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PubMed1980

Investigations on formation and occurrence of volatile nitrosamines in Danish cheese.

The formation and occurrence of volatile nitrosamines in Danish cheese has been studied. The investigations showed that nitrosamines are evenly distributed within a given cheese and between cheeses from the same lot. No influence of production factors, such as nitrate addition, composition and type of cheese, storage or packaging conditions, could be demonstrated. Seventy-six percent of 156 samples of commercially produced Danish cheeses contained no nitrosamines ((detection limit 0.1 micrograms/kg). Trace amounts (0.1-0.3 micrograms/kg) of nitrosamines were found in 22% of the samples and 2% contained 0.6-0.7 micrograms/kg. Forty-two percent of 19 cheeses imported to Denmark contained no nitrosamines. Trace amounts of nitrosamines were found in 37% of the samples and 21% contained 0.4-3.6 micrograms/kg. Cheese samples from retail shops had slightly higher contents of nitrosamines than samples taken at dairy plants.

Animals↗
PubMed1994

Enamel rehardening with cheese in irradiated patients.

Radiotherapy of head and neck malignancies results in severe xerostomia which induces radiation caries. Hard cheese has potent anti-cariogenic effects, even with minimal salivary gland function. Eight patients irradiated for neck cancer volunteered for this study. The saliva flow rate varied between 0.0-0.15 ml/minute. In vitro etched enamel slabs, prepared from human teeth, were exposed intraorally to parafilm stimulated salivary secretion for 5 minutes or, alternatively, to cheese compounds and saliva due to masticating 20 gm hard cheese for 5 minutes. Microhardness measurements were carried out on the enamel surface at start (baseline), after etching and after rehardening. Stimulated saliva or cheese compounds and saliva, due to mastication, induced rehardening of surface enamel in both, non-irradiated and irradiated subjects. The rehardening was significantly increased in the irradiated group consuming cheese as compared to rehardening by stimulated saliva only and not significantly less of that achieved in non-irradiated subjects. Rehardening achieved with stimulated saliva in irradiated patients was of a borderline-significant lower degree in comparison to non-irradiated subjects. The reduced rehardening capacity of a decreased saliva flow in irradiated patients may be complemented by cheese compounds. For xerostomic patients, hard cheese consumption may be regarded as effective to keep initial caries under control.

Cariostatic Agents↗
PubMed1995

[Level of histamine and tyramine in ripening cheeses].

Histamine poisoning is a foodborne chemical intoxication resulting from the ingestion of food products containing high levels of histamine. Historically, histamine poisoning has been attributed to the consumption of fish species belonging to the Scomberesocidae and Scombridae families and other sea fish, but histamine poisoning outbreaks may occur after the consumption of cheese, or other types of fermented foods. Also tyramine has been proved as a cause of adverse reactions, involving headache, hypertensive crisis and interactions with antidepressive drugs, which were observed after consumption of ripening cheeses. The formation of high levels of histamine and tyramine in foods is directly correlated to the level of microorganisms, possessing the enzymes: histidine and tyrozyne decarboxylases, and also with the concentration of histidine and tyrosine free substrate. Proteolysis, which takes place during ripening of cheeses may play role in the release of free histidine and tyrosine. This study reports on the levels of histamine and tyramine in ripening cheeses taken from Polish food market. 43 samples of soft and hard cheeses were investigated. Histamine was measured according to the AOAC fluorometric method. Tyramine was measured after column separation and purification, according to the spectrofluorometric technique with 1-nitroso-2-ortophtalate aldehyde, according to Carou with couple of modifications by authors. Histamine levels ranged from 0 to 157 mg/kg and tyramine levels ranged from 3.8 to 575 mg/kg. The very high levels of histamine and tyramine in many samples of cheeses support the opinion, that sometimes the storage temperature has not been sufficient to stop bacterial multiplication and in consequence enzymatic activity of decarboxylases of native amino acids--precursors of biogenic amines in ripening cheeses.

Cheese↗
PubMed1992

Fungal contamination of Kashar cheese in Turkey.

Fifty random samples of Kashar cheese were collected from shops in different localities in Erzurum, all contained moulds. Mean count of total surface mould was 3.02 x 10(10)/g cheese and that of inner mould was 3.02 x 10(3)/g cheese. The genera Penicillium, Aspergillus, Mucor, Rhizopus and Geotrichum sp. were isolated from cheese samples. Aflatoxins were not detected in cheese samples. Potassium sorbate inhibited mould growth and sporulation in YES broth. The public health importance and economic significance of fungal contamination, and suggested measure for cheese quality are discussed.

Aflatoxins↗
PubMed1996

Sterigmatocystin: incidence, fate and production by Aspergillus versicolor in Ras cheese.

The occurrence, distribution, and stability of sterigmatocystin (STG) in Ras cheese were investigated. An incidence value for STG in market samples of Ras cheese was 35% with a mean value of 22.2 micrograms/kg. In experimental Ras cheese from milk contaminated with STG, 80% of the toxin was retained in the curd while 20% was found in the whey. The temperature for cheese ripening affected the toxin content. At 6 degrees C the toxin concentration was hardly affected, but at 20 degrees C the concentration was reduced by 16% after 90 days. In Ras cheese contaminated with spores of Aspergillus versicolor, toxin production started after 45 days of the ripening, reached a maximum after 90 days, and declined thereafter. Cow's milk favoured toxin formation in comparison with buffalo's milk. Aged cheese (more than 6 months) inhibited toxin production.

Animals↗
PubMed2006

Kluyveromyces lactis and Saccharomyces cerevisiae, two potent deacidifying and volatile-sulphur-aroma-producing microorganisms of the cheese ecosystem.

Cheese flavour is the result of complex biochemical transformations attributed to bacteria and yeasts grown on the curd of smear-ripened cheeses. Volatile sulphur compounds (VSCs) are responsible for the characteristic aromatic notes of several cheeses. In the present study, we have assessed the ability of Kluyveromyces lactis, Kluyveromyces marxianus and Saccharomyces cerevisiae strains, which are frequently isolated from smear-ripened cheeses, to grow and deacidify a cheese medium and generate VSCs resulting from L-methionine degradation. The Kluyveromyces strains produced a wider variety and higher amounts of VSCs than the S. cerevisiae ones. We have shown that the pathway is likely to be proceeding differently in these two yeast genera. The VSCs are mainly generated through the degradation of 4-methylthio-oxobutyric acid in the Kluyveromyces strains, in contrast to the S. cerevisiae ones which have higher L-methionine demethiolating activity, resulting in a direct conversion of L-methionine to methanethiol. The deacidification activity which is of major importance in the early stages of cheese-ripening was also compared in S. cerevisiae and Kluyveromyces strains.

Cell-Free System↗
PubMed1995

Potential growth and control of Escherichia coli O157:H7 in soft hispanic type cheese.

This study examined growth and control of two enterohemorrhagic Escherichia coli serotype O157:H7 strains in a soft Hispanic type cheese (Queso Fresco). Cheese was made in the laboratory using a commercial procedure and after inoculation it was stored under vacuum at temperatures ranging from 8 to 30 degrees C. The minimum temperature that allowed growth of E. coli in the unmodified normal cheese (pH 6.6) was 10 degrees C. No growth of either strains was observed during a 2 month storage period at 8 degrees C. Accumulated data from the growth studies were used for development of models relating square root of 1/LT (LT = lag time) and specific growth rate, to temperature. The effect of selected antimicrobials (potassium sorbate, sodium benzoate, and sodium lactate) added to milk or cheese on the growth and survival of these pathogens at various storage temperatures was also evaluated. Addition of sodium benzoate (0.3%) to cheese (pH 6.6) or addition of potassium sorbate (0.3%) to cheese (pH 6) made from milk acidified to pH 5.9 with propionic acid, had a significant impact on delaying or preventing growth of the pathogens.

Animals↗
PubMed1995

Occurrence of Listeria monocytogenes in soft and semi-soft cheeses in retail outlets in Sweden.

Samples of 333 retail cheeses produced in or imported into Sweden were examined for the presence of Listeria monocytogenes. Listeria monocytogenes was isolated from 6% of the cheese samples. Cheeses made from raw milk were more frequently contaminated with L. monocytogenes (42%) than cheeses made from heat-treated milk (2%). The incidence of the organism in whole cheeses and pre-cut wedges was similar (6%). L. monocytogenes was only found in imported cheeses (18 from France, and one from Germany and Italy, respectively). The numbers of L. monocytogenes varied from < 1 x 10(2) to 1 x 10(5) cfu/g. All L. monocytogenes strains belonged to serogroup 1/2, except isolates from two samples that belonged to serogroup 4.

Cheese↗
PubMed2004

Comparison of selective and nonselective primary enrichments for the detection of Listeria monocytogenes in cheese.

A completely selective enrichment procedure was compared with two partially nonselective ones for the detection of Listeria monocytogenes in cheeses. After enrichment for approximately 48 h, the enrichment media were streaked on selective agars and presumptive Listeria colonies were confirmed using PCR. In some cases, PCR was also performed directly on the enrichment broth. The conventional, completely selective enrichment procedure was not always the best choice for the detection of stressed L. monocytogenes in cheeses. Especially in the case of semi-hard cheeses from pasteurized milk and soft cheeses of the blue veined and the red smear types, the methods that incorporated a nonselective enrichment step gave better results than the completely selective method. For mold ripened, soft cheeses, the results were highly dependent on the brand of cheese and time of sampling, but the best results were obtained using the completely selective enrichment procedure.

Agar↗
PubMed2005

Relationships between sensorial characteristics and microbial dynamics in "Registered Designation of Origin" Salers cheese.

Raw milk cheeses show a wide diversity of sensorial characteristics, largely determined by the microflora of raw milk. Microbial dynamics in Registered Designation of Origin (R.D.O.) Salers cheese was assessed by DNA and RNA SSCP analysis on nine cheeses. These cheeses showed considerable diversity both in microbial dynamics and sensorial characteristics. Relationships between the sensorial characteristics and the microbial dynamics were studied. A global consideration of bacterial dynamics demonstrated that other bacteria than lactic acid bacteria can play a role in the elaboration of sensorial characteristics. Indeed, high CG% Gram-positive bacteria can be involved. DNA data, as well as RNA data, appeared relevant to attempts to explain sensorial variance. Correlations between sensorial and microbial data were rather complex. Several microbial variables for DNA and RNA analyses, noted at different times of analysis, were correlated to each sensory variable. A global view of cheese microbial community proved to be insufficient in explaining the diversity of the sensorial qualities of R.D.O. Salers cheese.

Cheese↗
PubMed2005

Interests in Geotrichum candidum for cheese technology.

The wide genotypic and phenotypic diversity of Geotrichum candidum strains does not facilitate its classification as yeast or a yeast-like fungus that is still a matter of debate. Whatever its classification, G. candidum possesses many different metabolic pathways that are of particular interest to the dairy industry. G. candidum is of importance in the maturation of cheese, and much is known about its direct contribution to cheese ripening and flavour formation. Its diverse metabolic potential means that G. candidum can play an important role in the ripening of many soft and semi-hard cheeses and make a positive contribution to the development of taste and aroma. It may also influence the growth of other microorganisms, both valuable and detrimental. The significance of the presence of G. candidum in cheese depends on the particular type of production and on the presence of biotypes featuring specific types of metabolism. However, in situ metabolic pathways involved in cheese ripening and their regulations are mainly unknown. The information available provides a good understanding of the potential of G. candidum strains that are used in cheese manufacture, and permits a better choice of strain depending on the characteristics required. The biochemical activities of G. candidum and its application in the dairy industry are presented in this review.

Cheese↗
PubMed2005

Novel extraction strategy of ribosomal RNA and genomic DNA from cheese for PCR-based investigations.

Cheese microorganisms, such as bacteria and fungi, constitute a complex ecosystem that plays a central role in cheeses ripening. The molecular study of cheese microbial diversity and activity is essential but the extraction of high quality nucleic acid may be problematic: the cheese samples are characterised by a strong buffering capacity which negatively influenced the yield of the extracted rRNA. The objective of this study is to develop an effective method for the direct and simultaneous isolation of yeast and bacterial ribosomal RNA and genomic DNA from the same cheese samples. DNA isolation was based on a protocol used for nucleic acids isolation from anaerobic digestor, without preliminary washing step with the combined use of the action of chaotropic agent (acid guanidinium thiocyanate), detergents (SDS, N-lauroylsarcosine), chelating agent (EDTA) and a mechanical method (bead beating system). The DNA purification was carried out by two washing steps of phenol-chloroform. RNA was isolated successfully after the second acid extraction step by recovering it from the phenolic phase of the first acid extraction. The novel method yielded pure preparation of undegraded RNA accessible for reverse transcription-PCR. The extraction protocol of genomic DNA and rRNA was applicable to complex ecosystem of different cheese matrices.

Bacteria↗
PubMed2006

Levels of cystathionine gamma lyase production by Geotrichum candidum in synthetic media and correlation with the presence of sulphur flavours in cheese.

Geotrichum candidum is a cheese-ripening agent with the potential to produce sulphur flavour compounds in soft cheeses. We aimed to develop an alternative test for predicting the aromatic (sulphur flavours) potential of G. candidum strains in soft cheese. Twelve strains of G. candidum with different levels of demethiolase activity (determined by a chemical method) in YEL-met (yeast extract, lactate methionine) medium were studied. We investigated cgl (cystathionine gamma lyase) gene expression after culture in three media - YEL-met, casamino acid and curd media - and then carried out sensory analysis on a Camembert cheese matrix. We found no correlation between demethiolase activity in vitro and cgl gene expression. Sensory analysis (detection of sulphur flavours) identified different aromatic profiles linked to cgl expression, but not to demethiolase activity. The RT-PCR technique described here is potentially useful for predicting the tendency of a given strain of G. candidum to develop sulphur flavours in cheese matrix. This is the first demonstration that an in vitro molecular approach could be used as a predictive test for evaluating the potential of G. candidum strains to generate sulphur compounds in situ (Camembert cheese matrix).

Cheese↗
PubMed2004

Alteration of raw-milk cheese by Pseudomonas spp.: monitoring the sources of contamination using fluorescence spectroscopy and metabolic profiling.

Thirty Pseudomonas spp. strains isolated from milk, water, cheese centre and cheese surface in two traditional workshops manufacturing raw milk St. Nectaire cheese were characterised by fluorescence spectroscopy and Biolog metabolic profiling. Factorial discriminant analysis (FDA) of the two data sets revealed clear linkages between groups of isolates. In the first workshop, milk could be incriminated as the sole source of cheese contamination. In the second one, milk and cheese centre isolates were found similar but surface cheese contaminants could be linked to a secondary contamination originating from water. Thus, it is possible to characterise, differentiate and trace Pseudomonas spp. strains using the fluorescence and metabolic profiling techniques. In addition, the two data sets were found highly correlated by canonical correlation analysis (CCA). Fluorescence spectroscopy however showed several advantages because of its low cost and processing speed.

Animals↗
PubMed2002

The microdistribution of oxygen in Danablu cheese measured by a microsensor during ripening.

Profiles of oxygen in Danablu cheese at the age of 1-19 weeks were measured by using an oxygen microsensor. In a cheese ripened for 1 week, the percentage oxygen saturation decreased to 70% at 0.25-mm depth and further to 50% at 4-mm depth. In a more extended determination of oxygen profiles, the spatial and temporal development in the oxygen level was investigated at 5-mm resolution at the center and 5 mm from the edge of the cylindrical cheeses at a depth of 45 mm. Average oxygen saturation decreased from 63% to 0.1% at the centre and from 69% to 0.1% at the edge in cheeses from 1 to 19 weeks. In the cheeses ripened for more than 3 weeks, oxygen was not detectable, except for a surface layer of 0.25 mm and in apparent small air pockets within the cheese containing about 3% saturated oxygen.

Cheese↗
PubMed2002

Use of PCR-based methods and PFGE for typing and monitoring homofermentative lactobacilli during Comté cheese ripening.

This study investigated the genotypic characteristics of selected and wild homofermentative thermophilic lactobacilli strains during ripening of Comté cheeses, made into two cheese plants. Both amplification and restriction analysis of the 16S rRNA gene (PCR-ARDRA) and classical biochemical tests were used to identify isolates. Diversity within homofermentative lactobacilli was not found in their species composition since the same two species Lactobacillus helveticus and L. delbrueckii susbp. lactis were isolated from cheeses. In cheeses made with natural whey starter, it appeared that the most likely sources of L. helveticus and L. delbrueckii susbp. lactis were the starter and raw milk, respectively. The examination of RAPD profiles of lactobacilli strains revealed 19 RAPD groups among 50 isolates, which were different from selected starter strains. Using RAPD, REP-PCR, and PFGE to identify selected starter strains during cheese ripening, we showed that L. helveticus decreased quickly while L. delbrueckii susbp. lactis sustained high viability during ripening. The use of selected L. delbrueckii susbp. lactis strains diminished the genetic diversity among strains isolated from cheese, probably in preventing the raw milk microflora from growing.

Bacterial Typing Techniques↗
PubMed1997

Identification and characterization of proteolytic activity of Enterococcus spp. isolated from milk and Roncal and Idiazábal cheese.

Roncal and Idiazábal cheeses are manufactured from ewe's milk in the Autonomous Region of Navarre in Spain. Levels of enterococci are high in these cheeses and in other types of ewe's-milk cheeses. The present study has identified enterococci present in the milk used and in the Roncal and Idiazábal cheeses after 120 days of ripening. A total of 282 strains were isolated and identified, and the cytoplasmic and extracellular enzymatic activities of some of the strains were assessed. The dominating species were Enterococcus faecalis, which accounted for 85% of the total both in the milk as well as in the two types of cheese, and Enterococcus faecium, Enterococcus durans, and Enterococcus avium which were present in lower proportions. Aminopeptidase and proteinase activity levels in enterococci were low, and considerable variation between strains of the same species was recorded, highlighting the need to study individual strains when selecting the most suitable bacteria as a starter culture. Aminopeptidase activity levels for the enterococci were appreciably higher at pH 7 than at pH 5.5, hence aminopeptidase activity by enterococci would appear to be less significant in the normal manufacturing conditions of the two cheeses.

Aminopeptidases↗
PubMed1998

Protection by fungal starters against growth and secondary metabolite production of fungal spoilers of cheese.

The influence of fungal starter cultures on growth and secondary metabolite production of fungal contaminants associated with cheese was studied on laboratory media and Camembert cheese. Isolates of the species Penicillium nalgiovense, P. camemberti, P. roqueforti and Geotrichum candidum were used as fungal starters. The species P. commune, P. caseifulvum, P. verrucosum, P. discolor, P. solitum, P. coprophilum and Aspergillus versicolor were selected as contaminants. The fungal starters showed different competitive ability on laboratory media and Camembert cheese. The presence of the Penicillium species, especially P. nalgiovense, showed an inhibitory effect on the growth of the fungal contaminants on laboratory media. G. candidum caused a significant inhibition of the fungal contaminants on Camembert cheese. The results indicate that G. candidum plays an important role in competition with undesirable microorganisms in mould fermented cheeses. Among the starters, P. nalgiovense caused the largest reduction in secondary metabolite production of the fungal contaminants on the laboratory medium. On Camembert cheese no significant changes in metabolite production of the fungal contaminants was observed in the presence of the starters.

Aflatoxins↗