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Title: Recognition of phase transition in fermentation using on-line monitored variables
Author: Dehghani, Mitra
ISNI:       0000 0001 3421 4726
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 1996
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The aim of this research was to develop a technique by which aerobic batch stirred tank fermenters, containing the yeast S. cerevisiae (strain GB4918, Bakers yeast) cultured in a chemically defined and/or undefined medium with glucose as the initial limiting substrate at 30 g/L, pH 4.5 and temperature 28°C, as well as in repeated fill and draw batch bioreactors, can be controlled and operated by the use of a single on-line parameter that identifies and represents the complex biochemistry of the aerobic yeast and enables the batch cycle to be initiated and terminated, as well as the harvesting of intracellular enzymes of the yeast at optimum yield or concentration. An extensive literature survey has been carried out into the aerobic culture of the yeast S.cerevisiae that identified key transition phases in the metabolism in relation to the operation of cellular metabolic pathways, (limited respiratory capacity, dioxic growth on ethanol). Distinct changes in some of the on-line monitored variables of dissolved oxygen tension (DOT) and CO2 exit gas concentration have been used to recognise the specific identifiable phases of glucose depletion, biomass formation and production of some intracellular enzymes, which in this project were alcohol dehydrogenase (ADH), glucose-6-phosphate dehydrogenase (G6PDH), malate dehydrogenase (MDH), and hexokinase. Direct information about the metabolic activity of the cells and product concentration inside the batch bioreactor were obtained from the off-line samples taken from the culture broth. These on-line and off-line variables were correlated to enable process decision making to be based on calculated parameters rather than using a predetermined schedule. An extensive data base has been set up from the experimentation in terms of the functioning of the yeast cells that gives the change in the external culture environment and the intracellular enzymes associated with glucose metabolism in an aerobic environment. These date place some considerable doubt on the published theories of the cell metabolic functioning. The use of on-line CO2 exit gas data has been clearly demonstrated as a means of assessing and regulating the operation of not only an experimental batch bioreactor, but also provides a reproducible and consistent means of controlling a commercial batch bioreactor.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Yeast fermentation; Bakers yeast; Bioreactor