Year: 1983
Type: article
Abstract: Nutritional and Environmental Factors in Ethanol Fermentation by Saccharomyces cerevisiaeHarry Wong Using Saccharomyces cerevisiae as a model system, a basic study of the nutritional and environmental factors in ethanol fermentation was carried out to provide fundamental and practical bases for design of fermentation media and culture conditions.The requirements for all active medium components need to be determined in order to establish balanced media, which are important to reduce raw materials costs and to minimize inhibition from buildup of excess feed components in recycle processes with selective ethanol removal.Pulse injection of nutrients into continuous cultures was an effective method for screening active nutrients.In a systematic sensitivity analysis the effect of feed concentration of these.individualnutrients was then determined and allowed formulation of media optimal with respect to the major fermentation parameters.Biotin, pantothenate, myo-inositol, potassium and phosphates appeared to stimulate growth preferentially to ethanol production.In contrast, thiamine and pyridoxine appeared to enhance specific ethanol productivity.The effect of ammonium sulfate depended on concentration.A conceptual model was proposed to relate the effects of these nutrients to biochemical pathways and functions.With these data and model the minimum cost combination of raw materials to achieve a medium of well defined components can be determined with a linear program.This computer program shows that many growth factors and minerals can be added to media more economically as pure components than as fractions of complex factors.The effect of dissolved oxygen was studied from essentially zero to 346 mmHg oxygen tension, showing a continuous decline in specific ethanol productivity with increasing oxygen over this range.Oxygen uptake rates under fermentative conditions showed approximately saturation kinetics as a function of dissolved oxygen tension for varying dilution rates.This fermentative oxygen demand of order 30 mg 0 2 /g dry cells was related to requirements for biosynthesis of unsaturated fatty acids and ergosterol.The internal cell reaction rate for o 2 appeared, to control the rate of o 2 uptake, which appeared to be by passive diffusion.Long term continuous cultures resulted in decreased media requirements for growth factors and increased tolerance for ethanol inhibition, most probably through adaptation.An ethanol productivity of 5.6 g/L-hr in continuous culture was achieved with a completely synthetic medium with the improved culture.Specific media requirements for a process need to be determined with the actual organism, raw materials and environmental conditions to be used.Many of the trends observed in this study should, nevertheless, be applicable to organisms with similar metabolism.
Authors: Hee‐Kit Wong, C. R. Wilke, Harvey W. Blanch
Language: English
Subfield: Biomedical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W92662579