Mycotoxin-forming ability of two Penicillium roqueforti strains in blue moldy tulum cheese ripened at various temperatures

Temperature versus Relative Humidity: Which Is More Important for Indoor Mold Prevention?

Temperature is known as one of the abiotic factors that can affect mold growth. Many mold growth prediction models consider temperature as one of the parameters that can significantly impact mold growth indoors, and hence temperature has been targeted by different indoor mold prevention strategies on different premises. For example, European guidelines for libraries suggest a temperature of 19 °C to preserve books. However, running low temperature air-conditioning (AC) costs substantially more energy, and thus a higher temperature (e.g., 25.5 °C) has been regularly proposed as the recommended indoor temperature for general indoor environments in Hong Kong. It is, therefore, needed to understand whether or not the reduction of indoor temperature would lead to better effectiveness of mold prevention. Using Cladosporium cladosporioides (C. cladosporioides) as the model, its germinating spores were challenged in C. cladosporioides to wet-dry cycles with different combinations of relative humidity (RH, 40%, 60% and 80%) and temperature (19 °C and 28 °C) levels. The survival, lipid peroxidation and catalase (CAT) activity of the treated spores were monitored and compared. C. cladosporioides spores showed similar levels of viability, lipid peroxidation and CAT activity when they were exposed to 19 °C and 28 °C at the same RH, but substantially lower survival and higher oxidative stress were observed under the wet-dry cycles with 40% RH dry periods compared with 60% and 80% RH at both temperatures, suggesting that indoor temperature does not tend to affect the resistance of C. cladosporioides to wet-dry cycles as significantly as the RH level of the dry period. Collectively, this study suggests a more important role for moisture over temperature in indoor mold prevention. The outcome of this study may facilitate the sustainable management of indoor mold problems in buildings.

Tyrosine Induced Metabolome Alterations of Penicillium roqueforti and Quantitation of Secondary Key Metabolites in Blue-Mold Cheese

To map qualitative and quantitative metabolome alterations when Penicillium roqueforti is grown in an environment where l-tyrosine levels are perturbed, the recently established differential off-line LC-NMR (DOLC-NMR) approach was successfully applied in connection with an absolute metabolite quantitation using a quantitative ¹H NMR protocol following the ERETIC 2 (Electronic REference To access In vivo Concentrations) methodology. Among the 23 influenced metabolites, amino acid degradation products like 2-(4-hydroxyphenyl)acetic acid and 2-(3,4-dihydroxyphenyl)acetic acid underwent a tremendous upregulation in the amino acid perturbed approach. Moreover, the output of secondary metabolites like andrastin A, eremofortin B, and the tetrapeptide d-Phe-l-Val-d-Val-l-Tyr was affected in the case of the presence or absence of the added aromatic amino acid. Furthermore, the isolated secondary metabolites of P. roqueforti have been quantified for the first time in five divergent Penicillium isolates by means of a validated LC-ECHO-MS/MS method. This technique is used to compensate the effect of co-extracted matrix compounds during the analysis and to utilize quasi-internal standards to quantify all metabolites of interest accurately. This screening outlined the great variety between the different fungi of the same species. The metabolite spectra of wild-type fungi included more toxic intermediates compared to a selected fungi used as a starter culture for blue-mold cheese production. In addition, these secondary metabolites were quantified in commercially available white- and blue-mold cheese samples. The main differences between the analyte profiles of white and blue cheeses were linked to the impact of the used starter culture. Specific metabolites detected from P. roqueforti like andrastin A and B or roquefortine C could not be detected in white cheese. Among the blue cheese samples, different metabolite pattern could be observed regarding various P. roqueforti starter cultures.

PR Toxin - Biosynthesis, Genetic Regulation, Toxicological Potential, Prevention and Control Measures: Overview and Challenges

Out of the various mycotoxigenic food and feed contaminant, the fungal species belonging to Penicillium genera, particularly Penicillium roqueforti is of great economic importance, and well known for its crucial role in the manufacturing of Roquefort and Gorgonzola cheese. The mycotoxicosis effect of this mold is due to secretion of several metabolites, of which PR toxin is of considerable importance, with regard to food quality and safety challenges issues. The food products and silages enriched with PR toxin could lead into damage to vital internal organs, gastrointestinal perturbations, carcinogenicity, immunotoxicity, necrosis, and enzyme inhibition. Moreover, it also has the significant mutagenic potential to disrupt/alter the crucial processes like DNA replication, transcription, and translation at the molecular level. The high genetic diversities in between the various strains of P. roqueforti persuaded their nominations with Protected Geographical Indication (PGI), accordingly to the cheese type, they have been employed. Recently, the biosynthetic mechanism and toxicogenetic studies unraveled the role of ari1 and prx gene clusters that cross-talk with the synthesis of other metabolites or involve other cross-regulatory pathways to negatively regulate/inhibit the other biosynthetic route targeted for production of a strain-specific metabolites. Interestingly, the chemical conversion that imparts toxic properties to PR toxin is the substitution/oxidation of functional hydroxyl group (-OH) to aldehyde group (-CHO). The rapid conversion of PR toxin to the other derivatives such as PR imine, PR amide, and PR acid, based on conditions available reflects their unstability and degradative aspects. Since the PR toxin-induced toxicity could not be eliminated safely, the assessment of dose-response and other pharmacological aspects for its safe consumption is indispensable. The present review describes the natural occurrences, diversity, biosynthesis, genetics, toxicological aspects, control and prevention strategies, and other management aspects of PR toxin with paying special attention on economic impacts with intended legislations for avoiding PR toxin contamination with respect to food security and other biosafety purposes.

Microflora of processed cheese and the factors affecting it

The basic raw materials for the production of processed cheese are natural cheese which is treated by heat with the addition of emulsifying salts. From a point of view of the melting temperatures used (and the pH-value of the product), the course of processed cheese production can be considered "pasteurisation of cheese." During the melting process, the majority of vegetative forms of microorganisms, including bacteria of the family Enterobacteriaceae, are inactivated. The melting temperatures are not sufficient to kill the endospores, which survive the process but are often weakened. From a microbiological point of view, the biggest contamination problem of processed cheese is caused by gram-positive spore-forming rod-shaped bacteria of the genera Bacillus, Geobacillus, and Clostridium. Other factors affecting the shelf-life and quality of processed cheese are mainly the microbiological quality of the raw materials used, strict hygienic conditions during the manufacturing process as well as the type of packaging materials and storage conditions. The quality of processed cheese is not only dependent on the ingredients used but also on other parameters such as the value of water activity of the processed cheese, its pH-value, the presence of salts and emulsifying salts and the amount of fat in the product.

Modeling Growth and Toxin Production of Toxigenic Fungi Signaled in Cheese under Different Temperature and Water Activity Regimes

The aim of this study was to investigate in vitro and model the effect of temperature (T) and water activity (aw) conditions on growth and toxin production by some toxigenic fungi signaled in cheese. Aspergillus versicolor, Penicillium camemberti, P. citrinum, P. crustosum, P. nalgiovense, P. nordicum, P. roqueforti, P. verrucosum were considered they were grown under different T (0-40 °C) and aw (0.78-0.99) regimes. The highest relative growth occurred around 25 °C; all the fungi were very susceptible to aw and 0.99 was optimal for almost all species (except for A. versicolor, awopt = 0.96). The highest toxin production occurred between 15 and 25 °C and 0.96-0.99 aw. Therefore, during grana cheese ripening, managed between 15 and 22 °C, ochratoxin A (OTA), penitrem A (PA), roquefortine-C (ROQ-C) and mycophenolic acid (MPA) are apparently at the highest production risk. Bete and logistic function described fungal growth under different T and aw regimes well, respectively. Bete function described also STC, PA, ROQ-C and OTA production as well as function of T. These models would be very useful as starting point to develop a mechanistic model to predict fungal growth and toxin production during cheese ripening and to help advising the most proper setting of environmental factors to minimize the contamination risk.

Filamentous Fungi and Mycotoxins in Cheese: A Review

Important fungi growing on cheese include Penicillium, Aspergillus, Cladosporium, Geotrichum, Mucor, and Trichoderma. For some cheeses, such as Camembert, Roquefort, molds are intentionally added. However, some contaminating or technological fungal species have the potential to produce undesirable metabolites such as mycotoxins. The most hazardous mycotoxins found in cheese, ochratoxin A and aflatoxin M1, are produced by unwanted fungal species either via direct cheese contamination or indirect milk contamination (animal feed contamination), respectively. To date, no human food poisoning cases have been associated with contaminated cheese consumption. However, although some studies state that cheese is an unfavorable matrix for mycotoxin production; these metabolites are actually detected in cheeses at various concentrations. In this context, questions can be raised concerning mycotoxin production in cheese, the biotic and abiotic factors influencing their production, mycotoxin relative toxicity as well as the methods used for detection and quantification. This review emphasizes future challenges that need to be addressed by the scientific community, fungal culture manufacturers, and artisanal and industrial cheese producers.

Food fermentations: microorganisms with technological beneficial use

Microbial food cultures have directly or indirectly come under various regulatory frameworks in the course of the last decades. Several of those regulatory frameworks put emphasis on "the history of use", "traditional food", or "general recognition of safety". Authoritative lists of microorganisms with a documented use in food have therefore come into high demand. One such list was published in 2002 as a result of a joint project between the International Dairy Federation (IDF) and the European Food and Feed Cultures Association (EFFCA). The "2002 IDF inventory" has become a de facto reference for food cultures in practical use. However, as the focus mainly was on commercially available dairy cultures, there was an unmet need for a list with a wider scope. We present an updated inventory of microorganisms used in food fermentations covering a wide range of food matrices (dairy, meat, fish, vegetables, legumes, cereals, beverages, and vinegar). We have also reviewed and updated the taxonomy of the microorganisms used in food fermentations in order to bring the taxonomy in agreement with the current standing in nomenclature.

Development of real-time PCR methods to quantify patulin-producing molds in food products

Patulin is a mycotoxin produced by different Penicillium and Aspergillus strains isolated from food products. To improve food safety, the presence of patulin-producing molds in foods should be quantified. In the present work, two real-time (RTi) PCR protocols based on SYBR Green and TaqMan were developed. Thirty four patulin producers and 28 non-producers strains belonging to different species usually reported in food products were used. The patulin production was tested by mycellar electrokinetic capillary electrophoresis (MECE) and high-pressure liquid chromatography-mass spectrometry (HPLC-MS). A primer pair F-idhtrb/R-idhtrb and the probe IDHprobe were designed from the isoepoxydon dehydrogenase (idh) gene, involved in patulin biosynthesis. The functionality of the developed method was demonstrated by the high linear relationship of the standard curves constructed with the idh gene copy number and Ct values for the different patulin producers tested. The ability to quantify patulin producers of the developed SYBR Green and TaqMan assays in artificially inoculated food samples was successful, with a minimum threshold of 10 conidia g(-1) per reaction. The developed methods quantified with high efficiency fungal load in foods. These RTi-PCR protocols, are proposed to be used to quantify patulin-producing molds in food products and to prevent patulin from entering the food chain.

Mycotoxins and mould contamination in cheese: a review

Many types of cheese are an excellent substrate for mould growth. Important fungi growing on cheese include Penicillium, Aspergillus, Cladosporium, Geotrichum, Mucor and Trichoderma. Incidence of moulds in cheese indicates that the predominant flora belong to the genus Penicillium. Some types of cheese such as Camembert and Roquefort cheese intentionally contain moulds. In the production of these kinds of cheeses, starter fungal cultures that have low toxigenic capacity should be selected and spontaneously moulded cheeses should not be consumed to avoid mycotoxin risk. Mycotoxins produced by certain moulds as a toxic metabolic substances can be found in dairy products from two origins: (1) indirect contamination, which results when dairy cows ingest feed that contains mycotoxins that pass into the milk such as aflatoxin M1, and (2) direct contamination, which occurs because of the intentional or accidental growth of moulds. The most common mycotoxins which are stable in cheese are citrinin, penitrem A, roquefortine C, sterigmatocystin and aflatoxin. On the other hand patulin, penicillic acid and PR toxin do not persist in cheese. The significance of patulin, penicillic acid, and mycophenolic acid in cheese in small amounts is probably not great from a public health standpoint because of their low oral toxicity while sterigmatocystin is of more concern because of its carcinogenicity. Mycotoxins may cause fatal poisoning and toxic effects called acute and chronic mycotoxicoses. Several human and animal intoxications by mycotoxins have been reported such as 'turkey's X disease', alimentary toxic aleukia and yellow rain. Mycotoxin production in foods can be affected by temperature, food substrate, strain of mould and other environmental factors. There are physical, chemical and biological methods to prevent the growth of fungi, eliminate or reduce the toxin levels, degrade or detoxify the toxins in foods and feeds. However, the best way for avoiding mycotoxins in dairy products is to prevent mould contamination since there are limitations of degradation or detoxifications.

A practical approach for identifications based on mycotoxin characters of Penicillium

The taxonomy of the penicillia is unstable particularly in the important antibiotic and mycotoxin-producing subgenus Penicillium. There are difficulties relating identifications to mycotoxin production. Also, the validity of dual nomenclature for pleomorphic fungi is under discussion increasingly. Patulin is an important mycotoxin produced by various fungi and has strict limits in the European Union. The mycotoxin and/or the isoepoxydon dehydrogenase (IDH) gene of the metabolic pathway have been assessed in 318 strains predominately of subgenus Penicillium. These data were used to classify the isolates. Subgenus Penicillium contained most of the IDH and patulin positives. The species and varieties in subgenus Penicillium which were associated with patulin detection can be reduced to one name, viz. Penicillium Pen p+ (p = patulin). This has been extended to other mycotoxin producing penicillia to indicate the scope of the scheme. The classification will lead to the number of taxa being reduced, while avoiding species names and hence dual nomenclature. Culture independent analysis of environmental samples is mentioned. The scheme could be used with advantage for other fungi.