The Experts below are selected from a list of 225 Experts worldwide ranked by ideXlab platform
Ailsa D Hocking - One of the best experts on this subject based on the ideXlab platform.
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Effect of reduced water activity and reduced matric potential on the germination of xerophilic and non-xerophilic fungi
International journal of food microbiology, 2010Co-Authors: Yang Huang, Belinda Chapman, Mariam Begum, Ailsa D HockingAbstract:Abstract Reduction in water activity (aw) is used as a microbiological hurdle to prevent food spoilage. To minimize the levels of salt and sugar, which are commonly used to reduce aw, the potential of food structure as a microbiological hurdle needs to be assessed. The concept of matric potential (Ψm) is used to measure the effect of food structure on water movement. This study reports the effect of reduced aw and reduced Ψm on the germination of xerophilic fungi (represented by Eurotium herbariorum) and non-xerophilic fungi (represented by Aspergillus niger) on model glycerol agar media. Germination curves were plotted with the percentage of germinated spores against time. The germination time (tG), which is defined as the time at which 50% of the total viable spores have germinated, was estimated using the Gompertz model. Total viable spores was defined as those spores that were able to germinate under the optimum aw and Ψm conditions for each species, i.e. 0.95 aw and 2.5% agar for E. herbariorum and 0.98 aw and 2.5% agar for A. niger. As aw decreased from 0.90 to 0.85 aw, tG increased significantly for both the xerophilic fungi and non-xerophilic species at equivalent matric potential values. When matric potential was reduced from −12 kPa (2.5% agar) to −38 kPa (12.5% agar), tG of A. niger was significantly extended at 0.90 aw; however, tG remained the same for A. niger at 0.85 aw, and for E. herbariorum at 0.80, 0.85 and 0.90 aw. This study demonstrated that the germination time for non-xerophilic and xerophilic fungi was extended by reduced aw, however the effect of reduced Ψm was limited.
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evaluation of the efficacy of four weak acids as antifungal preservatives in low acid intermediate moisture model food systems
Food Microbiology, 2010Co-Authors: Yang Huang, Mark Wilson, Belinda Chapman, Ailsa D HockingAbstract:Abstract The potential efficacy of four weak acids as preservatives in low-acid intermediate moisture foods was assessed using a glycerol based agar medium. The minimum inhibitory concentrations (MIC, % wt./wt.) of each acid was determined at two pH values (pH 5.0, pH 6.0) and two aw values (0.85, 0.90) for five food spoilage fungi, Eurotium herbariorum, Eurotium rubrum, Aspergillus niger, Aspergillus flavus and Penicillium roqueforti. Sorbic acid, a preservative commonly used to control fungal growth in low-acid intermediate moisture foods, was included as a reference. The MIC values of the four acids were lower at pH 5.0 than pH 6.0 at equivalent aw values, and lower at 0.85 aw than 0.90 aw at equivalent pH values. By comparison with the MIC values of sorbic acid, those of caprylic acid and dehydroacetic acid were generally lower, whereas those for caproic acid were generally higher. No general observation could be made in the case of capric acid. The antifungal activities of all five weak acids appeared related not only to the undissociated form, but also the dissociated form, of each acid.
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Effect of agar concentration on the matric potential of glycerol agar media and the germination and growth of xerophilic and non-xerophilic fungi.
International journal of food microbiology, 2009Co-Authors: Yang Huang, Mark Wilson, Belinda Chapman, Ailsa D HockingAbstract:The concept of water activity (a(w)) does not differentiate between water status resulting from the interaction of water with solutes, and that from interaction of water with matrices, which is termed matric potential (psi(m)). This study reports the effect of agar concentration (1.5, 3.0, 4.5, 6.0, and 7.5%, w/w) on matric potential of glycerol agar media (GA) and the germination and growth of xerophilic fungi (Eurotium herbariorum and E. rubrum) and non-xerophilic fungi (Aspergillus niger, A. flavus, and Penicillium roqueforti) on GA with or without sorbic acid (0.1-0.4%, w/w) at 0.90 a(w) and 0.95 a(w). The matric potential of GA decreased when the agar concentration increased from 1.5 to 7.5%. When the agar concentration increased at each a(w), the radial growth rate of the xerophilic fungi generally increased but the biomass density (biomass per unit area) decreased, whereas the radial growth rate of the non-xerophilic fungi generally decreased but the biomass density was unchanged. In the absence of sorbic acid, the time to germination of each species was similar for all agar concentrations. In the presence of sorbic acid, the time to germination of some species was significantly longer at higher agar concentrations (4.5%-7.5%) than 1.5% agar. This study demonstrated the inhibition effect on germination and growth of non-xerophilic fungi and xerophilic fungi by decreased matric potential resulting from increased agar concentrations, and the different responses of non-xerophilic fungi and xerophilic fungi to water stress from solutes and matrices. The concept of matric potential may be useful in food microbiology to provide a better understanding of fungal growth in complex food matrices.
François Lamarche - One of the best experts on this subject based on the ideXlab platform.
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Effect of inoculation techniques and relative humidity on the growth of molds on the surfaces of yellow layer cakes
Applied and Environmental Microbiology, 1998Co-Authors: Patrick Fustier, Alain Lafond, Claude P. Champagne, François LamarcheAbstract:FOUR INOCULATION TECHNIQUES WERE COMPARED FOR INITIATION OF GROWTH ON CAKE SURFACES: spot, air cabinet, spray (atomizer), and talc addition methods. Molds were isolated from commercial cakes and were identified as Aspergillus sydowii, Aspergillus ochraceus, Penicillium funiculosum, and Eurotium herbariorum. Cake surfaces were inoculated with mold spores and incubated under three equilibrium relative humidity (ERH) levels: 97, 85, and 75%. Random contamination by spores in a ventilated air cabinet was the simplest method of inoculation, but standard deviations in the inoculation rates (20% on a relative scale) were almost twice those observed with the other methods. The spot method was the most reproducible. Cake samples inoculated in the air cabinet had colony counts 10 times lower than those obtained for potato dextrose agar plates at 97% ERH, which was not the case with the spray and talc methods. Growth of molds was much slower in the samples incubated in 75% relative humidity, with all methods. Colony counts were generally similar in systems adjusted at 85 to 97% ERH but were lower for samples incubated at 75% ERH. In comparisons of the shelf life estimates obtained by the various inoculation methods, a correlation coefficient (r) of 0.70 was obtained between the spot method and the other methods of inoculation, while talc, air cabinet, and spray shelf life data were correlated better (r approximately 0.97). The spot method appeared to be the method of choice in consideration of ease of use, precision, and the ability to enable the study of the effects of the environment on mold-free shelf life as well as on the rate of growth of molds on cakes.
Joseph Andrew Clarke - One of the best experts on this subject based on the ideXlab platform.
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Prediction of toxigenic fungal growth in buildings by using a novel modelling system.
Applied and environmental microbiology, 1999Co-Authors: Neil J. Rowan, Cameron Johnstone, R. Craig Mclean, John G. Anderson, Joseph Andrew ClarkeAbstract:In developed countries, people spend a substantial proportion of time indoors, and it is now generally accepted that indoor air quality can have a significant impact on human health (8, 13–15, 18, 22, 27, 41, 50, 52, 53). The indoor environment can contain numerous potentially harmful substances, such as dust mite and cat allergens, formaldehyde, ozone, and volatile organic vapors (1, 28, 38, 42). In the present context, attention is drawn primarily to the presence, growth, and prediction of the xerophilic fungus Eurotium herbariorum and the mycotoxigenic fungi Aspergillus versicolor and Stachybotrys chartarum (15, 20, 22, 27, 34). There is currently a substantial body of evidence to support the view that fungi in buildings can have severe and wide-ranging effects on the general health of occupants (7, 14, 15, 20, 22, 43, 53). Respiratory, allergenic, and other symptoms, including nausea and vomiting, have been diagnosed (14, 15, 18, 22, 43). Several major investigations have concluded that there is a significant correlation between the incidence of high levels of airborne fungal spores containing mycotoxins, particularly from A. versicolor or S. chartarum, and ill health (13–15, 18, 20, 22, 27, 29). For example, in some damp and moldy buildings, airborne concentrations of viable S. chartarum spores containing stachybotryotoxins can reach levels of up to 18,000 CFU/m3 (23). Recent research has focused on the health status of workers in water-damaged office environments after exposure to fungal bioaerosols (13, 28, 42), especially A. versicolor or S. chartarum and their toxigenic metabolites (22, 27). It was concluded that prolonged and intense exposure to these toxigenic fungi is associated with reported disorders of the respiratory and central nervous systems and of the mucous membranes and the cellular and humoral immune system, suggesting a possible immune competency dysfunction (22, 27). Clearly, the prevention of fungal development and mycotoxin production within buildings is a priority. While the use of biocidal compounds may be appropriate to prevent the problem from occurring in new buildings and to alleviate existing problems, it is generally agreed that the preferred strategy is the elimination of conditions which can lead to fungal growth (1, 46). A key element in such a strategy would be a model which could predict the likelihood and extent of toxigenic fungal growth for any given set of conditions (24). Such a model could be used to critically evaluate a building at the design stage for inherent problems, allowing appropriate changes to be made early in the project. It could also be applied to existing problematic buildings to determine the most effective remedial action. Through the International Energy Agency’s Annex 24 program, advanced computer models which can be used to simulate the moisture behavior of structures have been developed (25). However, the main focus of that research has been on the passage of moisture through walls and the prediction of moisture content and condensation within them (25). Until recently, little consideration was given to the prediction of fungal growth within an integrated building simulation model, probably because of the perceived difficulties involved in combining the biological and physical parameters which contribute to the conditions suitable for fungal development. The present interdisciplinary study was undertaken to develop a prototype fungal prediction program for the built environment. First, growth limit curves for the fungi E. herbariorum, A. versicolor, and S. chartarum were mathematically described within a fungal growth prediction (FGP) database. Second, the FGP database was incorporated into the ESP-r environmental modelling system to produce a model that can identify local environmental conditions under which fungal development may occur. Third, the efficacy of the system’s predictive capability was tested by laboratory-based experiments and by comparison of real and simulated data from a building exhibiting visible fungal growth.
Eviatar Nevo - One of the best experts on this subject based on the ideXlab platform.
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A MAPK gene from Dead Sea fungus confers stress tolerance to lithium salt and freezing–thawing: Prospects for saline agriculture
Proceedings of the National Academy of Sciences of the United States of America, 2005Co-Authors: Yan Jin, Song Weining, Eviatar NevoAbstract:The Dead Sea is one of the most saline lakes on earth (≈340 g/liter salinity) and is ≈10 times saltier than the oceans. Eurotium herbariorum, a common fungal species, was isolated from its water. EhHOG gene, encoding a mitogen-activated protein kinase (MAPK) that plays an essential role in the osmoregulatory pathway in yeast and many other eukaryotes, was isolated from E. herbariorum. The deduced amino acid sequences of EhHOG indicated high similarity with homologous genes from Aspergillus nidulans, Saccharomyces cerevisiae, and Schizosaccharomyces pombe and contained a TGY motif for phosphorylation by MAPK kinase. When EhHOG was expressed in S. cerevisiae hog1Δ mutant, the growth and aberrant morphology of hog1Δ mutant was restored under high osmotic stress condition. Moreover, intracellular glycerol content in the transformant increased to a much higher level than that in the mutant during salt-stress situations. hog1Δ mutant complemented by EhHOG outperformed the wild type or had higher genetic fitness under high Li+ and freezing–thawing conditions. The present study revealed the putative presence of a high-osmolarity glycerol response (HOG) pathway in E. herbariorum and the significance of EhHOG in osmotic regulation, heat stress, freeze stress, and oxidative stress. The Dead Sea is becoming increasingly more saline while the fungi living in it evolutionarily adapt to its high-saline environment, particularly with the extraordinarily high Li+ concentration. The Dead Sea is potentially an excellent model for studies of evolution under extreme environments and is an important gene pool for future agricultural genetic engineering prospects.
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Survival of Filamentous Fungi in Hypersaline Dead Sea Water
Microbial Ecology, 2003Co-Authors: Tamar Kis-papo, Aharon Oren, Solomon P. Wasser, Eviatar NevoAbstract:A variety of filamentous fungi have recently been isolated from the Dead Sea (340 g/L total dissolved salts). To assess the extent to which such fungi can survive for prolonged periods in Dead Sea water, we examined the survival of both spores and mycelia in undiluted Dead Sea water and in Dead Sea water diluted to different degrees with distilled water. Mycelia of Aspergillus versicolor and Chaetomium globosum strains isolated from the Dead Sea remained viable for up to 8 weeks in undiluted Dead Sea water. Four Dead Sea isolates (A. versicolor, Eurotium herbariorum, Gymnascella marismortui, and C. globosum) retained their viability in Dead Sea water diluted to 80% during the 12 weeks of the experiment. Mycelia of all species survived for the full term of the experiment in Dead Sea water diluted to 50% and 10% of its original salinity. Comparison of the survival of Dead Sea species and closely related isolates obtained from other locations showed prolonged viability of the strains obtained from the Dead Sea. Spores of isolates obtained from the terrestrial shore of the Dead Sea generally proved less tolerant to suspension in undiluted Dead Sea water than spores of species isolated from the water column. Spores of the species isolated from the control sites had lost their viability in undiluted Dead Sea water within 12 weeks. However, with the exception of Emericella spores, which showed poor survival, a substantial fraction of the spores of Dead Sea fungal isolates remained viable for that period. The difference in survival rate between spores and mycelia of isolates of the same species points to the existence of adapted halotolerant and/or halophilic fungi in the Dead Sea.
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Spatiotemporal diversity of filamentous fungi in the hypersaline Dead Sea
Mycological Research, 2001Co-Authors: Tamar Kis-papo, Isabella Grishkan, Aharon Oren, Solomon P. Wasser, Eviatar NevoAbstract:To investigate the spatial and temporal diversity in the fungal community of the Dead Sea, we collected Dead Sea water samples at eight near-shore localities and at different stations offshore over a 1-year period (1999–2000). In addition, depth profiles were sampled at a deep station (304 m) in the centre of the sea. In the course of the study we obtained 476 isolates, comprising 38 species from 19 genera of Oomycota (1), Zygomycota (2), Ascomycota (13), and mitosporic fungi (3). This brings the total number of species recovered from the Dead Sea to 55. Approximately 43% of the isolates belonged to the genera Aspergillus and Eurotium . Most of the species found appeared only in winter. Fungal diversity increased near the outlets of less saline springs near the shore. The species Aspergillus terreus, A. sydowii, A. versicolor, Eurotium herbariorum, Penicillium westlingii, Cladosporium cladosporoides and C. sphaerospermum were isolated consistently and probably form a stable core of the community. The results suggest that a remarkably diverse fungal diversity may be found in the hypersaline Dead Sea waters. To what extent the fungal diversity recovered was present as dormant spores or as vegetative mycelia remains to be determined.
Yang Huang - One of the best experts on this subject based on the ideXlab platform.
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Effect of reduced water activity and reduced matric potential on the germination of xerophilic and non-xerophilic fungi
International journal of food microbiology, 2010Co-Authors: Yang Huang, Belinda Chapman, Mariam Begum, Ailsa D HockingAbstract:Abstract Reduction in water activity (aw) is used as a microbiological hurdle to prevent food spoilage. To minimize the levels of salt and sugar, which are commonly used to reduce aw, the potential of food structure as a microbiological hurdle needs to be assessed. The concept of matric potential (Ψm) is used to measure the effect of food structure on water movement. This study reports the effect of reduced aw and reduced Ψm on the germination of xerophilic fungi (represented by Eurotium herbariorum) and non-xerophilic fungi (represented by Aspergillus niger) on model glycerol agar media. Germination curves were plotted with the percentage of germinated spores against time. The germination time (tG), which is defined as the time at which 50% of the total viable spores have germinated, was estimated using the Gompertz model. Total viable spores was defined as those spores that were able to germinate under the optimum aw and Ψm conditions for each species, i.e. 0.95 aw and 2.5% agar for E. herbariorum and 0.98 aw and 2.5% agar for A. niger. As aw decreased from 0.90 to 0.85 aw, tG increased significantly for both the xerophilic fungi and non-xerophilic species at equivalent matric potential values. When matric potential was reduced from −12 kPa (2.5% agar) to −38 kPa (12.5% agar), tG of A. niger was significantly extended at 0.90 aw; however, tG remained the same for A. niger at 0.85 aw, and for E. herbariorum at 0.80, 0.85 and 0.90 aw. This study demonstrated that the germination time for non-xerophilic and xerophilic fungi was extended by reduced aw, however the effect of reduced Ψm was limited.
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evaluation of the efficacy of four weak acids as antifungal preservatives in low acid intermediate moisture model food systems
Food Microbiology, 2010Co-Authors: Yang Huang, Mark Wilson, Belinda Chapman, Ailsa D HockingAbstract:Abstract The potential efficacy of four weak acids as preservatives in low-acid intermediate moisture foods was assessed using a glycerol based agar medium. The minimum inhibitory concentrations (MIC, % wt./wt.) of each acid was determined at two pH values (pH 5.0, pH 6.0) and two aw values (0.85, 0.90) for five food spoilage fungi, Eurotium herbariorum, Eurotium rubrum, Aspergillus niger, Aspergillus flavus and Penicillium roqueforti. Sorbic acid, a preservative commonly used to control fungal growth in low-acid intermediate moisture foods, was included as a reference. The MIC values of the four acids were lower at pH 5.0 than pH 6.0 at equivalent aw values, and lower at 0.85 aw than 0.90 aw at equivalent pH values. By comparison with the MIC values of sorbic acid, those of caprylic acid and dehydroacetic acid were generally lower, whereas those for caproic acid were generally higher. No general observation could be made in the case of capric acid. The antifungal activities of all five weak acids appeared related not only to the undissociated form, but also the dissociated form, of each acid.
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Effect of agar concentration on the matric potential of glycerol agar media and the germination and growth of xerophilic and non-xerophilic fungi.
International journal of food microbiology, 2009Co-Authors: Yang Huang, Mark Wilson, Belinda Chapman, Ailsa D HockingAbstract:The concept of water activity (a(w)) does not differentiate between water status resulting from the interaction of water with solutes, and that from interaction of water with matrices, which is termed matric potential (psi(m)). This study reports the effect of agar concentration (1.5, 3.0, 4.5, 6.0, and 7.5%, w/w) on matric potential of glycerol agar media (GA) and the germination and growth of xerophilic fungi (Eurotium herbariorum and E. rubrum) and non-xerophilic fungi (Aspergillus niger, A. flavus, and Penicillium roqueforti) on GA with or without sorbic acid (0.1-0.4%, w/w) at 0.90 a(w) and 0.95 a(w). The matric potential of GA decreased when the agar concentration increased from 1.5 to 7.5%. When the agar concentration increased at each a(w), the radial growth rate of the xerophilic fungi generally increased but the biomass density (biomass per unit area) decreased, whereas the radial growth rate of the non-xerophilic fungi generally decreased but the biomass density was unchanged. In the absence of sorbic acid, the time to germination of each species was similar for all agar concentrations. In the presence of sorbic acid, the time to germination of some species was significantly longer at higher agar concentrations (4.5%-7.5%) than 1.5% agar. This study demonstrated the inhibition effect on germination and growth of non-xerophilic fungi and xerophilic fungi by decreased matric potential resulting from increased agar concentrations, and the different responses of non-xerophilic fungi and xerophilic fungi to water stress from solutes and matrices. The concept of matric potential may be useful in food microbiology to provide a better understanding of fungal growth in complex food matrices.
