Italian Dairy Products Research Articles

Comparison of methods to homogenize ricotta cheese samples for total solids determination

Ricotta cheese is an Italian dairy product obtained by heat-coagulation of the proteins in whey, resulting from cheese production. The homogenization method applied to collect ricotta cheese samples could affect the total solids (TS) contents of the products. The aim of this study was to determine the effects of 5 different homogenization methods of the samples collection applied for the accuracy in TS determination in ricotta cheese, including un-homogenized method (UNH), un-homogenized combined with the Ultra-Turrax (IKA-Werke GmbH & Co. KG) method (UNH-UTX), spoon-homogenized method (SPN), spoon-homogenized combined with Ultra-Turrax method (SPN-UTX), and Ultra-Turrax homogenized method (UTX). The repeatability and the standard deviation of repeatability are indicators of agreement between repeated measures for TS contents. Results reported that UNH ricotta cheese samples showed large variation in TS content with values ranging from 18.31% to 25.85% and a standard deviation of repeatability higher than 1%; SPN samples showed repeatability values higher than 0.35% and standard deviation of repeatability ranged until 1.36%, suggesting large variability even in this case; the Ultra-Turrax homogenization reported repeatability values lower than 0.1% and standard deviation of repeatability lower than 0.05%, indicating that this method provides repeatable measurements that may reduce the sources of uncertainty in TS determination.

Influence of milk quality and cheese-making procedure on functional fatty acid transfer in three Italian dairy products: Mozzarella, Raveggiolo and Ricotta

Cheese quality traits are affected firstly by milk quality and secondly by processing protocols. The cheese-making procedure plays an important role in the transfer of functional fat components from milk to cheese with important implications on the nutritive value of dairy products.To evaluate the influence of the cheese-making procedure, three fresh Italian cheeses from the same milk bulk, Mozzarella, Raveggiolo and Ricotta were processed and analyzed in terms of fatty acid transfer from milk to dairy products. The fatty acids were transferred with several differences. In particular, C14:0 (P = 0.0011) and C14:1 (P = 0.0007) showed the highest value in Raveggiolo while C16:0 was higher in Raveggiolo and Ricotta (P = 0.0002). Trans-monoene fatty acids have a detrimental effect on human health, however trans C18:1 isomers, from 6 to 10, and trans12 showed no significant differences in transfer from milk to dairy products. In contrast, vaccenic and linoleic acids, which are beneficial fatty acids for human health, were recovered in higher percentages in Raveggiolo than in Mozzarella and Ricotta (P = 0.0188 and P < 0.0001, respectively). The recovery of oleic acid, an antiatherogenic fatty acid, was higher in Ricotta (P < 0.0001). No effect on conjugated linoleic acid was found.

Impact of Freezing on the Microbiological Quality and Physical Characteristics of Buffalo Mozzarella Cheese.

Simple SummaryBuffalo Mozzarella cheese from Campania is made from the fresh milk of the Italian Mediterranean buffalo. In 1996, thanks to its distinctive characteristics (specific environmental conditions and production method), Regulation (EC) No. 1107/96 recognized it as a Protected Designation of Origin product. The limited availability of milk and the increased demand for buffalo mozzarella cheese, especially during the spring-summer period (when milk production is lowest), have induced the use of frozen milk or curd for its production. The aim of this research was to provide preliminary results about the effect of freezing on microbial communities of fresh buffalo milk, curd and Buffalo Mozzarella cheese, and on physical properties (whiteness, hardness, and oxidation state) of Buffalo Mozzarella cheese. The preliminary results obtained have allowed us to conclude that the freezing process if properly carried out, does not compromise the microbiological quality of the products but produces only slight changes of some physical properties.Buffalo Mozzarella cheese from Campania is one of the most worldwide appreciated Italian dairy products. The increased demand for buffalo dairy products and the limited availability of the finest buffalo milk has prompted the diffusion of illicit practices, such as the use of milk, curd, or other products that are frozen or bought at low cost. The aim of this research was to provide preliminary results about the trend of the microbial communities of buffalo milk, curd and Buffalo Mozzarella cheese, during freezing storage of eleven months. At the same time, the alterations of physical properties and the presence of the molecular marker “γ4-casein”, have been investigated. The results showed that freezing reduced the concentrations of the total bacterial count, Enterobacteriaceae, coliforms, Escherichia coli and yeasts in fresh milk and, the concentrations of the total bacterial count, coliforms, lactic acid bacteria and yeasts in mature curd. In the finished product, no notable decreases were observed, except for lactic acid bacteria. About the γ4-casein, no increase was observed in all matrices. These preliminary results allow us to conclude that the freezing process if properly carried out, does not compromise the microbiological quality and the physical properties of the Buffalo Mozzarella cheese.

A Food-Grade Resin with LDH–Salicylate to Extend Mozzarella Cheese Shelf Life

Mozzarella cheese can be considered by far the world’s most popular Italian dairy product. Extending the shelf life of mozzarella cheese is an important issue in the dairy industry due to the high risk of contamination by several bacteria species, including spoilage pseudomonads. In this work, active packaging was prepared by coating traditional polyethylene terephthalate (PET) containers of “ovoline” mozzarella cheese with a food-grade resin mixed with a layered double hydroxide (LDH) in which salicylate anion was intercalatedby ionic exchange.. This antimicrobial molecule is listed in EC-Directive 10/2011/EC of 14 January 2011. Morphological arrangement of the molecule into the LDH layers was evaluated by X-ray diffraction (XRD) and controlled release followed by UV spectroscopy. Then, active trays were used to pack the mozzarella cheeses stored for 20 days at 4 °C and under thermal abuse (15 °C). Samples from both conditions showed coliform reduction (by ca. 2 log CFU/g) throughout the storage period. Depending on temperature, total mesophilic aerobic bacteria, Pseudomonas spp., yeasts, and mold loads were reduced in the first 3 days; at 4 °C. Slower acidification and lower proteolysis were also found in treated samples in comparison to control ones. The fitting of the Gompertz function to coliforms and spoilage pseudomonads highlighted an increase in the shelf life of mozzarella cheese of ca. 2 days at 4 °C. These results suggest that salicylate–LDH-coated PET may be applied to extend the shelf-life of mozzarella cheese and also counteract its spoilage if accidental interruptions to refrigeration occur.

Effect of the manufacturing process on Fiore Sardo PDO cheese microstructure by multi-frequency NMR relaxometry

The quality of Fiore Sardo cheese, a traditional Italian dairy product, was analyzed by means of Multi-frequency Nuclear Magnetic (NMR) relaxometry. Specifically, ten cheese wheels were purchased from different production chains, either industrial (N = 5) or artisanal (N = 5) samples. The former came from large scale productions and the latter were produced by shepherds in small quantities and in very small dairy factories. A preliminary interlaboratory proficiency testing of Time Domain - NMR (TD-NMR, 20 MHz) relaxometry by five laboratories, consistently showed that product quality is significantly different in terms of molecular mobility according to their production chain (i.e. industrial or artisanal). More detailed information about cheese microstructure was obtained by Multi-frequency Fast Field Cycling NMR (FFC-NMR) at lower magnetic fields (0.01–10 MHz). According to the interpretative model adopted to describe FFC-NMR data, industrially processed cheeses showed a higher para-casein hydration, higher protein protons to water protons ratio and a higher disorder (lower fractal dimension df) than artisanal products. It is suggested that differences between artisanal and industrial cheeses generate from the processing steps preceding cheese maturation, and are clearly reflected in the visual appearance of cheeses.This study shows that NMR relaxometry techniques can successfully discriminate Fiore Sardo cheese from different production chains, and paves the way for their implementation in quality control practices of dairy products.

Antilisterial Activity of Bacteriocins Produced by Lactic Bacteria Isolated from Dairy Products.

Sixty-nine Lactic Acid Bacteria (LAB) and bifidobacteria were isolated and identified from Italian dairy products (raw milk, cream, butter, soft cheese and yoghurt) to find new antimicrobial compounds to use as food bio-preservatives. All the isolates were preliminarily screened by the deferred antagonism method for bacteriocin production. Afterwards, to evaluate the release of bacteriocin in liquid medium, the Cell-Free Supernatant Fluid (CFSF) of the best producers was tested by agar well diffusion assay. The study allowed the selection of three bacteriocin producing strains (Enterococcus faecium E23, Bifidobacterium thermophilum B23 and Lactobacillus bulgaricus L21), endowed with the strongest and broadest inhibitory capability against the pathogen Listeria monocytogenes. The molecular characteristics and the chemical–physical properties of both producers and the respective bacteriocins were studied and compared. The results showed that E. faecium E23 was the best producer strain and its class IIa bacteriocins, called enterocin E23, exhibited a good spectrum of activity towards L. monocytogenes. Enterocin E23 was stable over a wide range of pH and at low temperatures for at least four months and, for this reason, it can be employed in refrigerated foods for the control of L. monocytogenes, the major concern in dairy products.

Lactic acid bacteria isolated from traditional Italian dairy products: activity against Listeria monocytogenes and modelling of microbial competition in soft cheese

Several studies showed that lactic acid bacteria isolated from traditional cheeses produced in Calabria (Italy) inhibited in vitro the growth of different spoilage and/or pathogenic microorganisms. However, the activity of these autochthonous strains against Listeria monocytogenes has never been investigated. One hundred and fifteen lactic acid bacteria isolated from traditional Calabrian cheeses were screened for their technological characteristics and inhibiting action against Listeria monocytogenes in laboratory media. The anti-Listeria activity of representative strains was evaluated also in soft cheese during chilled storage. Bacterial interaction was studied using a competitive modelling approach based on Lotka-Volterra equations. Strains 29 (Lactobacillus sakei), 31 (Lactobacillus plantarum group), and 76 (Lactobacillus plantarum group) showed the best performances both in vitro and in soft cheese reducing the loads of Listeria monocytogenes from 0.5 to almost 1 Log CFU/g. Also considering their technological features, these strains could be used as adjunct cultures to improve the safety of finished products. The proposed competition model returned good predictions, especially after the application of the interspecific competition parameter β. This approach may be useful to understand the mechanisms of microbial competition in food.

Environmental hot-spots and improvement scenarios for Tuscan “Pecorino” cheese using Life Cycle Assessment

Abstract The agricultural sector released about 5.4 Gt CO2 eq in 2010, of which 57% was due to the livestock sector. Cattle are the main contributors (65%) to the livestock sector's emissions, while sheep and goats (small ruminants) are responsible for about 6.5%, corresponding to 475 million tonnes CO2 eq. The Life Cycle Assessment method has been largely adopted to assess the environmental impacts connected to the livestock sector and to related products. Despite this, very few pieces of research are specifically addressed to analysis of the environmental performances of sheep cheese and, particularly, to the proposal of improvement strategies that may allow the reduction of environmental impacts. In this context, the Life Cycle Assessment method is applied in order to assess the environmental hot-spots of Tuscan “Pecorino” cheese (a traditional Italian dairy product obtained from sheep milk processing) and to evaluate potential improvement scenarios. The analysis follows a “cradle to gate” approach by including the processes related to sheep breeding (intensive system), milk transport and cheese production. The functional unit selected is 1 kg of “Pecorino” cheese, packaged at dairy farm gate and ready to be distributed. Focusing on Climate Change impacts, the results highlight that the total impacts related to the functional unit are 22.13 kg CO2 eq. The environmental hot-spots are mainly connected to direct emissions from the sheep enteric fermentation and to the production of feed used in sheep breeding, as well as, to waste water treatment and electricity consumption during cheese production. The adoption of a different breeding system (from intensive to extensive) may represent a good improvement option for the reduction of environmental impacts related to the baseline system, as well as the utilisation of a photovoltaic system as an alternative energy source for production of the electricity used in the cheese production phase.

Genome comparison and physiological characterization of eight Streptococcus thermophilus strains isolated from Italian dairy products

Eight Streptococcus thermophilus strains of dairy origin isolated in Italy were chosen to investigate autochthonous bacterial diversity in this important technological species. In the present study a comparative analysis of all the 17 S. thermophilus genomes publicly available was performed to identify the core and the variable genes, which vary among strains from 196 to 265. Additionally, correlation between the isolation site and the genetic distance was investigated at genomic level. Results highlight that the phylogenetic reconstruction differs from the geographical strain distribution. Moreover, strain M17PTZA496 has a genome of 2.15 Mbp, notably larger than that of the others, determined by lateral gene transfer (including phage-mediated incorporation) and duplication events. Important technological characters, such as growth kinetics, bacteriocin production, acidification kinetics and surface adhesion capability were studied in all the Italian strains. Results indicate a wide range of variability in adhesion properties that significantly clustered strains into four groups. Genomic differences among strains in relation to these characters were identified but a clear correlation between genotype and phenotype was not always found since most of the genomic modifications arise from single nucleotide polymorphisms. This research represents a step forward in the identification of strains-specific functions in Streptococcus thermophilus and it has also the potential to provide valuable information to predict strain specific behaviors in industrial processes.

Candidate probiotic strains, with immunomodulatory and antioxidant effects, isolated from traditional Italian dairy products

Cancer is a multifactorial disease and inflammation could be the 10th hallmark of cancer. Increased systemic inflammation is almost, if not always, a sign of dysbiosis and increased translocation of of bacterial origin, such as endotoxin. Therefore, therapeutic manipulations of intestinal bacteria could reverse the inflammatory responses and restore mucosal homeostasis. Thus, we evaluated the role of a fresh Pasta Filata cheese of the Alto Molise area called “Stracciata”, made from milk of cows fed by grazing and with local dry forages, as a source of potentially probiotic microorganisms. Molecular characterization by sequencing of the 16S rRNA gene were carried out on all bacteria isolated from fresh Pasta Filata cheese manufactured with natural starter cultures. Transmembrane electrical potential (ΔΨ) assay, antioxidant system activity, Glutathione disulphide (GSSG)/reduced Glutathione (GSH) ratio and nucleotides pool were measured by fluorescence techniques and HPLC. Moreover, the ability of bacterial isolates to stimulate IL-10 and TNF-α production by human peripheral blood mononuclear cells (PBMC) was determined in vitro by ELISA kits. We demonstrate how bacteria isolate by Stracciata cheese or their metabolites regulate immunomodulatory effects. Further studies are opportune for conferring therapeutic strategies to traditional dairy products in bacteria-metabolite-immune system axis contest.

Changes in oxidation-reduction potential during milk fermentation by wild lactic acid bacteria.

Oxidation-reduction potential (E h) is a fundamental physicochemical property of lactic acid bacteria that determines the microenvironment during the cheese manufacture and ripening. For this reason the E h is of growing interest in dairy research and the dairy industry. The objective of the study was to perform a comprehensive study on the reduction activity of wild lactic acid bacteria strains collected in different periods (from 1960 to 2012) from Italian dairy products. A total of 709 strains belonging to Lactococcus lactis, Enterococcus durans, E. faecium, E. faecalis and Streptococcus thermophilus species were studied for their reduction activity in milk. Kinetics of milk reduction were characterised by the minimum redox potential (E h7) and time of reaching E h7 (t min), the maximum difference between two measures (Δmax) and the time at which these maximum differences occurred (t*). Broad diversity in kinetic parameters was observed at both species and strain levels. E. faecalis and L. lactis resulted to be the most reducing species, while S. thermophilus was characterised by the lowest reducing power while the greatest heterogeneity was pointed out among E. durans and E. faecium strains. Considering the period of collection (1960-2012) we observed that the more recently isolated strains generally showed less reducing activity. This trend was particularly evident for the species E. durans, E. faecium and L. lactis while an opposite trend was observed in E. faecalis species. Data reported in this research provide new information for a deeper understanding of redox potential changes during milk fermentation due to bacterial growth. Gain knowledge of the redox potential of the LAB cultures could allow a better control and standardisation of cheesemaking process.

Physico-chemical characteristics and acidic profile of PDO Pecorino Romano cheese: Seasonal variation

Pecorino Romano, a protected designation of origin (PDO) semi-cooked hard cheese, is the best known Italian dairy product obtained from ovine milk and one of the most exported Italian cheeses in the world. The aim of this work was to provide useful information on physico-chemical and nutritional characteristics of PDO Pecorino Romano cheese taking into account the variability related to the season of cheese manufacture. A total of 70 samples of Pecorino Romano cheese, with a ripening time ranged from 7 to 8 months, and manufactured at different times of the year (from March to June) were analyzed. The month of production affected cheese composition, and cheeses produced in late winter and spring were characterized by a less fat and salt content and a higher protein content with respect to those produced in early summer. Also the biochemical processes of proteolysis and lipolysis were influenced by the seasonality of productions. In particular cheeses produced at late winter were more proteolyzed and lipolyzed if compared with those manufactured at summer season. The nutritional value of cheese fat, associated in particular with linolenic, rumenic and vaccenic acids content, decreased with the progress of season probably due to variation in animal feed, pasture availability and fatty acids composition of grass lipids.

Physicochemical composition, fatty acid profile and cholesterol content of “Pecorino Carmasciano” cheese, a traditional Italian dairy product

“Pecorino Carmasciano” (pecorino C) cheese is produced from the raw milk of Laticauda sheep in the Province of Avellino located in the northwest Campania Region of southern Italy. The objective of this study was to investigate some physicochemical properties, fatty acid profile and cholesterol content of Pecorino C cheese during a 354-day maturation period. Pecorino C was characterised by a relatively high content of monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid (PUFA) and by a favourable ratio of n-6 to n-3 fatty acids (2.25:1). Eicosapentaenoic acid (C20:5 n-3) and docosahexaenoic acid (C22:6 n-3), in particular, were present at average amounts of 0.26% and 0.21% respectively. The total conjugated linoleic acid was 0.5%. High cholesterol values were not found during ripening time. This study is the first comprehensive report on the chemical and physical properties of Pecorino C cheese.

Effect of whey concentration on protein recovery in fresh ovine ricotta cheese

Ricotta cheese, particularly the ovine type, is a typical Italian dairy product obtained by heat-coagulation of the proteins in whey. The aim of this work was to investigate the influence of whey protein concentration, obtained by ultrafiltration, on yield of fresh ovine ricotta cheese. Ricotta cheeses were obtained by thermocoagulation of mixtures with protein content of 1.56, 3.10, 4.16, and 7.09g/100g from the mixing of skim whey and ultrafiltered skim whey. A fat-to-protein ratio of 1.1 (wt/wt) was obtained for all mixtures by adding fresh cream. The initial mixtures, as well as the final ricotta cheeses, were analyzed for their composition and by SDS-PAGE. Protein bands were quantified by QuantityOne software (Bio-Rad, Hercules, CA) and identified by liquid chromatography-tandem mass spectrometry. Significant differences in the composition of the ricotta cheese were observed depending on protein concentration. Particularly, ricotta cheese resulting from the mixture containing 7.09g/100g of protein presented higher moisture (72.88±1.50g/100g) and protein (10.18±0.45g/100g) contents than that prepared from the mixture with 1.56g/100g of protein (69.52±1.75 and 6.70±0.85g/100g, respectively), and fat content was lower in this sample (12.20±1.60g/100g) compared with the other treatments, with mean values between 15.72 and 20.50g/100g. Each protein fraction presented a different behavior during thermocoagulation. In particular, the recovery of β-lactoglobulin and α-lactalbumin in the cheese increased as their content increased in the mixtures. It was concluded that concentrating ovine rennet whey improved the extent of heat-induced protein aggregation during the thermal coagulation process. This resulted in a better recovery of each protein fraction in the product, and in a consequent increase of ricotta cheese yield.

Short communication: Characterization of Shiga toxin 2-carrying bacteriophages induced from Shiga-toxigenic Escherichia coli isolated from Italian dairy products

Forty samples of raw milk cheese and 25 samples of raw milk itself were subjected to enrichment culture for Shiga-toxigenic Escherichia coli (STEC), and a single Shiga toxin 2- (Stx2) positive strain was obtained from one of the cheese samples. Thus, aged cheeses in which the curd is subsequently heat treated (48°C) cannot be presumed to be STEC free. Infective Stx2 bacteriophages were induced from 3 STEC strains isolated elsewhere from raw milk and 1 STEC strain from aged cheese sourced in Italy. Data on E. coli host range, morphology, genome size, and genetic variation determined by restriction fragment length polymorphism and multi-locus genotyping are presented. Although all 4 bacteriophages were found to be short-tailed Podoviridae, they exhibited considerable variation in both genome size and content. This extended to the Stx2 genes themselves, whose sequences contained several point mutations, but these did not translate to amino acid substitutions.

Characterization of Staphylococcus aureus strains isolated from Italian dairy products by MALDI‐TOF mass fingerprinting

Staphylococcus aureus is a known pathogen, causing serious food-borne intoxications due to the production of enterotoxins, being otherwise a major cause of mastitis. In this sense, the detection of S. aureus is an important issue for the food industry to avoid health hazards and economic losses. The present work applied MALDI-TOF MS for the classification of 40 S. aureus strains, 36 isolated from Italian dairy products and four from human samples. All isolated strains were clearly identified as S. aureus by their spectral fingerprints. The peak masses m/z 3444, 5031, and 6887 were determined to be specific biomarkers for S. aureus. Furthermore, clustering of the peak mass lists was successfully applied as a typing method, resulting in eight groups of strains. This is the first time that a detailed spectral comparison was carried out and characteristic peak masses were determined for every spectral group. Three strains exhibited a peak at m/z 6917 instead of m/z 6887, which was related to four polymorphisms in their 16S rRNA sequences. However, the grouping obtained by MALDI-TOF MS fingerprinting could not be related to toxin production or to the origin of the strains.

Fermented milks fromEnterococcus faecalisTH563 andLactobacillus delbrueckiisubsp.bulgaricusLA2 manifest different degrees of ACE-inhibitory and immunomodulatory activities

Milk proteins are precursors of biologically active components that are released by enzymatic proteolysis. Among the biological activities recognised in milk components, the angiotensin-I converting enzyme (ACE)-inhibitory and immunomodulatory activities are of great interest. In the present work the ACE-inhibitory and immunomodulatory activities were analysed in milks fermented by two bacterial strains isolated from Italian dairy products, Enterococcus faecalis TH563 or Lactobacillus delbrueckii subsp. bulgaricus (L. delb. bulgaricus) LA2. ACE-inhibitory activity was determined by an already established enzymatic method and immunomodulatory activity by the proliferation of bovine peripheral blood lymphocytes (BPBL) taken from nine cows. BPBL were incubated for 48 h with increasing concentrations of peptide fractions (< 5000 g·mol−1) extracted from the two fermented milks. Concanavalin A (conA), a known activator of lymphocyte proliferation, was used as a positive control. Fermentation products from E. faecalis TH563 showed a significantly (P < 0.05) greater ACE-inhibitory activity than that obtained by L. delb. bulgaricus LA2 (69.43 ± 3.12% vs. 60.86 ± 1.01%). The immunomodulatory activity showed a large interanimal variability. Peptide fractions from milk fermented by L. delb. bulgaricus LA2 significantly inhibited BPBL proliferation at concentrations of 5, 25 and 50 μg·mL−1 in the presence of conA (P < 0.01). E. faecalis TH563 did not significantly modify BPBL proliferation at any peptide concentration used. In conclusion, L. delb. bulgaricus LA2-fermented milk showed ACE-inhibitory and immunomodulatory activities, while E. faecalis TH563-fermented milk had high ACE-inhibitory activity, suggesting a possible use of these strains for determining bioactive properties in dairy products.

Phenotypic and Genotypic Characterization ofStaphylococcus aureusStrains from Italian Dairy Products

Staphylococcus aureus is a known major cause of foodborne illnesses, and milk and dairy products are often contaminated by enterotoxigenic strains of this bacterium. In the present study, 122 S. aureus isolates collected from different dairy products were characterised by phenotypic properties, by the distribution of genes encoding staphylococcal enterotoxins (sea, sec, sed, seg, seh, sei, sej, and sel) and by randomly amplified polymorphic DNA PCR (RAPD-PCR). Moreover, strain resistance to vancomycin and methicillin (oxacillin) was studied. The differences in the RAPD-PCR profiles obtained with the primers M13 and AP4 revealed the presence of a great genetic heterogeneity among the different S. aureus strains. Using the primer AP4 and M13, eight groups were distinguished by RAPD-PCR cluster analysis, although, except in few cases, it was not possible to correlate the isolates of different animal species (cow or ovine) with the presence of se genes. None of the isolates showed resistance to vancomycin or methicillin.

Molecular typing ofStaphylococcus aureusisolated from Italian dairy products on the basis of coagulase gene polymorphism, multiple-locus variable-number tandem-repeat and toxin genes

Coagulase gene restriction fragment length polymorphism (RFLP), six-locus variable-number tandem-repeat analysis patterns (MLVA) and detection of enterotoxin genes (se) (sea, sec, sed, seg, seh, sei, sej and sel) were used to determine the phylogenetic relationship among isolates of Staphylococcus aureus isolated from dairy products from different regions of Italy. A total of 25 Staph. aureus were subtyped into 16 coagulase genotypes by RFLP, and MLVA revealed marked genomic variability. Furthermore, 17 of the isolates harboured at least one toxin gene, with the predominance of sea, sed and sej among cow isolates and sec-sel among the goat and sheep strains. Combined RFLP, MLVA polymorphism and se genes were found to be useful techniques for discriminating several genetic variants in Staph. aureus isolates.

Technological and molecular characterisation of enterococci isolated from north–west Italian dairy products

Abstract In the present study, 68 enterococcal isolates collected from dairy products in north–west Italy were characterised by randomly amplified polymorphic DNA-PCR (RAPD-PCR) and by their technologically relevant biochemical properties. After the comparison of RAPD-PCR profiles with the profiles of the enterococcal type strains, isolates were assigned to the species Enterococcus faecalis (35 isolates), E. faecium (27 isolates) and E. durans (6 isolates). Phenotypic identification based on carbohydrate fermentation profile galleries gave different results from RAPD-PCR in 17.6% of the cases (10 E. faecium and 2 E. durans isolates). With respect to biochemical activities, the majority of the strains displayed weak acidification activity in milk. High values for redox activity were detected for 80% of E. faecalis isolates, while E. faecium provided the most lipolytic species. Proteolytic activity was generally low, except for 10 E. faecalis isolates that displayed values ⩾ 0.5 mg tyrosine 5 mL - 1 of milk. None of the isolates carried vanA or vanB (vancomycin resistance) genetic determinants.