Bioprocess Engineering

, Volume 11, Issue 4, pp 135–144

A robust fed-batch feeding strategy for optimal parameter estimation for baker's yeast production

  • A. O. Ejiofor
  • C. H. Posten
  • B. O. Solomon
  • W. -D. Deckwer
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Abstract

Parameter identification of structured models is often a problem in biotechnology, because the poor data situation and the number of unknown parameters only allow for inaccurate estimates. But often only a subset of all kinetic parameters of the model are of interest for production purposes, e.g. for fed-batch cultivation. These parameters should be estimated with a given accuracy. In addition, the experiments for information acquisition with respect to these parameters should be as simple as possible and should consider some practical restrictions. In this contribution a fed-batch feeding strategy is proposed to allow for an accurate estimation of yield and of critical growth rate of baker's yeast. The feeding also allows for economic and stereotyped use of staff and equipment and is therefore suitable for routine use in screening of strains and media. The overall pattern is similar to that one, usually used in production scale to minimize errors by limited model validity. After an initial phase for achieving a reproducible state three different growth rates are adjusted to cover the range of possible critical growth rates. From biomass and ethanol measurements yield and critical growth rate can be estimated with an accuracy of about 2.1%. The fermentation pattern ends up with a constant feeding rate to simulate a limited oxygen transfer rate and to allow for an uptake of residual sugar and ethanol before a dough test can be carried out. Beside experimental results simulations and sensitivity analyses are shown.

List of Symbols

P

ethanol concentration

S

substrate concentration

Sf

substrate concentration in feed

T

fermentation time

V

fermenter volume

X

biomass concentration

C

measurement error covariance matrix

F

Fisher information matrix

X

state variables

Y

output variables

Xp

state sensitivity functions with respect to parameters

Yp

output sensitivity functions

e

eigenvectors

k

vector of limitation and inhibition parameters

n

number of observations

qin

feeding stream

qb

stream for samples and ammonia feed

r

vector of specific turnover rates

y

vector of yields

ρ

specific weight

λ

eigenvalues

μ

specific growth rate

μset

exponent in exponential feeding

σ

standard deviation

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Copyright information

© Springer-Verlag 1994

Authors and Affiliations

  • A. O. Ejiofor
    • 1
  • C. H. Posten
    • 1
  • B. O. Solomon
    • 1
  • W. -D. Deckwer
    • 1
  1. 1.GBF-Gesellschaft für Biotechnologische ForschungBraunschweigGermany
  2. 2.Department of Applied Microbiology & BrewingNnamdi Azikiwe UniversityAwkaNigeria
  3. 3.Department of Chemical EngineeringObafemi Awolowo UniversityIle-IfeNigeria

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