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| 2. |
- Björnberg, Anna, et al.
(author)
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Inhibition of the growth of grain-storage molds in vitro by the yeast Pichia anomala (Hansen) Kurtzman
- 1993
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In: Canadian journal of microbiology (Print). - Montreal, Canada : Canadian Science Publishing. - 0008-4166 .- 1480-3275. ; 39:6, s. 623-628
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Journal article (peer-reviewed)abstract
- The potential Use Of yeasts to control grain-storage molds was evaluated by coculturing the yeast Pichia anomala with Penicillium roqueforti and Aspergillus candidus on agar plates, using different temperatures, water activities (a(w)), and nutrient concentrations. Addition of 10 ppm cycloheximide to malt-extract agar inhibited Pichia anomala completely without affecting mold growth, making it possible to quantify the inhibition as a reduction in colony-forming units (cfu). For A. candidus, numbers of cfu and hyphal lengths were reduced at an initial yeast concentration of 10(4) cells/plate and reduced below detection limit at 10(8) cells/plate. A clear reduction in growth of Penicillium roqueforti was only observed at 10(8) yeast cells/plate. The antagonistic effect was generally more pronounced at low (6, 15-degrees-C) and high (30, 37-degrees-C) temperatures than at ambient ones. Pichia anomala inhibited growth of both molds more strongly in a substrate-rich medium than in a medium with a low substrate content. In water agar (low substrate concentration) the degree of inhibition of Penicillium roqueforti was larger at 0.96 a(w) than at 0.98 a(w).
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| 3. |
- 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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| 4. |
- Börjesson, T., et al.
(author)
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Adsorption of volatile fungal metabolites to wheat grains and subsequent desorption
- 1994
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In: Cereal Chemistry. - : American Association of Cereal Chemists. - 0009-0352 .- 1943-3638. ; 71:1, s. 16-20
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Journal article (peer-reviewed)abstract
- Adsorption of the volatile fungal metabolites 2-methylfuran, 3-methyl-1-butanol, and 1-octen-3-ol to wheat grains, and their subsequent desorption, were investigated. Adsorption was performed both dynamically and statically. In the dynamic system, volatile compounds in a N2 flow were led through 400 g of wheat in a glass column. In the static system, 400 g of wheat was stored in an airtight glass vessel containing the volatile compounds in the atmosphere. Three desorption procedures were compared: an N2 flow at 20-degrees-C, an N2 flow at 50-degrees-C, and extraction with supercritical CO2. 3-Methyl-1-butanol and 1-octen-3-ol were efficiently adsorbed and could also readily be desorbed to considerably higher extents at 50-degrees-C than at 20-degrees-C. The supercritical CO2 extraction was more efficient than N2 desorption in extracting volatile compounds, but because of the smaller sample sizes (1 g), the amounts extracted per gram of grain were lower than the amounts extracted with N2 desorption at 50-degrees-C. The adsorbed amount of each volatile compound was calculated as the difference between content in the N2 stream before passage through the wheat and its content after passage. Desorption by means of a N2 stream led to the recovery of about 5% of 2-methylfuran, 35% of 3-methyl-1-butanol, and 100% of 1-octen-3-ol.
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| 5. |
- 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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| 6. |
- Börjesson, Thomas, et al.
(author)
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Volatile Metabolites and Other Indicators of Penicillium aurantiogriseum Growth on Different Substrates
- 1990
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In: Applied and Environmental Microbiology. - Washington : American Society for Microbiology. - 0099-2240 .- 1098-5336. ; 56:12, s. 3705-3710
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Journal article (peer-reviewed)abstract
- Penicillium aurantiogriseum Dierckx was cultivated on six agar substrates (barley meal agar, oat meal agar, wheat meal agar, malt extract agar, Czapek agar, and Norkrans agar) and on oat grain for 5 days in cultivation vessels provided with an inlet and an outlet for air. Volatile metabolites produced by the cultures were collected on a porous polymer adsorbent by passing an airstream through the vessel. Volatile metabolites were collected between days 2 and 5 after inoculation. CO2 production was simultaneously measured, and after the cultivation period ergosterol contents and the numbers of CFU of the cultures were determined. Alcohols of low molecular weight and sesquiterpenes were the dominant compounds found. During growth on oat grain the production of 8-carbon alcohols and 3-methyl-1-butanol was higher and the production of terpenes was lower than during growth on agar substrates. The compositions of the volatile metabolites from oat grain were more similar to those from wheat grain, which was used as a substrate in a previous investigation, than to those produced on any of the agar substrates. Regarding the agar substrates, the production of terpenes was most pronounced on the artificial substrates (Czapek agar and Norkrans agar) whereas alcohol production was highest on substrates based on cereals. The production of volatile metabolites was highly correlated with the production of CO2 and moderately correlated with ergosterol contents, whereas no correlation with the numbers of CFU was found. Thus, the volatile metabolites formed and the ergosterol contents of fungal cultures should be good indicators of present and past fungal activity.
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| 7. |
- Frändberg, Emma, et al.
(author)
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Chitinolytic properties of Bacillus pabuli K1
- 1994
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In: Journal of Applied Bacteriology. - : Wiley-Blackwell. - 0021-8847. ; 76:4, s. 361-367
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Journal article (peer-reviewed)abstract
- The chitinolytic properties of Bacillus pabuli KI isolated from mouldy grain was studied. Chitinase activity was measured as the release of p-nitrophenol from p-nitrophenyl-N,N'-diacetylchitobiose. Influences of substrate concentration and different environmental variables on growth and chitinase activity were determined. The optimum environmental conditions for chitinase production were: 30 degrees C, initial pH 8, initial oxygen 10% and a(w) > 0.99. Chitinase production was induced when B. pabuli KI was grown on colloidal chitin. The smallest chito-oligosaccharide able to induce chitinase production was N,N'-diacetylchitobiose, (GlcNAc)(2). Production was also induced by (GlcNAc)(3) and (GlcNAc)(4). When the bacterium was grown on glucose or N-acetylglucosamine, no chitinases were formed. The highest chitinase production observed was obtained with colloidal chitin as substrate. The production of chitinases by B. pabuli K1 growing on chitin was repressed by high levels (0.6%) of glucose. The production was also repressed by 0.6% starch, laminarin and beta-glucan from barley and by glycerol. The addition of pectin and carboxymethyl cellulose increased chitinase production.
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| 8. |
- Frändberg, Emma, et al.
(author)
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Evaluation of a chromogenic chito-oligosaccharide analogue, p-nitrophenyl-β-D-N,N'-diacetylchitobiose, for the measurement of the chitinolytic activity of bacteria
- 1994
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In: Journal of Applied Bacteriology. - : Wiley-Blackwell. - 0021-8847. ; 76:3, s. 259-263
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Journal article (peer-reviewed)abstract
- Three methods of quantifying chitinase activity were compared. The activities of crude chitinases of 10 bacterial isolates from different environments were estimated in terms of(l) the release of p-nitrophenol from the chromogenic chito-oligosaccharide analogues, p-nitrophenyl-beta-D-N,N'-diacetylchitobiose, p-nitrophenyl-N-acetyl-beta-D-glucosamine and p-nitrophenyl-beta-D-N,N',N''-triacetylchitotriose, (2) the release of reducing sugars from chitin and (3) the formation of clearing zones on chitin agar. When crude chitinase from Bacillus pabuli was used the hydrolysis of p-nitrophenyl-beta-D-N,N'-diacetylchitobiose correlated well with the release of reducing sugars from chitin and the formation of clearing zones on chitin agar. However, when the activity of crude chitinases from the different bacterial isolates were compared no agreement was found between the hydrolysis of p-nitrophenyl-beta-D-N,N'-diacetylchitobiose and the release of reducing sugars from chitin or the formation of clearing zones on chitin agar. It was concluded that the assay with chromogenic p-nitrophenyl chito-oligosaccharide analogues is not well suited for studies that compare the chitinase activity of different bacteria.
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| 9. |
- Krantz-Rülcker, C., et al.
(author)
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Interactions between a soil fungus, Trichoderma harzianum, and IIb metals—adsorption to mycelium and production of complexing metabolites
- 1993
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In: Biometals. - : Springer. - 0966-0844 .- 1572-8773. ; 6:4, s. 223-230
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Journal article (peer-reviewed)abstract
- Fungi are capable of accumulating metals and, in soil, such accumulation may influence metal speciation and transport. The interactions between a common soil fungus, Trichoderma harzianum, and IIb elements were studied in the present investigation. The accumulation of the metals zinc, cadmium and mercury by starved and non-starved mycelium at different pH was determined by a batch technique using radioactive tracers; uptake of the metals was found to be large, with respective distribution coefficients of about 10(3.5), 10(2.5) and 10(4.0) for zinc, cadmium and mercury, respectively. Metal accumulation by a starved system was largely independent of pH in the range 3-9, where in a non-starved system an increased accumulation of zinc (at 10(-8) m) was observed at low pH (3-5). Potentiometric titrations performed on the two systems revealed significant differences in acid capacities, i.e. values close to zero for the starved system and 500-800 meq kg-1 for the non-starved system. The maximum metal uptake was at least 50 mmol kg-1 at pH 6.5 (calculated from adsorption isotherms). The present findings suggests that in the non-starved system a metabolite is produced and then released when the pH is within a certain range.
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| 10. |
- Regnér, S., et al.
(author)
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Ergosterol content in relation to grain kernel weight
- 1994
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In: Cereal Chemistry. - : American Association of Cereal Chemists. - 0009-0352 .- 1943-3638. ; 71:1, s. 55-58
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Journal article (peer-reviewed)abstract
- The relation between fungal biomass content and grain kernel weight was investigated in five lots of grain: three wheat, one rye, and one triticale. Fungal biomass was quantified as ergosterol content. Samples were fractionated on the basis of grain kernel weight using an automatic sorter. In all lots, ergosterol concentrations increased as kernel weight decreased. In four of the five lots, the absolute amount of ergosterol per kernel also increased with decreasing kernel weight. Within-cultivar variation in ergosterol levels could not be explained solely by differences in surface-to-volume ratio. Ergosterol concentrations in the impurities (material not classified as whole, sound kernels) were generally several times higher than those in the original lots. Although concentrations of ergosterol were relatively high in small kernels and impurities, removal of these fractions did not significantly influence the average ergosterol levels of the lots, due to the low relative weight of these fractions. Separation during handling of the grain might, however, lead to extreme ergosterol concentrations in certain locations of the storage bins. These locations can serve as potential starting points for mold growth.
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