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Simulation of the dynamics in the Baker's yeast process

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Abstract

Simulation of the dynamics in a fed batch process for production of Baker's yeast is discussed and applied. Experimental evidences are presented for a model of the energy metabolism. The model involves the concept of a maximum respiratory capacity of the cell. If the sugar concentration is increased above a critical value, corresponding to a critical rate of glycolysis and a maximum rate of respiration, then all additional sugar consumed at higher sugar concentrations is converted into ethanol.

In a fed batch process with constant sugar feed the sugar concentration declines slowly. If ethanol is present when the sugar concentration declines below the critical value of 110 mg/dm3 fructose +glucose the metabolism switches rapidly into combined oxidation of sugar and ethanol. Thus, no diauxic growth is involved under process conditions. The rate of ethanol consumption is determined by the free capacity of respiration under these conditions. The invertase activity of the cells was found to be so high that mainly fructose and glucose were present in the medium, typically in the concentration range around 100 mg/dm3. These components are consumed at the same rate but with fructose at a higher concentration, indicating a higher K s for fructose consumption.

The model was used in simulation experiments to demonstrate the dynamics of the Baker's yeast process and the influence of different process conditions.

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Abbreviations

DOT % air sat:

dissolved oxygen tension

F dm3/h:

rate of inlet medium flow

H kg/(dm3 % air sat.):

oxygen solubility

K kg/m3 :

saturation constant specified by index

K L a 1/h:

volumetric oxygen transfer coefficient

m g/(g · h):

maintenance coefficient specified by index

P kg/(m3 · h):

mean productivity of biomass in the process

q g/(g · h):

specific consumption or production rate

S kg/m3 :

concentration of sugar in reactor

S 0 kg/m3 :

concentration of inlet medium sugar

t h:

process time

V dm3 :

medium volume

X kg/m3 :

concentration of biomass

Y g/g:

yield coefficient specified by index

μ 1/h:

specific growth rate

aa :

anaerobic condition

c :

critical value

e :

ethanol

ec :

ethanol consumption

ep :

ethanol production

max :

maximum value

o :

oxygen

oe :

oxygen for growth on ethanol

os :

oxygen for growth on sugar

s :

sugar

x :

biomass

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Authors and Affiliations

  1. Department of Biochemistry and Biotechnology, The Royal Institute of Technology, S-10044, Stockholm

    S. -O. Enfors

  2. Svenska Jästfabriks AB, P.O. Box 7003, S-19107, Sollentuna, Sweden

    J. Hedenberg & K. Olsson

Authors
  1. S. -O. Enfors
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  2. J. Hedenberg
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  3. K. Olsson
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Enfors, S.O., Hedenberg, J. & Olsson, K. Simulation of the dynamics in the Baker's yeast process. Bioprocess Engineering 5, 191–198 (1990). https://doi.org/10.1007/BF00376225

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  • DOI: https://doi.org/10.1007/BF00376225

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