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

Authors

  • Tomáš Brányik,

    Corresponding author
    1. Centro de Engenharia Biológica, Universidade do Minho, Campus de Gualtar, 4710–057 Braga, Portugal
    2. Institute of Chemical Process Fundamentals, Academy of Sciences, Rozvojová 135, 165 02 Prague 6, Czech Republic
    3. Institute of Chemical Technology, Department of Fermentation Chemistry and Bioengineering, Technická 5, 166 28, Prague 6, Czech Republic
    • Centro de Engenharia Biológica, Universidade do Minho, Campus de Gualtar, 4710–057 Braga, Portugal. Ph: +351 253 604406. Fax: +351 253 678986
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  • António A. Vicente,

    1. Centro de Engenharia Biológica, Universidade do Minho, Campus de Gualtar, 4710–057 Braga, Portugal
    2. Institute of Chemical Process Fundamentals, Academy of Sciences, Rozvojová 135, 165 02 Prague 6, Czech Republic
    3. Institute of Chemical Technology, Department of Fermentation Chemistry and Bioengineering, Technická 5, 166 28, Prague 6, Czech Republic
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  • Gabriela Kuncová,

    1. Centro de Engenharia Biológica, Universidade do Minho, Campus de Gualtar, 4710–057 Braga, Portugal
    2. Institute of Chemical Process Fundamentals, Academy of Sciences, Rozvojová 135, 165 02 Prague 6, Czech Republic
    3. Institute of Chemical Technology, Department of Fermentation Chemistry and Bioengineering, Technická 5, 166 28, Prague 6, Czech Republic
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  • Ondřej Podrazký,

    Corresponding author
    1. Centro de Engenharia Biológica, Universidade do Minho, Campus de Gualtar, 4710–057 Braga, Portugal
    2. Institute of Chemical Process Fundamentals, Academy of Sciences, Rozvojová 135, 165 02 Prague 6, Czech Republic
    3. Institute of Chemical Technology, Department of Fermentation Chemistry and Bioengineering, Technická 5, 166 28, Prague 6, Czech Republic
    • Centro de Engenharia Biológica, Universidade do Minho, Campus de Gualtar, 4710–057 Braga, Portugal. Ph: +351 253 604406. Fax: +351 253 678986
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  • Pavel Dostálek,

    1. Centro de Engenharia Biológica, Universidade do Minho, Campus de Gualtar, 4710–057 Braga, Portugal
    2. Institute of Chemical Process Fundamentals, Academy of Sciences, Rozvojová 135, 165 02 Prague 6, Czech Republic
    3. Institute of Chemical Technology, Department of Fermentation Chemistry and Bioengineering, Technická 5, 166 28, Prague 6, Czech Republic
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  • José A. Teixeira

    Corresponding author
    1. Centro de Engenharia Biológica, Universidade do Minho, Campus de Gualtar, 4710–057 Braga, Portugal
    2. Institute of Chemical Process Fundamentals, Academy of Sciences, Rozvojová 135, 165 02 Prague 6, Czech Republic
    3. Institute of Chemical Technology, Department of Fermentation Chemistry and Bioengineering, Technická 5, 166 28, Prague 6, Czech Republic
    • Centro de Engenharia Biológica, Universidade do Minho, Campus de Gualtar, 4710–057 Braga, Portugal. Ph: +351 253 604406. Fax: +351 253 678986
    Search for more papers by this author

Abstract

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 ( qim) 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 (Xactim) of the total immobilized biomass ( Xim) was subsequently estimated at approximately Xactim = 0.12 gIB gC−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 (Xactim) and the maximum attainable biomass load (Xmaxim) was included into the model. Since the average biofilm thickness was estimated at ca. 10 μm, 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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