or pasteurized ewes' milk, characterized by a high content of fat matter and it is mainly produced in the Middle and South of Italy by traditional procedures. The autochthonous microbiota plays an important role in the organoleptic traits of Pecorino cheese and it can influence biogenic amines (BA) content. The aim of this study was to characterize from microbiological and chemical point of view 12 randomly purchased commercial cheeses produced in Abruzzo region. Moreover, the BA content and the bacteria showing a decarboxylating activity were detected. For this purpose, a real-time quantitative PCR (qPCR) was applied to evaluate histamine and tyramine-producers. The samples were well differentiated for microbial groups composition, such as aerobic mesophilic bacteria, Enterobacteriaceae, coagulase-negative staphylococci, yeasts, enterococci, mesophilic and thermophilic lactobacilli. Pathogens such as Salmonella spp., Listeria monocytogenes and Escherichia coli O157:H7 were absent in all samples. In most samples the content of BA resulted to be high, with prevalence of histamine and tyramine. In particular, total BA content reached 5861 mg/kg in Pecorino di Fossa cheese. The qPCR method resulted to be very useful to understand the role of autochthonous Pecorino cheese microbiota on BA accumulation in many different products. In fact, since the ability of microorganisms to decarboxylate aminoacids is highly variable being in most cases strain-specific, the detection of bacteria possessing this activity is important to estimate the risk of BA cheese content.

Candida zemplinina can reduce acetic acid produced by Saccharomyces cerevisiae in sweet wine fermentations.

In this study we investigated the possibility of using Candida zemplinina, as a partner of Saccharomyces cerevisiae, in mixed fermentations of must with a high sugar content, in order to reduce its acetic acid production. Thirty-five C. zemplinina strains, which were isolated from different geographic regions, were molecularly characterized, and their fermentation performances were determined. Five genetically different strains were selected for mixed fermentations with S. cerevisiae. Two types of inoculation were carried out: coinoculation and sequential inoculation. A balance between the two species was generally observed for the first 6 days, after which the levels of C. zemplinina started to decrease. Relevant differences were observed concerning the consumption of sugars, the ethanol and glycerol content, and acetic acid production, depending on which strain was used and which type of inoculation was performed. Sequential inoculation led to the reduction of about half of the acetic acid content compared to the pure S. cerevisiae fermentation, but the ethanol and glycerol amounts were also low. A coinoculation with selected combinations of S. cerevisiae and C. zemplinina resulted in a decrease of ~0.3 g of acetic acid/liter, while maintaining high ethanol and glycerol levels. This study demonstrates that mixed S. cerevisiae and C. zemplinina fermentation could be applied in sweet wine fermentation to reduce the production of acetic acid, connected to the S. cerevisiae osmotic stress response.

Microbiological and chemical profiles of naturally fermented table olives and brines from different Italian cultivars.

Six naturally fermented (Greek-style) table olives of cultivars Itrana, Peranzana, Cellina di Nardò, Nocellara del Belice and Bella di Cerignola, as well as their corresponding brines, were studied by a combined strategy consisting of chemical, microbiological and molecular analyses. In particular, organic acids, sugars, polyphenols, fatty acids, biogenic amines and cultivable microbiota were detected by standard methods. Moreover, tyramine and histamine producing bacteria were evaluated by an original approach consisting of Reverse-Transcription (RT)-qPCR. At the end of the fermentation process, mesophilic lactobacilli and yeasts in brine represented the dominating biota, ranging from 6.25 to 7.84 log CFU/ml and from 6.5 to 7.56 log CFU/ml, respectively. Enterobacteriaceae and pathogens were undetectable in all the samples. In general, table olive preparations differed in chemical composition. In particular, C16:0 and C18:2c9,12 concentrations ranged from 9.9 to 18.8 % and from 5.4 to 15.4 % of total fatty acids, respectively. The main fatty acid detected was C18:1c9 while CLAc9, t11 was present only in traces. Polyphenol concentrations greatly differentiated the final product, depending on the cultivar. A low quantity of biogenic amines was found in some samples and biogenic amines producing bacteria were rapidly detectable by RT-qPCR.

Diversity of Candida zemplinina strains from grapes and Italian wines.

The aim of this research was to genetically and technologically characterize Candida zemplinina strains isolated from different sources of enological interest. Phenotypic and genotypic subtyping, as well as enological characterization, were carried out on 36 C. zemplinina isolates collected from grapes, must and wines of different regions of Italy. RAPD-PCR fingerprinting of the isolates revealed a high genetic heterogeneity. At physiological level, yeasts were grouped into different clusters on the basis of sugar and ethanol tolerance. Common enological characteristics were examined and strains resulted to be highly fructophilic while presenting low ethanol and acetic acid production, high glycerol production, capacity to metabolize malic acid and slower fermentation kinetics when compared to Saccharomyces cerevisiae. The genetic and phenotypic intraspecies biodiversity of C. zemplinina gave useful data to understand its potential technological role in winemaking. This research represents a first step for the selection of C. zemplinina strains to be used as a starter in co-culture or in sequential inoculation with S. cerevisiae to improve the complexity and to enhance the particular characteristic of wines.

Biogenic amine content and microbiological profile of Pecorino di Farindola cheese.

"Pecorino di Farindola" is a traditional ewes' milk cheese produced in the Abruzzo region (Italy) and ripened for a minimum of 90 days. The main objective of this research was to characterize the microbiological and chemical composition of this cheese, manufactured in ten dairy farms during the winter cheese-making season (December through March). By using classical enumeration system on specific media variability was observed in the viable numbers of aerobic mesophilic bacteria, enterobacteria, coagulase-negative staphylococci, yeasts, enterococci, mesophilic and thermophilic lactobacilli, lactococci and thermophilic streptococci. Salmonella spp., Listeria monocytogenes and Escherichia coli O157:H7 resulted to be absent in all the samples. Among compounds possibly impacting on human health, the isomer cis-9, trans-11 conjugated linoleic acid (CLA), was determined in high levels in all samples, ranging from 9.2 to 12.7 mg/g fat. Great diversity was also found in biogenic amine contents with a relevant presence of tyramine in all the cheeses. This work represents the first study on Pecorino di Farindola cheese and could contribute to deepen the knowledge on its microbiological and biochemical features, focusing on hygiene and consumer health aspects.

Microbiological characteristics of kumis, a traditional fermented Colombian milk, with particular emphasis on enterococci population.

Kumis is a traditional fermented cow milk produced and consumed in South West Colombia. The main objective of this research was to studied the enterococcal population, present in 13 kumis samples traditionally manufactured, for their role as beneficial organisms or opportunistic pathogens. The molecular identification of 72 isolates evidenced that Enterococcus faecalis and E. faecium were the dominant species. The genes gelE, esp, asa1, cyl and hyl, all associated with virulence factors in enterococci, were detected in 30 isolates, while 42 were free of virulence determinants. Skim milk media were fermented by all the different isolates and further tested for proteolysis (free NH(3) groups), Angiotensin-I Converting Enzyme (ACE) inhibitory activity and biogenic amines production. Nine E. faecalis and two E. faecium strains produced fermented milk with ACE-inhibitory activity values ranging from 39.7% to 84.35% .The digestion of fermented milk samples by pepsin and pancreatin evidenced an increase in ACE inhibitory activity, with E. faecalis KE09 as the best producer (IC50 = 14.25 µg ml(-1)). Moreover, the strains showed a very low tyrosine decarboxylase activity and did not produce histamine during 48 h fermentation in milk. This study underlines the that Colombian kumis is a good source of not virulent enterococci able to produce fermented milks with ACE-inhibitory activity.

Discovering the Influence of Microorganisms on Wine Color.

Flavor, composition and quality of wine are influenced by microorganisms present on the grapevine surface which are transferred to the must during vinification. The microbiota is highly variable with a prevalence of non-Saccharomyces yeasts, whereas Saccharomyces cerevisiae is present at low number. For wine production an essential step is the fermentation carried out by different starter cultures of S. cerevisiae alone or in mixed fermentation with non-Saccharomyces species that produce wines with significant differences in chemical composition. During vinification wine color can be influenced by yeasts interacting with anthocyanin. Yeasts can influence wine phenolic composition in different manners: direct interactions-cell wall adsorption or enzyme activities-and/or indirectly-production of primary and secondary metabolites and fermentation products. Some of these characteristics are heritable trait in yeast and/or can be strain dependent. For this reason, the stability, aroma, and color of wines depend on strain/strains used during must fermentation. Saccharomyces cerevisiae or non-Saccharomyces can produce metabolites reacting with anthocyanins and favor the formation of vitisin A and B type pyranoanthocyanins, contributing to color stability. In addition, yeasts affect the intensity and tonality of wine color by the action of ß-glycosidase on anthocyanins or anthocyanidase enzymes or by the pigments adsorption on the yeast cell wall. These activities are strain dependent and are characterized by a great inter-species variability. Therefore, they should be considered a target for yeast strain selection and considered during the development of tailored mixed fermentations to improve wine production. In addition, some lactic acid bacteria seem to influence the color of red wines affecting anthocyanins' profile. In fact, the increase of the pH or the ability to degrade pyruvic acid and acetaldehyde, as well as anthocyanin adsorption by bacterial cells are responsible for color loss during malolactic fermentation. Lactic acid bacteria show different adsorption capacity probably because of the variable composition of the cell walls. The aim of this review is to offer a critical overview of the roles played by wine microorganisms in the definition of intensity and tonality of wines' color.

Promoting Candida zemplinina adhesion on oak chips: A strategy to enhance esters and glycerol content of Montepulciano d'Abruzzo organic wines.

In this study cell surface hydrophobicity and the ability to adhere on abiotic surfaces (polystyrene plates, stainless steel and oak chips) of 10 Candida zemplinina strains were assessed. Moreover, the impact of C. zemplinina cells adhered on oak surface on fermentation kinetics and volatile profile of Montepulciano d'Abruzzo organic wines was evaluated. All strains showed a hydrophobic nature with a certain affinity for the apolar solvents tested (hexadecane and decane). In agreement with this data strains were able to adhere on abiotic surfaces in a strain dependent way. On polystyrene plates all strains mainly grew as planktonic cells. On stainless steel surfaces sessile cells ranged from 2.6 Log CFU/mL (SB2) to 4.1 Log CFU/mL (SB8), while on oak chips were about 2 log higher ranging from 4.3 Log CFU/mL (SB8) to 6.1 Log CFU/mL (SB10). Candida zemplinina sessile state resulted in an increase of glycerol (from 6.98 g/L to 11.92 g/L) and esters amount (from 55.47 g/L to 91.5 mg/L), and a reduction of ethanol content (from 14.13% to 9.12% v/v). As for esters, methyl vanillate, ethyl isobutyrate, and ethyl isovalerate were present only when C. zemplinina was adhered on oak chips. This study revealed that changes of concentrations in esters and glycerol content reflected the fermentation bioactivity of yeast cells attached on oak chips. Surface-adhered behaviours should be considered in the improvement of strategies for the development of high-quality organic wines and eventually obtain novel wine styles.

Yeast microbiota associated with spontaneous sourdough fermentations in the production of traditional wheat sourdough breads of the Abruzzo region (Italy).

The aims of this study were to describe the yeast community of 20 sourdoughs collected from central Italy and to characterize the sourdoughs based on chemical properties. A polyphasic approach consisting of traditional culture-based tests (spore-forming and physiological tests) and molecular techniques (PCR-RFLP, RAPD-PCR, PCR-DGGE) and chemical analysis (total acidity, acids, and sugar contents), was utilized to describe the yeast population and to investigate the chemical composition of the doughs. PCR-RFLP analysis identified 85% of the isolates as Saccharomyces cerevisiae, with the other dominant species being Candida milleri (11%), Candida krusei (2.5%), and Torulaspora delbrueckii (1%). RAPD-PCR analysis, performed with primers M13 and LA1, highlighted intraspecific polymorphism among the S. cerevisiae strains. The diversity of the sourdoughs from the Abruzzo region is reflected in the chemical composition, yeast species, and strain polymorphism. Our approach using a combination of phenotypic and genotypic methods identified the yeast species in the 20 sourdough samples and provided a complete overview of the yeast populations found in sourdoughs from the Abruzzo region.

Cell Wall Surface Properties of Kluyveromyces marxianus Strains From Dairy-Products.

Thirty-three Kluyveromyces marxianus strains were tested for the ability to form biofilm and mat structures in YPD and whey and for cell surface hydrophobicity. To identify genes potentially involved in adhesion properties, a RT-qPCR analysis was performed. Eight strains were able to adhere on polystyrene plates in both media and formed a mature mat structure. These strains showed a different level of hydrophobicity ranging from 55 to 66% in YPD and from 69 to 81% in whey. Four K. marxianus orthologs genes (FLO11, STE12, TPK3, and WSC4), known from studies in other yeast to be involved in biofilm formation, have been studied. FLO11 and STE12 showed the highest fold changes in all conditions tested and especially in whey: 15.05 and 11.21, respectively. TPK3 was upregulated only in a strain, and WSC4 in 3 strains. In YPD, fold changes were lower than in whey with STE12 and FLO11 genes showing the highest fold changes. In mat structures FLO11 and STE12 fold changes ranged from 3.6-1.3 to 2-1.17, respectively. Further studies are necessary to better understand the role of these genes in K. marxianus adhesion ability.

Accumulation γ-Aminobutyric Acid and Biogenic Amines in a Traditional Raw Milk Ewe's Cheese.

The influence of calf (R1), kid (R2) and pig (R3) rennets on microbiota, biogenic amines (BAs) and γ-aminobutyric acid (GABA) accumulation in raw milk ewe's cheeses was evaluated. Cheeses were investigated at different ripening times for their microbial composition, free amino acids (FAAs), BAs and GABA content. Moreover, the expression of tyrosine (tdc) and histidine (hdc) decarboxylases genes was evaluated by quantitative Real Time-Polymerase Chain Reaction (qRT-PCR). Microbial counts showed similar values in all samples. Pig rennet were cheeses were characterized by higher proteolysis and the highest values of BAs. The BAs detected were putrescine, cadaverine and tyramine, while histamine was absent. qRT-PCR confirmed this data, in fact hdc gene was not upregulated, while tdc gene expression increased over time in agreement with the increasing content of tyramine and the highest fold changes were detected in R3 cheeses. GABA showed the highest concentration in R2 cheeses reaching a value of 672 mg/kg. These results showed that the accumulation of BAs and GABA in Pecorino di Farindola is influenced by ripening time and type of coagulant. Further studies are required to develop starter cultures to reduce BAs content and improve health characteristics of raw milk ewe's cheeses.

Modeling the aminogenic potential of Enterococcus faecalis EF37 in dry fermented sausages through chemical and molecular approaches.

Amino acid decarboxylase activity of the Enterococcus faecalis strain EF37 was monitored during fermentation and ripening of a traditional dry fermented sausage from Northern Italy (Salame Veronese) by means of microbiological, chemical, and molecular approaches in relation to three technological factors: fermentation temperature, sodium chloride concentration, and amount of glucose added to the meat mixture. Besides the analytical determination of tyramine and phenylethylamine accumulation and the counts of enterococci, the presence and quantification of the tyrosine decarboxylase gene (tdc) and its mRNA transcript were also investigated by using real-time PCR. According to the mathematical models obtained, all of the three factors studied were statistically significant and microbiologically relevant for the early development of enterococci, although the fermentation temperature had a more relevant influence on the enterococcal viable cells of the ripened product. Sodium chloride concentration was the most determinant factor of the final tyramine and 2-phenylethylamine accumulation and also of the levels of tdc present in the final product. In contrast, an effect of glucose concentration on tdc expression was observed in the last period of ripening. Moreover, increasing amounts of sodium chloride and decreasing fermentation temperature resulted in a reduced tdc expression. This is the first time that bacterial tyrosine decarboxylase potential is directly examined through a molecular approach in a fermented meat. The quantification of tdc and its transcript can help to elucidate the critical steps and factors during food manufacturing at which bacterial aminogenesis is possible, thus allowing researchers to propose technological measures to control decarboxylase activities.

Rapid detection and quantification of tyrosine decarboxylase gene (tdc) and its expression in gram-positive bacteria associated with fermented foods using PCR-based methods.

In this study, PCR-based procedures were developed to detect the occurrence and quantify the expression of the tyrosine decarboxylase gene (tdc) in gram-positive bacteria associated with fermented foods. Consensus primers were used in conventional and reverse transcription PCR to analyze a collection of 87 pure cultures of lactic acid bacteria and staphylococci. All enterococci, Staphylococcus epidermidis, Lactobacillus brevis, Lactobacillus curvatus, and Lactobacillus fermentum strains and 1 of 10 Staphylococcus xylosus strains produced amplification products with the primers DEC5 and DEC3 in accordance with results of the screening plate method and with previously reported result obtained with high-performance liquid chromatography. No amplicons were obtained for tyramine-negative strains, confirming the high specificity of these new primers. A novel quantitative real-time PCR assay was successfully applied to quantify tdc and its transcript in pure cultures and in meat and meat products. This assay allowed estimation of the influence of different variables (pH, temperature, and NaCl concentration) on the tdc expression of the tyraminogenic strain Enterococcus faecalis EF37 after 72 h of growth in M17 medium. Data obtained suggest that stressful conditions could induce greater tyrosine decarboxylase activity. The culture-independent PCR procedures developed here may be used for reliable and fast detection and quantification of bacterial tyraminogenic activity without the limitations of conventional techniques.