Modelling diffusion-reaction phenomena in yeast flocs of Saccharomyces cerevisiae

Vicente, A. A.; Dluhý, M.; Ferreira, E. C.; Teixeira, J. A.

doi:10.1007/pl00008993

Cited by 4 publications

(5 citation statements)

References 26 publications

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“…10 μm. Although the biofilm thickness over the spent grain particles is not homogeneous, the penetration depth of both oxygen and glucose is significantly higher than the estimated maximum average biofilm thickness (35), rendering insignificant the diffusion limitations inside the biofilm. Here, penetration depth is defined as the distance, measured from the surface of the biofilm, corresponding to a volume of cells that are capable of consuming solute (oxygen or glucose) at a rate equal to the solute mass transfer rate at the surface of the biofilm.…”

Section: Discussionmentioning

confidence: 86%

“…Taking into account the determined carrier surface area of 0.38 ± 0.015 m 2 g ‐ 1 , the full biomass loading X max im = 0.62 g IB g C ‐ 1 , the cell water content 70 wt %, the yeast floc density ρ = 1033 kg m ‐ 3 (34), and porosity ϵ = 0.5 (35) adapted for yeast biofilm, it has been possible to estimate the maximum average biofilm thickness at ca. 10 μm.…”

Section: Discussionmentioning

confidence: 99%

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Growth Model and Metabolic Activity of Brewing Yeast Biofilm on the Surface of Spent Grains: A Biocatalyst for Continuous Beer Fermentation

et al. 2004

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In the continuous systems, such as continuous beer fermentation, immobilized cells are kept inside the bioreactor for long periods of time. Thus an important factor in the design and performance of the immobilized yeast reactor is immobilized cell viability and physiology. Both the decreasing specific glucose consumption rate (q(im)) and intracellular redox potential of the cells immobilized to spent grains during continuous cultivation in bubble-column reactor implied alterations in cell physiology. It was hypothesized that the changes of the physiological state of the immobilized brewing yeast were due to the aging process to which the immobilized yeast are exposed in the continuous reactor. The amount of an actively growing fraction (X(im)act) of the total immobilized biomass (X(im)) was subsequently estimated at approximately X(im)act = 0.12 g(IB) g(C)(-1) (IB = dry immobilized biomass, C = dry carrier). A mathematical model of the immobilized yeast biofilm growth on the surface of spent grain particles based on cell deposition (cell-to-carrier adhesion and cell-to-cell attachment), immobilized cell growth, and immobilized biomass detachment (cell outgrowth, biofilm abrasion) was formulated. The concept of the active fraction of immobilized biomass (X(im)act) and the maximum attainable biomass load (X(im)max) was included into the model. Since the average biofilm thickness was estimated at ca. 10 microm, the limitation of the diffusion of substrates inside the yeast biofilm could be neglected. The model successfully predicted the dynamics of the immobilized cell growth, maximum biomass load, free cell growth, and glucose consumption under constant hydrodynamic conditions in a bubble-column reactor. Good agreement between model simulations and experimental data was achieved.

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Section: Discussionmentioning

confidence: 86%

Section: Discussionmentioning

confidence: 99%

Growth Model and Metabolic Activity of Brewing Yeast Biofilm on the Surface of Spent Grains: A Biocatalyst for Continuous Beer Fermentation

et al. 2004

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“…The flocculation of yeast cells is a reversible, asexual and calcium-dependent process in which cells adhere to form flocs consisting of thousands of cells, the use of high cell density systems being investigated and used for separating yeast cells from beer in the brewing industry. In fact, these systems present several advantages as reduced downstream processing costs, reuse of the biomass for extended periods of time, higher productivity, protection against ethanol stress and resistance to contamination by other microorganism [21][22][23][24][25]. Overall, improved efficiency of the SSF will be obtained by using a yeast strain that can work at higher temperatures and has flocculant properties.…”

Section: Introductionmentioning

confidence: 99%

Bioethanol production from hydrothermal pretreated wheat straw by a flocculating Saccharomyces cerevisiae strain – Effect of process conditions

Ruiz

Silva

Ruzene

et al. 2012

Fuel

102

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Wheat straw is nowadays being considered a potential lignocellulose raw material for fuel ethanol production of second generation and as an alternative to conventional fuel ethanol production from cereal crops. In the present study, hydrothermal pretreated wheat straw with high cellulose content (>60%) at 180°C for 30 min was used as substrate in simultaneous saccharification and fermentation (SSF) process for bioethanol production using a thermotolerant flocculating strain of Saccharomyces cerevisiae CA11. In order to evaluate the effects of temperature, substrate concentration (as effective cellulose) and enzyme loading on: (1) ethanol conversion yield, (2) ethanol concentration, and (3) CO 2 concentration a central composite design (CCD) was used. Results showed that the ethanol conversion yield was mainly affected by enzyme loading, whereas for ethanol and CO 2 concentration, enzyme loading and substrate concentration were found to be the most significant parameters. The highest ethanol conversion yield of 85.71% was obtained at 30°C, 2% substrate and 30 FPU of enzyme loading, whereas the maximum ethanol and CO 2 concentrations (14.84 and 14.27 g/L, respectively) were obtained at 45°C, 3% substrate and 30 FPU of enzyme loading, corresponding to an ethanol yield of 82.4%, demonstrating a low enzyme inhibition and a good yeast performance during SSF process. The high cellulose content obtained in hydrothermal pretreatment and the use of a thermotolerant flocculating strain of S. cerevisiae in SSF suggest as a very promising process for bioethanol production.

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“…Based on these results, concentration profiles of glucose and oxygen inside aggregates of S. cerevisiae were simulated and calculations were made for different possible sizes of the yeast flocs, considering also the presence or the absence of a polymeric additive [151] (Fig. 3(a) and (b)).…”

Section: Mass Transfer In Flocculating Cell Culturesmentioning

confidence: 99%

Applications of yeast flocculation in biotechnological processes

Domingues

Vicente

Lima

et al. 2000

Biotechnol. Bioprocess Eng.

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A review on the main aspects associated with yeast flocculation and its application in biotechnological processes is presented. This subject is addressed following three main aspects -the basics of yeast flocculation, the development of "new" flocculating yeast strains and bioreactor development. In what concerns the basics of yeast flocculation, the state of the art on the most relevant aspects of mechanism, physiology and genetics of yeast flocculation is reported. The construction of flocculating yeast strains includes not only the recombinant constitutive flocculent brewer's yeast, but also recombinant flocculent yeast for lactose metabolisation and ethanol production. Furthermore, recent work on the heterologous β-galactosidase production using a recombinant flocculent Saccharomyces cerevisiae is considered. As bioreactors using flocculating yeast cells have particular properties, mainly associated with a high solid phase hold-up, a section dedicated to its operation is presented. Aspects such as bioreactor productivity and culture stability as well as bioreactor hydrodynamics and mass transfer properties of flocculating cell cultures are considered. Finally, the paper concludes describing some of the applications of high cell density flocculation bioreactors and discussing potential new uses of these systems.

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Modelling diffusion-reaction phenomena in yeast flocs of Saccharomyces cerevisiae

Cited by 4 publications

References 26 publications

Growth Model and Metabolic Activity of Brewing Yeast Biofilm on the Surface of Spent Grains: A Biocatalyst for Continuous Beer Fermentation

Growth Model and Metabolic Activity of Brewing Yeast Biofilm on the Surface of Spent Grains: A Biocatalyst for Continuous Beer Fermentation

Bioethanol production from hydrothermal pretreated wheat straw by a flocculating Saccharomyces cerevisiae strain – Effect of process conditions

Applications of yeast flocculation in biotechnological processes

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