A method for the on-line calculation of conversion rates and yield coeffici
ents under dynamic process conditions was developed. The method is based on
cumulated mass balances using a moving average method. Elemental balances
were used to test the measured cumulated quantities for gross errors and in
appropriate stoichiometry definition followed by data reconciliation and es
timation of non-measured conversion rates, using a bioprocess set-up includ
ing multiple on-line analysis techniques. The quantitative potential of the
proposed method is demonstrated by executing transient experiments in aero
bic cultures of Saccharomyces cerevisiae on glucose. Rates and yield coeffi
cients could be consistently quantified in shift-up, shift-down, and accele
rostat experiments. The method shows the capability to describe quantitativ
ely transient changes in metabolism including uncoupling of catabolism and
anabolism, also for the case when multiple components of metabolism are not
measured. The validity of the experiment can be evaluated on-line. Additio
nally, the method detects with high sensitivity inappropriate stoichiometry
definition, such as a change in state of metabolism. It was shown that con
centration values can be misleading for the identification of the metabolic
state. In contrast, the proposed method provides a clear picture of the me
tabolic state and new physiological regulations could be revealed. Hence, t
he novelty of the proposed method is the on-line availability of consistent
stoichiometric coefficients allowing a significant speed up in strain char
acterization and bioprocess development using minimal knowledge of the meta
bolism. Additionally, it opens up the use of transient experiments for phys
iological studies. (C) 2001 John Wiley & Sons, Inc.