The amount of acid or base consumed in yeast
cultures has been recently assigned to the pathway of
nitrogen assimilation under respiratory conditions with
no contribution by carbon metabolism (Castrillo et al.,
1995). In this investigation, experiments under respirofermentative
conditions have shown that production or
consumption of ethanol does not contribute significantly
to the specific rate of proton production (qH+), thus extending
the previously obtained relationships for all
aerobic conditions in which other major acid/base contributions
are not involved. Tests in batch and chemostat
culture confirm the validity of qH+ as a formal control
parameter in aerobic fermentations.Junta Nacional de Investigação Científica e Tecnológica

Gobierno Vasco (Departamento de Educación, Universidadese Investigación)

Ministerio de Educación y Ciencia-Acciones Integrada

Christensen

Duboc

Fiechter

Gmehling

Grosz

Kharasch

Nielsen

Oeggerli

Rarey

Reid

Royce

Schlauer

Schulze

Stouthamer

Tempest

Thornton

van der Heijden

Verduyn

von Stockar

Wang

Weast

Wilson

Biotechnology and Bioengineering

Abstract: The amount of acid or base consumed in yeast cultures has been recently assigned to the pathway of nitrogen assimilation under respiratory conditions with no contribution by carbon metabolism (Castrillo et al., 1995). In this investigation, experiments under respiro-fermentative conditions have shown that production or consumption of ethanol does not contribute significantly to the specific rate of proton production (qH+), thus ex-tending the previously obtained relationships for all aerobic conditions in which other major acid/base con-tributions are not involved. Tests in batch and chemostat culture confirm the validity of qH+ as a formal control parameter in aerobic fermentations. © 1998 John Wiley &amp

Antonio Vicente

Juan I. Castrillo

Jose ́ A. Teixeira

Unai Ugalde

CiteSeerX

On-line estimation of biomass through pH control analysis in aerobic yeast fermentation systems

The amount of acid or base consumed in yeast
cultures has been recently assigned to the pathway of
nitrogen assimilation under respiratory conditions with
no contribution by carbon metabolism (Castrillo et al.,
1995). In this investigation, experiments under respirofermentative
conditions have shown that production or
consumption of ethanol does not contribute significantly
to the specific rate of proton production (qH+), thus extending
the previously obtained relationships for all
aerobic conditions in which other major acid/base contributions
are not involved. Tests in batch and chemostat
culture confirm the validity of qH+ as a formal control
parameter in aerobic fermentations.Junta Nacional de Investigação Científica e Tecnológica; Gobierno Vasco (Departamento de Educación, Universidade Investigación); Ministerio de Educación y Ciencia-Acciones Integradas

Vicente, A. A.

Castrillo, Juan I.

Teixeira, J. A.

Ugalde, Unai

Universidade do Minho: RepositoriUM

BIOTEC’98 BBE007 207 On-line estimation of biomass through pH control analysis in aerobic yeast fermentation systems  António Vicente1, Juan I. Castrillo2, José A. Teixeira1, Unai Ugalde2,* 1Centro de Engenharia Biológica - IBQF, Universidade do Minho, 4700 Braga, Portugal 2Unidad de Bioquímica, Departamento de Química Aplicada, Facultad de Ciencias Químicas, Universidad del País Vasco, P.O. Box 1072, 20080 San Sebastián, Spain.  Key words: On-line control, pH control, growth monitoring, proton titration, yeast   Biomass determination is a basic parameter in fermentation processes. Therefore, simple and reliable on-line estimation procedures are highly desirable, particularly in fermentation processes using Saccharomyces cerevisiae [1,2], which are widely used in industry. Experimental evidence of the existence of a direct relationship between proton production and growth has been presented in the past [3,4]. The determination of the equivalents of acid or base consumed by the culture per unit time has been a widely used parameter for on-line control processes [5,6]. Nevertheless, the majority of studies have been restricted to the establishment of empirical relations, while the physiological basis of the models proposed remained unclear. Many studies on changes in medium pH associated with growth processes pointed to metabolic activity as the principal cause of medium proton exchange [3,7]. This fact was confirmed in a recent study in which the nitrogen assimilation pathway was certified as the main contributing pathway under aerobic conditions and respiratory metabolism [8]. The aim of this work is to verify the applicability of the model described above to those aerobic conditions in which respiro-fermentative metabolism is involved with production and consumption of ethanol. Experiments have been performed with dilution rates ranging from 0.11 to 0.38 h-1, using urea as the nitrogen source, in order to evaluate the contribution of the fermentative pathway to the total specific rate of proton production or consumption by the culture (qH+, mmol-1 h-1 gbiom-1), determined as in Castrillo and Ugalde [8]. The experiments have shown that production or consumption of ethanol does not contribute significantly to the specific rate of proton production (qH+), thus extending the previously obtained relations [8] for all aerobic conditions in which other major acid/base contributions are not involved. This constitutes the fundamental metabolic basis by which many fermentation processes can be monitored through the accurate titration of the pH control reagent. Those relations may be usefully applied in fermentation control processes as formal rules, extensive for many different microorganisms displaying similar physiological patterns. Tests in batch and chemostat culture confirm the validity of qH+ as a formal control parameter in fermentations.  [1] Fiechter, A., Käppeli, O., Meussdoerffer, F., In: A. H. Rose, and J. S. Harrison (eds.), The yeasts, vol.2, 2nd edition, Academic Press, London, 99-129, 1987. [2] Verduyn, C., Postma, E., Scheffers, W. A., van Dijken, J. P., Yeast, 8, 501-517, 1992. [3] Huth, J., Werner, S., Mueller, H. G., J. Basic Microbiol. 30, 561-567, 1990. [4] Roos, W., Luckner, M.,. J. Gen. Microbiol., 130, 1007-1014, 1984. [5] Ishizaki, A., Tripetchkul, S., Tonokawa, M., Shi, Z. P., Shimizu, K., J. Ferment. Bioeng., 77, 541-547, 1994. [6] San, K.-Y., Stephanopoulos, G., Biotechnol. Bioeng., 26, 1209-1218, 1984. [7] Kotyk, A., In: S. Fleischer, and B. Fleischer (eds.). Methods in Enzymology, vol. 174 (Biomembranes, Part U), Academic Press, New York, 592-603, 1989. [8] Castrillo, J.I., de Miguel, I. and Ugalde, U. O., Yeast, 11, 1353-1365. 1995. 

Systematic errors due to the neglect of water and/or ethanol partition between liq. and gaseous phases are discussed for bioreactors equipped with or without a condenser. Both water vapor and ethanol vapor are present in the off-gas leaving the condenser. Presence of residual water vapor largely influences the gas measurements by diln. As a consequence, the oxygen consumption rate can be overestimated by a factor of 3 if calcns. are not cor. for water vapor content or if no addnl. device is implemented.after the condenser to completely dry the off-gases. The mass balance and partition equations predict that the condenser has only a small effect on redn. of the ethanol vapor content of the off-gas. The reason is the high ethanol concn. of the condensate droplets on the condenser wall in contact with the off-gases. Model predictions as well as exptl. results show that ethanol evapn. represents a large fraction of the ethanol prodn. rate and influences greatly the elemental recoveries. For a reactor working at 30 DegC without condensation of the vapors and for a volumetric aeration rate of 0.63vvm, stripping of ethanol resulted in a gaseous diln. rate of 0.016 h-1 for ethanol. The diln. rate by stripping was reduced to 0.014 h-1 when a condenser at 12 DegC was implemented. The fraction of ethanol that is stripped is mainly dependent on the ratio D/vvm (liq. to gaseous flow rates), and the effect is only slightly influenced by low condenser temp. The evapn. of ethanol may account for more than 20% of the ethanol formation rate. Therefore, the condenser does not succeed to reflux all ethanol to the reactor broth. In terms of a unit operation, ethanol vapor can be efficiently reduced by absorption instead of condensation. To demonstrate the feasibility, a simple modification of the reactor was tested for continuous cultures: the feed port was changed from the top-plate to the top of the condenser, which was used as an absorption column. Ethanol stripping was reduced by a factor of 4 as compared to the condensation setup (at 12 DegC): it accounted for 2% of the ethanol prodn. rate as compared to 8.2% at D = 0.19 h-1 and 0.63vvm. [on SciFinder (R)

Duboc, Philippe

von Stockar, Urs

Infoscience - École polytechnique fédérale de Lausanne

Systematic errors in data evaluation due to ethanol stripping and water vaporization

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http://repositorium.sdum.uminho.pt/bitstream/1822/3892/1/BIOTEC98.BBE007%5b1%5d.pdf

On-line estimation of biomass through pH control analysis in aerobic yeast fermentation systems

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Universidade do Minho: RepositoriUM

Universidade do Minho: RepositoriUM

Universidade do Minho: RepositoriUM

Infoscience - École polytechnique fédérale de Lausanne

Crossref