| 1. |
- Båth, Klara, et al.
(author)
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Microbiota of an unpasteurised cellar-stored goat cheese from northern Sweden
- 2012
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In: Agricultural and Food Science. - Helsinki, Finland : M T T / Agrifood Research Finland. - 1459-6067 .- 1795-1895. ; 21:2, s. 197-203
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Journal article (peer-reviewed)abstract
- This qualitative study reports on lactic acid bacteria (LAB), yeasts and moulds isolated from three artisanal Swedish cellar-stored goat cheeses aged for 1, 3 and 5 months. Starter culture LAB dominated in the younger cheeses, and Leuconostoc pseudomesenteroides, common in raw goats' milk, had persisted from the unpasteurised milk into all the cheeses. Non-starter LAB dominated in the 5 month cheese, in particular, Lactobacillus sakei, a meat-associated LAB not previously isolated from cheese. Debaryomyces hansenii, and Penicillium and Mucor species were dominant among the yeasts and moulds, respectively. The cheese rind was not formed primarily from Penicillium species as in traditional cheeses such as Camembert - rather, mycelium from Mucor mucedo contributed to rind formation. Mould species known to produce sterigmatocystin, aflatoxins or ochratoxin A in cheese were not isolated in this study; growth of mycotoxigenic Aspergilli may have been inhibited by the cool conditions in the earth-cellar (4-6 degrees C).
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| 2. |
- Feng, X. M., et al.
(author)
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Image analysis for monitoring the barley tempeh fermentation process
- 2007
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In: Journal of Applied Microbiology. - Oxon, United Kingdom : Oxford University Press (OUP). - 1364-5072 .- 1365-2672. ; 103:4, s. 1113-1121
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Journal article (peer-reviewed)abstract
- Aims: To develop a fast, accurate, objective and nondestructive method for monitoring barley tempeh fermentation. Methods and Results: Barley tempeh is a food made from pearled barley grains fermented with Rhizopus oligosporus. Rhizopus oligosporus growth is important for tempeh quality, but quantifying its growth is difficult and laborious. A system was developed for analysing digital images of fermentation stages using two image processing methods. The first employed statistical measures sensitive to image colour and surface structure, and these statistical measures were highly correlated (r = 0.92, n = 75, P < 0.001) with ergosterol content of tempeh fermented with R. oligosporus and lactic acid bacteria (LAB). In the second method, an image-processing algorithm optimized to changes in images of final tempeh products was developed to measure number of visible barley grains. A threshold of 5 visible grains per Petri dish indicated complete tempeh fermentation. When images of tempeh cakes fermented with different inoculation levels of R. oligosporus were analysed the results from the two image processing methods were in good agreement. Conclusion: Image processing proved suitable for monitoring barley tempeh fermentation. The method avoids sampling, is nonintrusive, and only requires a digital camera with good resolution and image analysis software. Significance and Impact of the Study: The system provides a rapid visualization of tempeh product maturation and qualities during fermentation. Automated online monitoring of tempeh fermentation by coupling automated image acquisition with image processing software could be further developed for process control.
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| 3. |
- Leong, Su-lin L., et al.
(author)
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Genome and physiology of the ascomycete filamentous fungus Xeromyces bisporus, the most xerophilic organism isolated to date
- 2015
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In: Environmental Microbiology. - Hoboken, USA : Wiley-Blackwell. - 1462-2912 .- 1462-2920. ; 17:2, s. 496-513
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Journal article (peer-reviewed)abstract
- Xeromyces bisporus can grow on sugary substrates down to 0.61, an extremely low water activity. Its genome size is approximately 22Mb. Gene clusters encoding for secondary metabolites were conspicuously absent; secondary metabolites were not detected experimentally. Thus, in its dry' but nutrient-rich environment, X.bisporus appears to have relinquished abilities for combative interactions. Elements to sense/signal osmotic stress, e.g. HogA pathway, were present in X.bisporus. However, transcriptomes at optimal (approximate to 0.89) versus low a(w) (0.68) revealed differential expression of only a few stress-related genes; among these, certain (not all) steps for glycerol synthesis were upregulated. Xeromyces bisporus increased glycerol production during hypo- and hyper-osmotic stress, and much of its wet weight comprised water and rinsable solutes; leaked solutes may form a protective slime. Xeromyces bisporus and other food-borne moulds increased membrane fatty acid saturation as water activity decreased. Such modifications did not appear to be transcriptionally regulated in X.bisporus; however, genes modulating sterols, phospholipids and the cell wall were differentially expressed. Xeromyces bisporus was previously proposed to be a chaophile', preferring solutes that disorder biomolecular structures. Both X.bisporus and the closely related xerophile, Xerochrysium xerophilum, with low membrane unsaturation indices, could represent a phylogenetic cluster of chaophiles'.
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| 4. |
- Sugunan, Abhilash, et al.
(author)
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Nutrition-Driven Assembly of Colloidal Nanoparticles : Growing fungi assemble gold nanoparticles as microwires
- 2007
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In: Advanced Materials. - Weinheim, Germany : Wiley. - 0935-9648 .- 1521-4095. ; 19:1, s. 77-81
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Journal article (peer-reviewed)abstract
- The use of a living fungus to 'actively' assemble presynthesized gold nano-particles over its hyphae, resulting in conducting microstructures (see figure), is reported. This physiologically (nutrition) driven process of colloidal self-organization avoids the need for sophisticated DNA/protein chemistry for facilitating interfacing with biological surfaces. The obtained gold-laden microstructures can be modified into flat ribbonlike or tubular morphologies by simple post-formation processing.
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| 5. |
- Feng, X. M., et al.
(author)
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Rhizopus oligosporus and yeast co-cultivation during barley tempeh fermentation-Nutritional impact and real-time PCR quantification of fungal growth dynamics
- 2007
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In: Food microbiology (Print). - London, United Kingdom : Elsevier BV. - 0740-0020 .- 1095-9998. ; 24:4, s. 393-402
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Journal article (peer-reviewed)abstract
- Barley tempeh was produced by fermenting barley kernels with Rhizopus oligosporus. The potential of the yeasts Saccharomyces cerevisiae (three strains), S. boulardii (one strain), Pichia anomala (one strain) and Kluyveromyces lactis (one strain) to grow together with R. oligosporus during barley tempeh fermentation was evaluated. All yeast strains grew during the fermentation and even during cold storage of tempeh (P < 0.01). The growth of yeasts slightly increased the ergosterol contents, but did not influence amino acid contents and compositions, and did not reduce phytate contents. Slight increases of vitamins B6 and niacinamide, and slight decreases of B1 and biotin were observed. Quantification of fungal growth is difficult during mixed species fermentations because ergosterol is found in all fungal species, and colony-forming-unit (cfu) estimations are not reliable for R. oligosporus and other sporulating fungi. Therefore, we developed a quantitative real-time PCR method for individually quantifying S. cerevisiae and R. oligosporus growth in barley tempeh. The PCR results were highly correlated with the ergosterol content of R. oligosporus and with the number of cfu of S. cerevisiae. Thus, real-time PCR is a rapid and selective method to quantify yeasts and R. oligosporus during mixed species fermentation of inhomogenous substrate such as barley tempeh. © 2006 Elsevier Ltd. All rights reserved.
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| 6. |
- Blomqvist, Johanna, et al.
(author)
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Fermentation characteristics of Dekkera bruxellensis strains
- 2010
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In: Applied Microbiology and Biotechnology. - New York, USA : Springer. - 0175-7598 .- 1432-0614. ; 87:4, s. 1487-1497
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Journal article (peer-reviewed)abstract
- The influence of pH, temperature and carbon source (glucose and maltose) on growth rate and ethanol yield of Dekkera bruxellensis was investigated using a full-factorial design. Growth rate and ethanol yield were lower on maltose than on glucose. In controlled oxygen-limited batch cultivations, the ethanol yield of the different combinations varied from 0.42 to 0.45 g (g glucose)(-1) and growth rates varied from 0.037 to 0.050 h(-1). The effect of temperature on growth rate and ethanol yield was negligible. It was not possible to model neither growth rate nor ethanol yield from the full-factorial design, as only marginal differences were observed in the conditions tested. When comparing three D. bruxellensis strains and two industrial isolates of Saccharomyces cerevisiae, S. cerevisiae grew five times faster, but the ethanol yields were 0-13% lower. The glycerol yields of S. cerevisiae strains were up to six-fold higher compared to D. bruxellensis, and the biomass yields reached only 72-84% of D. bruxellensis. Our results demonstrate that D. bruxellensis is robust to large changes in pH and temperature and may have a more energy-efficient metabolism under oxygen limitation than S. cerevisiae.
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| 7. |
- Blomqvist, Johanna, et al.
(author)
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Fermentation of lignocellulosic hydrolysate by the alternative industrial ethanol yeast Dekkera bruxellensis
- 2011
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In: Letters in Applied Microbiology. - Malden, USA : Wiley-Blackwell. - 0266-8254 .- 1472-765X. ; 53:1, s. 73-78
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Journal article (peer-reviewed)abstract
- Aim: Testing the ability of the alternative ethanol production yeast Dekkera bruxellensis to produce ethanol from lignocellulose hydrolysate and comparing it to Saccharomyces cerevisiae.Methods and Results: Industrial isolates of D. bruxellensis and S. cerevisiae were cultivated in small-scale batch fermentations of enzymatically hydrolysed steam exploded aspen sawdust. Different dilutions of hydrolysate were tested. None of the yeasts grew in undiluted or 1 : 2 diluted hydrolysate [final glucose concentration always adjusted to 40 g l(-1) (0.22 mol l(-1))]. This was most likely due to the presence of inhibitors such as acetate or furfural. In 1 : 5 hydrolysate, S. cerevisiae grew, but not D. bruxellensis, and in 1 : 10 hydrolysate, both yeasts grew. An external vitamin source (e.g. yeast extract) was essential for growth of D. bruxellensis in this lignocellulosic hydrolysate and strongly stimulated S. cerevisiae growth and ethanol production. Ethanol yields of 0 42 +/- 0 01 g ethanol (g glucose)(-1) were observed for both yeasts in 1 : 10 hydrolysate. In small-scale continuous cultures with cell recirculation, with a gradual increase in the hydrolysate concentration, D. bruxellensis was able to grow in 1 : 5 hydrolysate. In bioreactor experiments with cell recirculation, hydrolysate contents were increased up to 1 : 2 hydrolysate, without significant losses in ethanol yields for both yeasts and only slight differences in viable cell counts, indicating an ability of both yeasts to adapt to toxic compounds in the hydrolysate.Conclusions: Dekkera bruxellensis and S. cerevisiae have a similar potential to ferment lignocellulose hydrolysate to ethanol and to adapt to fermentation inhibitors in the hydrolysate.Significance and Impact of the study: This is the first study investigating the potential of D. bruxellensis to ferment lignocellulosic hydrolysate. Its high competitiveness in industrial fermentations makes D. bruxellensis an interesting alternative for ethanol production from those substrates.
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| 8. |
- Borjesson, T., et al.
(author)
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Volatile metabolites produced by six fungal species compared with other indicators of fungal growth on cereal grains
- 1992
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In: Applied and Environmental Microbiology. - Washington : American Society for Microbiology. - 0099-2240 .- 1098-5336. ; 58:8, s. 2599-2605
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Journal article (peer-reviewed)abstract
- Six fungal species, Penicillium brevicompactum, P. glabrum, P. roqueforti, Aspergillus flavus, A. versicolor, and A. candidus, were inoculated on moistened and autoclaved wheat and oat grains. They were cultivated in glass vessels provided with an inlet and outlet for air. Air was passed through the vessels to collect volatile fungal metabolites on porous polymer adsorbents attached to the outlet. Samples were collected at two fungal growth stages. Adsorbed compounds were thermally desorbed, separated by gas chromatography, and identified by mass spectrometry. Differences in the production of volatile metabolites depended more on the fungal species than on the grain type. The fungal growth stage was not an important factor determining the composition of volatiles produced. 3-Methylfuran was produced in similar amounts regardless of the fungal species and substrate (oat versus wheat). The production of volatile metabolites was compared with the production of ergosterol and CO2 and the number of CFU. The production of volatile metabolites was more strongly correlated with accumulated CO2 production than with actual CO2 production and more strongly correlated with ergosterol contents of the grain than with numbers of CFU.
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| 9. |
- Börjesson, Thomas S., et al.
(author)
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Off-odorous compounds produced by molds on oatmeal agar : Identification and relation to other growth characteristics
- 1993
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In: Journal of Agricultural and Food Chemistry. - Washington : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 41:11, s. 2104-2111
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Journal article (peer-reviewed)abstract
- Ten Penicillium and Aspergillus species, four with a strong musty off-odor and six reference fungi without any characteristic odor, were cultivated on oatmeal agar for 5 days in cultivation vessels provided with an inlet and an outlet for air. Samples of volatile metabolites were collected on a porous polymer adsorbent attached to the outlet from day 2 through day 5 after inoculation. Adsorbed compounds were desorbed thermally and analyzed with GC/MS and a combined GC and sensory analysis, the GC sniff technique. Multivariate analysis of GC/MS and fungal odor data revealed strong associations between 6 of 65 volatile compounds and musty off-odor. The GC sniff technique showed that five of these, dimethyl disulfide, 1-octen-3-ol, 2-methylisoborneol, and two C11H18 compounds, had prominent off-odors. In addition, geosmin, 1-methoxy-3-methylbenzene, and methylphenol were produced in large amounts by some off-odorous fungi and contributed to their unpleasant odor. 3-Methylfuran, 2-methyl-1-propanol, and 3-methyl-1-butanol were much more commonly produced than the off-odorous compounds. Both odorous and other volatile metabolites could be detected after 2 days of fungal growth. The production of odorous metabolites was enhanced at the time of sporulation.
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| 10. |
- Jennessen, Jennifer, et al.
(author)
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Morphological characteristics of sporangiospores of the tempe fungus Rhizopus oligosporus differentiate it from other taxa of the R-microsporus group
- 2008
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In: Mycological Research. - Oxon, United Kingdom : Elsevier BV. - 0953-7562 .- 1469-8102. ; 112, s. 547-563
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Journal article (peer-reviewed)abstract
- The fungus Rhizopus oligosporus (R. microsporus var. oligosporus) is traditionally used to make tempe, a fermented food based on soybeans. Interest in the fungus has steadily increased, as it can also ferment other substrates, produce enzymes, and treat waste material. R. oligosporus belongs to the R. microsporus group consisting of morphologically similar taxa, which are associated with food fermentation, pathogenesis, or unwanted metabolite production (rhizonins and rhizoxins). The ornamentation pattern, shape, and size of sporangiospores of 26 R. microsporus group strains and two R. oryzae strains were studied using low-temperature SEM (LT-SEM) and LM. This study has shown that: (1) LT-SEM generates images from well-conserved sporangiophores, sporangia, and spores. (2) Robust spore ornamentation patterns can be linked to all different taxa of the R. microsporus group, some previously incorrectly characterized as smooth. Ornamentation included valleys and ridges running in parallel, granular plateaus, or smooth polar areas. Distribution of ornamentation patterns was related to spore shape, which either was regular, ranging from globose to ellipsoidal, or irregular. Specific differences in spore shape, size, and ornamentation were observed between Rhizopus taxa, and sometimes between strains. (3) R. oligosporus has a defect in the spore formation process, which may be related to the domesticated nature of this taxon. It had a high proportion, 10-31 %, of large and irregular spores, and was significantly differentiated from other, natural Rhizopus taxa as evaluated with partial least squares discriminant analysis. it is remarkable that the vehicle of distribution, the sporangiospore, is affected in the strains that are distributed by human activity. This provides information about the specificity and speed of changes that occur in fungal strains because of their use in (food) industry.
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