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PubMed2004

Chemometric analysis of proteolysis during ripening of Ragusano cheese.

Chemometric modeling of peptide and free amino acid data was used to study proteolysis in Protected Denomination of Origin Ragusano cheese. Twelve cheeses ripened 3 to 7 mo were selected from local farmers and were analyzed in 4 layers: rind, external, middle, and internal. Proteolysis was significantly affected by cheese layer and age. Significant increases in nitrogen soluble in pH 4.6 acetate buffer and 12% trichloroacetic acid were found from rind to core and throughout ripening. Patterns of proteolysis by urea-PAGE showed that rind-to-core and age-related gradients of moisture and salt contents influenced coagulant and plasmin activities, as reflected in varying rates of hydrolysis of the caseins. Analysis of significant intercorrelations among chemical parameters revealed that moisture, more than salt content, had the largest single influence on rates of proteolysis. Lower levels of 70% ethanol-insoluble peptides coupled to higher levels of 70% ethanol-soluble peptides were found by reversed phase-HPLC in the innermost cheese layers and as the cheeses aged. Non-significant increases of individual free amino acids were found with cheese age and layer. Total free amino acids ranged from 14.3 mg/g (6.2% of total protein) at 3 mo to 22.0 mg/g (8.4% of total protein) after 7 mo. Glutamic acid had the largest concentration in all samples at each time and, jointly with lysine and leucine, accounted for 48% of total free amino acids. Principal components analysis and hierarchical cluster analysis of the data from reversed phase-HPLC chromatograms and free amino acids analysis showed that the peptide profiles were more useful in differentiating Ragusano cheese by age and farm origin than the amino acid data. Combining free amino acid and peptide data resulted in the best partial least squares regression model (R(2) = 0.976; Q(2) = 0.952) predicting cheese age, even though the peptide data alone led to a similarly precise prediction (R(2) = 0.961; Q(2) = 0.923). The most important predictors of age were soluble and insoluble peptides with medium hydrophobicity. The combined peptide data set also resulted in a 100% correct classification by partial least squares discriminant analysis of cheeses according to age and farm origin. Hydrophobic peptides were again discriminatory for distinguishing among sample classes in both cases.

Amino Acids↗
PubMed2004

Influence of adjunct cultures on volatile free fatty acids in reduced-fat Edam cheeses.

The effects of the adjunct cultures Lactococcus lactis ssp. diacetylactis, Brevibacterium linens BL2, Lactobacillus helveticus LH212, and Lactobacillus reuteri ATCC 23272 on volatile free fatty acid production in reduced-fat Edam cheese were studied. Lipase activity evaluation using p-nitrophenyl fatty acid ester substrates indicated that L. lactis ssp. diacetylactis showed the highest activity among the 4 adjunct cultures. Full-fat and 33% reduced-fat control cheeses (no adjunct) were made along with 5 treatments of reduced-fat cheeses, which included individual, and a mixture of the adjunct cultures. Volatile free fatty acids of cheeses were analyzed using static headspace analysis with 4-bromofluorobenzene as an internal standard. Changes in volatile free fatty acid concentrations were found in headspace gas of cheeses after 3-and 6-mo ripening. Acetic acid was the most abundant acid detected throughout ripening. Full-fat cheese had the highest relative amount of propionic acid among the cheeses. Certain adjunct cultures had a definite role in lipolysis at particular times. Reduced-fat cheese with L. lactis ssp. diacetylactis at 3-mo showed the highest levels of butyric, isovaleric, n-valeric, iso-caproic, and n-caproic acid. Reduced-fat cheese with Lactobacillus reuteri at 6 mo produced the highest relative concentration of isocaproic, n-caproic, and heptanoic, and the highest relative concentration of total acids.

Acetic Acid↗
PubMed2005

Compositional factors associated with calcium lactate crystallization in smoked Cheddar cheese.

Previous researchers have observed that surface crystals of calcium lactate sometimes develop on some Cheddar cheese samples but not on other samples produced from the same vat of milk. The causes of within-vat variation in crystallization behavior have not been identified. This study compared the compositions of naturally smoked Cheddar cheese samples that contained surface crystals with those of samples originating from the same vat that were crystal-free. Six pairs of retail samples (crystallized and noncrystallized) produced at the same cheese plant on different days were obtained from a commercial source. Cheese samples were 5 to 6 mo old at the time of collection. They were then stored for an additional 5 to 13 mo at 4 degrees C to ensure that the noncrystallized samples remained crystal-free. Then, the crystalline material was removed and collected from the surfaces of crystallized samples, weighed, and analyzed for total lactic acid, L(+) and D(-) lactic acid, Ca, P, NaCl, moisture, and crude protein. Crystallized and noncrystallized samples were then sectioned into 3 concentric subsamples (0 to 5 mm, 6 to 10 mm, and greater than 10 mm depth from the surface) and analyzed for moisture, NaCl, titratable acidity, L(+) and D(-) lactic acid, pH, and total and water-soluble calcium. The data were analyzed by ANOVA according to a repeated measures design with 2 within-subjects variables. The crystalline material contained 52.1% lactate, 8.1% Ca, 0.17% P, 28.5% water, and 8.9% crude protein on average. Both crystallized and noncrystallized cheese samples contained significant gradients of decreasing moisture from center to surface. Compared with noncrystallized samples, crystallized samples possessed significantly higher moisture, titratable acidity, L(+) lactate, and water soluble calcium, and significantly lower pH and NaCl content. The data suggest that formation of calcium lactate crystals may have been influenced by within-vat variation in salting efficacy in the following manner. Lower salt uptake by some of the cheese curd during salting may have created pockets of higher moisture and thus higher lactose within the final cheese. When cut into retail-sized chunks, the lower salt, higher moisture samples contained more lactic acid and thus lower cheese pH, which shifted calcium from the insoluble to the soluble state. Lactate and soluble calcium contents in these samples became further elevated at the cheese surface because of dehydration during smoking, possibly triggering the formation of calcium lactate crystals.

Calcium↗
PubMed2006

Triacylglycerol composition of protected designation of origin cheeses during ripening. Authenticity of milk fat.

Triacylglycerol (TAG) composition by carbon number in 2 protected designation of origin cheeses, Mahón (cheese from cow milk) and Manchego (cheese from ewe milk) that were manufactured by 3 different producers was analyzed during cheese ripening using gas chromatography with a short capillary column. The TAG composition at different times during cheese ripening was also analyzed in cheeses from different batches produced at the same plant. Lipolysis levels in the Mahón and Manchego cheeses during ripening were low; free fatty acid values ranged from 2,500 to 4,000 ppm at the end of ripening. The TAG composition did not change significantly during ripening. The TAG values obtained from each cheese sample were substituted into the multiple regression equations that have been proposed to detect foreign fats in milk fat. The values obtained using the equations for bovine (proposed by the European Union) and ovine milk (proposed by our laboratory) were within the normal range. Accordingly, these equations can be considered useful for detecting foreign fat in these cheeses during the ripening period contemplated during this study.

Animals↗
PubMed2006

A model system for studying the effects of colloidal calcium phosphate concentration on the rheological properties of Cheddar cheese.

A novel model system was developed for studying the effects of colloidal Ca phosphate (CCP) concentration on the rheological properties of Cheddar cheese, independent of proteolysis and any gross compositional variation. Cheddar cheese slices (disks; diameter = 50 mm, thickness = 2 mm) were incubated in synthetic Cheddar cheese aqueous phase solutions for 6 h at 22 degrees C. Control (unincubated) Cheddar cheese had a total Ca and CCP concentration of 2.80 g/100 g of protein and 1.84 g of Ca/100 g of protein, respectively. Increasing the concentration of Ca in the synthetic Cheddar cheese aqueous phase solution incrementally in the range from 1.39 to 8.34 g/L significantly increased the total Ca and CCP concentration of the cheese samples from 2.21 to 4.59 g/100 g of protein and from 1.36 to 2.36 g of Ca/100 g of protein, respectively. Values of storage modulus (index of stiffness) at 70 degrees C increased significantly with increasing concentrations of CCP, but the opposite trend was apparent at 20 degrees C. The maximum in loss tangent (index of meltability/flowability) decreased significantly with increasing concentration of CCP, and there was no significant effect on the temperature at which the maximum in loss tangent occurred (68 to 70 degrees C). Fourier transform mechanical spectroscopy showed the frequency dependence of all of the cheese samples increased with increasing temperature; however, solubilization of CCP increased the frequency dependence of the cheese matrix only in the high temperature region (i.e., >35 degrees C). These results support earlier studies that hypothesized that the concentration of CCP strongly modulates the rheological properties of cheese.

Calcium Phosphates↗
PubMed2006

Major advances in concentrated and dry milk products, cheese, and milk fat-based spreads.

Advances in dairy foods and dairy foods processing since 1981 have influenced consumers and processors of dairy products. Consumer benefits include dairy products with enhanced nutrition and product functionality for specific applications. Processors convert raw milk to finished product with improved efficiencies and have developed processing technologies to improve traditional products and to introduce new products for expanding the dairy foods market. Membrane processing evolved from a laboratory technique to a major industrial process for milk and whey processing. Ultra-filtration and reverse osmosis have been used extensively in fractionation of milk and whey components. Advances in cheese manufacturing methods have included mechanization of the making process. Membrane processing has allowed uniform composition of the cheese milk and starter cultures have become more predictable. Cheese vats have become larger and enclosed as well as computer controlled. Researchers have learned to control many of the functional properties of cheese by understanding the role of fat and calcium distribution, as bound or unbound, in the cheese matrix. Processed cheese (cheese, foods, spreads, and products) maintain their importance in the industry as many product types can be produced to meet market needs and provide stable products for an extended shelf life. Cheese delivers concentrated nutrients of milk and bio-active peptides to consumers. The technologies for the production of concentrated and dried milk and whey products have not changed greatly in the last 25 yr. The size and efficiencies of the equipment have increased. Use of reverse osmosis in place of vacuum condensing has been proposed. Modifying the fatty acid composition of milkfat to alter the nutritional and functional properties of dairy spread has been a focus of research in the last 2 decades. Conjugated linoleic acid, which can be increased in milkfat by alteration of the cow's diet, has been reported to have anticancer, anti-atherogenic, antidiabetic, and antiobesity effects for human health. Separating milk fat into fractions has been accomplished to provide specific fractions to improve butter spreadability, modulate chocolate meltability, and provide texture for low-fat cheeses.

Animals↗
PubMed2006

Utilization of fourier transform infrared spectroscopy for measurement of organic phosphorus and bound calcium in cheddar cheese.

The methods available for measuring organic P and bound Ca in cheese are either cumbersome or involve dilution of the cheese. Dilution of the cheese can lead to erroneous results, particularly in the case of bound Ca. Hence, the objective of this study was to evaluate the feasibility of Fourier transform infrared (FTIR) spectroscopy for direct measurement of organic P and bound Ca in Cheddar cheese. Two hundred sixteen samples of cheese were analyzed for protein-bound organic P, bound Ca using a water-extraction based method, and buffering curves. Additionally, the infrared spectra of the cheeses were collected between 4,000 and 650 cm(-1), at a resolution of 4 cm(-1), and 256 scans per sample. The spectral shifts in the infrared region from 1,050 to 900 cm(-1), in addition to the measured concentrations of organic P, bound Ca, and buffering peak area at pH 5.1, were used to develop calibration models using partial least squares (PLS) regression analysis. The spectral region of 956 to 946 cm(-1) correlated with the measured concentrations of organic P and the overall PLS model had a correlation (R2) of 0.76 between the predicted and measured concentrations. The spectral region at approximately 980 cm(-1) was correlated with the measured concentrations of bound Ca, and the overall PLS model had a correlation (R2) of 0.70 between the predicted and measured concentrations. A similar spectral region at approximately 980 cm(-1) was also correlated with the measured buffering peak areas and the overall PLS model had a correlation (R2) of 0.64 between the predicted and measured peak areas. A linear regression analysis between the bound Ca and buffering peak area demonstrated that bound Ca was correlated (R2 = 0.73) with buffering peak area. This study demonstrates that FTIR can be used to measure organic P in cheeses. It also has the potential to be used for measuring bound Ca in undiluted cheeses, and for prediction of the buffering capacity of cheese.

Buffers↗
PubMed1990

Factors controlling histamine production in Swiss cheese inoculated with Lactobacillus buchneri.

Swiss cheese was made from raw milk inoculated with various concentrations of a histamine-producing strain of Lactobacillus buchneri. Histamine production in these cheeses was proportional to the initial number of L. buchneri present in the raw milk. The highest inoculum level tested was 10(5) L. buchneri/ml. This cheese contained 80 mg of histamine/100 g of cheese after 90 d of storage. Only 15 mg of histamine/100 g of cheese were detected after 90 d at the lowest inoculum level, 10(2) L. buchneri/ml. No histamine was detected in any of the Swiss cheese samples until after the brining stage. Perceptible growth of L. buchneri also did not occur until after the warm room treatment. Therefore, control of histamine formation in Swiss cheese requires control of the number of histamine-producing bacteria in the raw milk. A 5.5% NaCl concentration in DeMan, Rogosa, Sharpe (MRS) broth inhibited the production of histamine by L. buchneri, but the concentrations of NaCl typically found in Swiss cheese were not inhibitory. The histamine-producing isolate of L. buchneri survived heating at 49 to 80 degrees C for 10 min, suggesting that this organism would easily survive the normal heating process applied to raw milk used prior to making Swiss cheese.

Animals↗
PubMed2000

Formation of biogenic amines in raw milk Hispánico cheese manufactured with proteinases and different levels of starter culture.

Two proteinases, a neutral proteinase from Bacillus subtilis and a cysteine proteinase from Micrococcus sp., were used to accelerate the ripening process of raw cow's milk Hispánico cheese, a semihard variety. Two levels (0.1% and 1%) of a commercial starter culture containing Lactococcus lactis subsp. lactis and L. lactis subsp. cremoris were added for cheese manufacture. The influence of both factors, proteinase addition and level of starter culture, on the growth of amino acid-decarboxylating microorganisms and on the formation of biogenic amines during cheese ripening was investigated in duplicate experiments. The population of tyrosine decarboxylase-positive bacteria, which represented less than 1% of the total bacterial population in most cheese samples, and tyrosine decarboxylase-positive lactobacilli was not influenced by proteinase addition or level of starter culture. Tyramine was detected in all batches of cheese from day 30. Its concentration was significantly (P < 0.05) influenced by proteinase addition but not by the level of starter culture and increased with cheese age. After 90 days of ripening, 103 to 191 mg/kg of tyramine was found in the different cheese batches. Histamine was not detected until day 60 in cheese with neutral proteinase and 1% starter culture and until day 90 in the rest of the cheeses. The concentration of this amine did not exceed 20 mg/kg in any of the batches investigated. Phenylethylamine and tryptamine were not found in any of the samples.

Animals↗
PubMed2002

Laboratory-scale preparation of soft cheese artificially contaminated with low levels of Escherichia coli O157, Listeria monocytogenes, and Salmonella enterica serovars Typhimurium, Enteritidis, and Dublin.

The production of cheese with incurred low levels of pathogenic microorganisms stressed by the production process was the aim of the study. A standard protocol for the preparation of artificially contaminated soft cheese on a laboratory scale was developed. Milk for cheese preparation was artificially contaminated with pathogenic target microorganisms at low levels, between 1 and 10 CFU/ml. Two strains of Escherichia coli OI157:H7, two strains of Listeria monocytogenes, and three Salmonella spp. (Salmonella enterica serovars Typhimurium, Enteritidis, and Dublin) were investigated. The food pathogens in the cheese were exposed to the entire production process. All three microorganism species survived the cheese production process and were detected in the final product at concentrations between 1 and 50 CFU/g. The cheese produced contains target microorganisms that have been exposed to curd formation, drainage, setting, and ripening. This cheese can be used to validate microbiological methods or to examine the target microorganisms in a natural food environment at low concentrations. It represents an alternative to artificial contamination of cheese by adding target microorganisms to a final cheese product.

Animals↗
PubMed2002

Behavior of Escherichia coli O157:H7 during the manufacture and ripening of feta and telemes cheeses.

Pasteurized whole ewe's and cow's milk was used in the manufacture of Feta end Telemes cheeses, respectively, according to standard procedures. In both cases, the milk had been inoculated with Escherichia coli O157:H7 at a concentration of ca. 5.1 log CFU/ml and with thermophilic or mesophilic starter cultures at a concentration of ca. 5.3 to 5.6 log CFU/ml. In the first 10 h of cheesemaking, the pathogen increased by 1.18 and 0.82 log CFU/g in Feta cheese and by 1.56 and 1.35 log CFU/ g in Telemes cheese for the trials with thermophilic and mesophilic starters, respectively. After 24 h of fermentation, a decrease in E. coli O157:H7 was observed for all trials. At that time, the pH was reduced to 4.81 to 5.10 for all trials. Fresh cheeses were salted and held at 16 degrees C for ripening until the pH was reduced to 4.60. Cheeses were then moved into storage at 4 degrees C to complete ripening. During ripening, the E. coli O157:H7 population decreased significantly (P < or = 0.001) and finally was not detectable in Feta cheese after 44 and 36 days and in Telemes cheese after 40 and 30 days for the trials with thermophilic and mesophilic starters, respectively. The estimated times required for one decimal reduction of the population of E. coli O157:H7 after the first day of processing were 9.71 and 9.26 days for Feta cheese and 9.09 and 7.69 days for Telemes cheese for the trials with thermophilic and mesophilic starters, respectively.

Animals↗
PubMed1993

A linoleate-enriched cheese product reduces low-density lipoprotein in moderately hypercholesterolemic adults.

OBJECTIVE: To test the effect of substituting a modified-fat cheese product into the diets of hypercholesterolemic adults. DESIGN: A 4-month, randomized, double-blind, crossover substitution trial. SETTING: General community outpatient study. PARTICIPANTS: Twenty-six healthy adult volunteers (17 men, 9 women) with moderate hypercholesterolemia (total cholesterol > 5.69 mmol/L but < 7.24 mmol/L). INTERVENTION: Daily substitution of 100 g of cheese, either partial skim-milk mozzarella or modified-fat (vegetable oil) mozzarella cheese product, into participants' normal diets. Participants consumed an assigned cheese for 2 months, at which time they crossed over to consume the other study cheese. MAIN OUTCOME MEASURES: Plasma lipid and apolipoprotein levels were measured at baseline and at 2 and 4 months after initiation of the study. Compliance was assessed by body weight and by biweekly dietary records and interviews. RESULTS: No differences in weight or in the amount or type of calories consumed were found during the study. No statistically significant changes in lipid values resulted from consumption of mozzarella cheese. Modified-fat cheese substitution resulted in a decreased low-density lipoprotein cholesterol level when compared with levels at both baseline (-0.28 mmol/L; 95% Cl, -0.14 to -0.42 mmol/L) and during consumption of the skim-milk mozzarella cheese (-0.38 mmol/L; 95% Cl, -0.2 to -0.70 mmol/L). Findings for total cholesterol were similar. High-density lipoprotein cholesterol, plasma triglyceride, and apolipoprotein A-l and B-100 levels were unaltered. Both sexes responded similarly. CONCLUSIONS: A linoleate-enriched cheese product, in the absence of any other changes in diet or habits, substituted into the normal diets of hypercholesterolemic adults reduced low-density lipoprotein and plasma cholesterol levels.

Adult↗
PubMed1991

[The use of appropriate technologies to improve the sanitary quality and the yield of goat cheeses in little farms].

The purpose of this study was to increase the microbiological quality and yields of goat cheese prepared at farm level. For this purpose, appropriate technologies for the cheese-making process were designed, using a curd tank heated by gas, and cheese knives adjusted to the tank dimensions. Moreover, a low-cost table for whey draining and PVC moulds, were designed. Variables assayed were milk pasteurization, utilization of lactic acid starter by direct application, substitution of the kid rennet by commercial calf rennet, and cheese maturation for a one-month period. The control sample was goat cheese traditionally made by the small farmers. Processing and variables were evaluated by proximate chemical analysis, microbiological counts of aerobic mesophilic bacteria, total and fecal coliforms, and S. aureus; as well as by sensory evaluation of quality and acceptability. It was found that the cutting of curd with cheese knives significantly decreased solid losses in the whey. The addition of the starter and then the cheese maturation, as well as the use of the equipment previously described, increased the microbiological quality of cheese to standard sanitary regulation. Although pasteurization was the most effective treatment in decreasing bacteria contamination, this thermal treatment was difficult to be done under arid zones conditions. Commercial calf rennet did not differ significantly from kid rennet in the characteristics analyzed in this assay. Variables studied did not affect the normal sensory quality of goat cheese.

Animals↗
PubMedDate not supplied

Prevalence of cheese molars in eleven-year-old Dutch children.

In the Netherlands, first permanent molars with idiopathic enamel disturbances (IED) are called cheese molars. Though concern is expressed about their prevalence, adequate figures on the subject are missing. The porous enamel of cheese molars can be very sensitive to cold air and can decay rapidly. The aim of the present study was to investigate the prevalence in eleven-year-old Dutch children of cheese molars (IED). During an epidemiological study performed in four cities in the Netherlands, the first permanent molars and central incisors of eleven-year-old children were examined for hypoplasia, opacities, posteruptive enamel loss, premature extraction, and atypical restorations. The observation of a hypoplasia excluded the possibility of cheese molar. A total of 497 children were examined. Six percent (n = 128) of the molars (n = 1988) showed signs of IED (cheese molars), 10 percent of the children had cheese molars of which 8 percent two or more. Incisors (4 percent) with opacities were found in 3 percent in combination with two or more cheese molars. Among the four cities, no significant differences in occurrence were found. The results of this study showed that in 10 percent of the Dutch children eleven years of age, cheese molars (IED) were found. The cause for the phenomenon called cheese molars appears to be child centered. Further studies on prevalence, causes and prevention are mandatory.

Chi-Square Distribution↗
PubMed2000

Determination of cow's milk and ripening time in nonbovine cheese by capillary electrophoresis of the ethanol-water protein fraction.

A novel method is reported for analyzing adulteration of goat and ewe cheeses with cow's milk: capillary zone electrophoresis (CZE) in isoelectric, acidic buffers (50 mM imino diacetic acid, IDA, pH = pI 2.3). The cheese samples were extracted with a 20:80 v/v ethanol-water mixture in presence of 3 M urea and 1% beta-mercaptoethanol for 1 h. After centrifugation and lipid extraction, the samples were dissolved in 50 mM IDA, 6 M urea and 0.5% hydroxyethyl cellulose and analyzed by CZE at 700 V/cm. A total of 18 characteristic peaks were resolved among the three types of cheeses and 18 variables were defined as their respective areas. There was excellent similarity among the electrophoretic patterns obtained with cheeses of a given type of milk, while cheeses made with different types of milk were easily distinguishable. Most peaks were common to all cheeses, but the profile differed depending on the type of milk used. Principal component analysis, linear discriminant analysis, and partial least squares regression (PLS) were used for statistical analysis of the data obtained by CZE. In particular, by using PLS multivariate regression, the contents of cow's milk in presumably pure goat and ewe cheeses, as well as in binary and ternary mixtures, could be predicted with relative standard deviations of ca. 6-7%. In addition, the ripening time in goat and ewe cheeses could also be predicted.

Animals↗
PubMed1995

Chemical species in cheese and their origin in milk components.

Cheese making is the process of concentrating milk fat and protein by separation from water and soluble components. The objective of the cheese maker is to maximize yield efficiency by optimum utilization of each milk component while not compromising cheese quality. Cheese yielding potential of milk may be increased by selective breeding for specific protein genotypes, especially the BB variant of both kappa-casein and beta-lactoglobulin. Milk fat is included in cheese by occlusion into the protein coagulum. Participation of casein in both lactic and rennet coagulation is nearly complete so that casein losses to the whey occur mainly during cutting and the early stages of cooking. In lactic cheese, excepting cottage cheese, it is possible to eliminate losses of fines by centrifugal or membrane separation of curd. In heat-acid precipitated varieties protein recovery is increased by inclusion of whey proteins but fat recovery is very dependent on coagulation conditions. In ripened cheese obtaining the correct basic structure and composition is critical to texture and flavour development during curing.

Animals↗
PubMed1990

The occurrence of Listeria monocytogenes in cheese from a manufacturer associated with a case of listeriosis.

A case of listeriosis was associated with the consumption of a soft cheese produced in England. Goats cheese and other products from the same food manufacturer were examined for the presence of Listeria over the following 11 months. Listeria monocytogenes was isolated from 16 of 25 cheese samples on retail sale, 12 of 24 cheese samples obtained directly from the factory, and from shelving within the plant. Phage-typing of 68 isolates of L. monocytogenes from cheese samples and the factory showed that 66 (97%) were indistinguishable from the strain isolated from the patient's cerebrospinal fluid and stool. L. monocytogenes was not isolated from seven goats milk or two yoghurt samples. Listeria innocua was isolated from 10 cheese samples, two of which contained no other species of Listeria. Levels of L. monocytogenes shortly after production were low (less than 10/g), but were higher (10(5)-10(7) cfu/g) in six of the 16 cheese samples obtained from retail outlets. Multiplication of L. monocytogenes was demonstrated in cheeses contaminated at the factory and held at 4 degrees C in the laboratory.

Adult↗
PubMed2005

Survival of Escherichia coli O157:H7 in Galotyri cheese stored at 4 and 12 degrees C.

Post-process contamination of fresh acid-curd cheeses with Escherichia coli O157:H7 may pose a risk considering the low infectious dose and the ability of the pathogen to survive in acidic foods. To evaluate its survival in Galotyri, a traditional Greek acid-curd cheese, portions (0.5 kg) of two commercial fresh products, one artisan (pH 3.9+/-0.1) and the other industrial (pH 3.7+/-0.1), were inoculated with approximately 3.0 or 6.5 log cfu g(-1) of a five-strain cocktail of E. coli O157:H7, including rifampicin-resistant derivatives of the strains ATCC 43895 and ATCC 51657, and stored aerobically at 4 and 12 degrees C. Survival was monitored for 28 days by plating cheese samples on tryptic soy agar with 100 mg l(-1) rifampicin (TSA+Rif), SMAC and Fluorocult E. coli O157:H7 agar media. The pathogen declined much faster (P<0.05) in the industrial as compared to the artisan cheeses at both temperatures. Thus, while E. coli O157:H7 became undetectable by culture enrichment after 14 days at 4 degrees C in industrial samples, irrespective of the inoculation level, populations of 1.4-1.9 and 4.2-5.1 log cfu g(-1) survived after 28 days in the corresponding artisan cheeses with the low and high inocula, respectively. Survival was longer and greater (P<0.05) on TSA+Rif than on SMAC and Fluorocult, indicating the presence of acid-injured cells. Interestingly, survival of E. coli O157:H7 after 14-28 days in cheeses was better at 12 degrees C than at 4 degrees C, probably due to yeasts which grew on the surface of temperature-abused cheeses. The large difference in the pathogen's inactivation between the industrial and artisan cheeses at 4 degrees C could not be associated with major differences in pH or type/concentration of organic acids, suggesting another anti-E. coli O157:H7 activity by the industrial starter. The high survival of the pathogen in artisan Galotyri under conditions simulating commercial storage should be of concern.

Cheese↗