Graciele Viccini

Agronomy, Microbiology, Mycology

11.31

Publications

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    ABSTRACT: In solid-state fermentation systems, the growth of aerial hyphae into the interparticle spaces increases the pressure drop through forcefully aerated beds. Aerial hyphae can also bind particles into agglomerates. restricting the transfer of O(2) to the particle surfaces. Despite these important effects, to date relatively little effort has been made to understand the growth patterns of these hyphae. In the current work we present a discrete lattice-based model that can be used to simulate the growth of the aerial hyphae of filamentous fungi. In the model, the elongation of hyphae involves the successive addition of 10 mu m cubes, with random numbers being used to choose the direction of growth. The model was able to describe profiles available in the literature for the density of the aerial hyphae, as a function of height above the surface, for a situation in which the filamentous fungus Rhizopus oligosporus was grown on potato dextrose agar. The model can be modified to describe various different situations involving the growth of filamentous fungi in solid-state fermentation systems, such as the growth of penetrative hyphae and the growth of hyphae within the wet mycelial layer that often forms at the surfaces of particles. It therefore represents a useful tool for investigating phenomena that occur at the micro-scale in solid-state fermentation systems. (C) 2011 Elsevier B.V. All rights reserved.
    Biochemical Engineering Journal 05/2011; 54(3-3):164-171. DOI:10.1016/j.bej.2011.02.012 · 2.37 Impact Factor
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 06/2010; 33(25). DOI:10.1002/chin.200225269
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    ABSTRACT: We describe the purification and chemical characterization of galactomannans that appear both in the biomass and the culture broth during surface-liquid culture of the fungus Clonostachys rosea, a common facultative saprophyte that has potential to be used as a biological control agent against several plant pathogenic fungi, insects and nematodes. The galactomannans from both sources had comparable ratios of Man, Gal and Glc and the similarity were confirmed by (1)H, (13)C NMR, HMQC, and COSY spectra. We propose that the galactomannan in the culture broth originates from autolysis of the biomass, based not only on the similarity that it has with the galactomannan extracted from the biomass but also on the fact that its concentration increased rapidly after glucose depletion from the medium, when biomass concentration was falling. Polysaccharides from C. rosea have not previously been characterized; we show that the characteristics of the galactomannans are consistent with those that have been reported for other members of the Bionectriaceae, the family to which C. rosea belongs.
    Archives of Microbiology 03/2009; 191(4):369-78. DOI:10.1007/s00203-009-0464-0 · 1.86 Impact Factor
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    ABSTRACT: Gray mold caused by Botrytis cinerea is an important disease of strawberry. Clonostachys rosea is a mycoparasite of B. cinerea that reduces fruit losses when used as a biocontrol agent. Since spore production by C. rosea has not been optimized, we investigated factors affecting sporulation under aseptic conditions on white rice grains. The greatest spore production in glass flasks, 3.4 × 109 spores/g-dry-matter (gDM), occurred with an initial moisture content of 46% (w/w wet basis), inoculated with 1 × 106 spores/gDM and hand shaken every 15 days. However, a lower inoculum density (9 × 103 spores/gDM) and no shaking also gave acceptable sporulation. In plastic bags 1.1 × 108 spores/gDM were produced in 15 days, suggesting that larger scale production may be feasible: with this spore content, 24 m2 of incubator space would produce sufficient spores for the continued treatment of 1 ha of strawberry plants.
    PROCESS BIOCHEMISTRY 02/2007; DOI:10.1016/j.procbio.2006.07.006 · 2.52 Impact Factor
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    ABSTRACT: We present a model for the kinetics of microbial growth that incorporates the influence of the temperature variations that typically occur during solid-state culture in large-scale bioreactors. The model proposes that the specific growth rate constant depends on the level of an essential component within the biomass, with the rate of the synthesis and denaturation reactions of this component depending on temperature according to the Arrhenius equation. Model predictions were compared to literature data for the growth of Rhizopus oligosporus in three different situations: (1) incubation of cultures at different but constant temperatures; (2) initial incubation of cultures at 37 °C, followed by incubation at 50 °C; and (3) tray culture. The model agreed reasonably with all three sets of experimental results with the use a single set of parameter values. This approach to modeling has good potential for application in models of solid-state culture bioreactors.
    PROCESS BIOCHEMISTRY 02/2005; 40(2-40):801-807. DOI:10.1016/j.procbio.2004.02.007 · 2.52 Impact Factor
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    Graciele Viccini
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    ABSTRACT: Orientador : David Alexander Mitchell Dissertaçăo (mestrado) - Universidade Federal do Paraná, Setor de Cięncias Biológicas, Programa de Pós-Graduaçăo em Bioquímica. Defesa: Curitiba, 2004 Inclui bibliografia
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    G. Viccini · D. A. Mitchell · N. Krieger
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    ABSTRACT: A mathematical model is developed for converting between the two measurement bases commonly used in the construction of growth profiles in solid-state fermentation, namely absolute mass ratio m(dry biomass)/m (initial dry matter) and relative mass ratio m(dry biomass)/m(dry matter). These are not equivalent, due to the loss of dry matter as CO2 during the fermentation. The model is equally applicable to any biomass component used in indirect measurements of growth, such as protein. Use of the model to convert absolute mass ratio of the biomass profiles for the growth of Rhizopus oligosporus to a relative basis gave profiles that agreed well with the experimentally determined relative biomass profiles. This agreement was obtained for three different fermentations using the same set of parameter values in the model, namely a yield coefficient of m(protein)/m(dry substrate) = 0.2 g/g and a maintenance coefficient of zero, giving confidence in the reliability of the model. The model was then used to show that the measurement basis used can affect the form of the curve and therefore can also affect the conclusion drawn about the type of kinetics shown by the organism, with the extent of this effect depending on the length of time that growth occurs and the values of the yield and maintenance coefficients. This work shows that great care must be taken in drawing conclusions about growth kinetics in solid-state fermentation.
    Food Technology and Biotechnology 01/2003; 41(3):191-201. · 0.98 Impact Factor
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    ABSTRACT: Currently, mathematical models that propose to describe the performance of solid state fermentation bioreactors use simple empirical equations to describe the growth kinetics. However, a systematic analysis of the growth profiles in solid state fermentation systems has not previously been undertaken. In the present work various empirical equations, including the linear, exponential and logistic equations, were fitted to profiles obtained from the literature. The logistic equation gave an adequate description of the whole growth profile in the majority of cases, although in many cases the description is not perfect, with systematic deviations from the best fitting logistic curve, especially decreases in biomass concentration in the later stages of the fermentation and over- or underestimation of the initial biomass concentration by the fitted curve. Clearly, although the logistic equation is commonly used in mathematical models of bioreactor performance, it cannot be treated as though it is a universally applicable equation in solid state fermentation systems. Various improvements that will be necessary before empirical growth equations become truly useful are identified and discussed.
    Food Technology and Biotechnology 10/2001; 39(4-4):271-294. · 0.98 Impact Factor
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    Graciele Viccini

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