Abstract
BackgroundA glucose concentration is an important factor for a fed-batch process of Saccharomyces cerevisiae. Therefore, it is necessary to be controlled under a critical concentration to avoid overflow metabolism and to gain high productivity of biomass. In the study, 2D fluorescence spectroscopy was applied for an online monitoring and controlling of the yeast cultivations to attain the pure oxidative metabolism.ResultsThe characteristic of the NADH intensity can effectively identify the metabolic switch between oxidative and oxidoreductive states. Consequently, the feed rate was regulated using the single signal based on the fluorescence intensity of NADH. With this closed-loop control of the glucose concentration, a biomass yield was obtained at 0.5 gbiomass/gglucose. In addition, ethanol production could be avoided during the controlled feeding phase.ConclusionsThe fluorescence sensor with a single signal of the NADH fluorescence intensity has potential to control a glucose concentration under the critical value in real time. Therefore, this achievement of the feedback control is promising to build up a compact and economical fluorescence sensor with the specific wavelength using light-emitting diodes and photodiodes. The sensor could be advantageous to the bioprocess monitoring because of a cost-effective and miniaturized device for routine analysis.
Highlights
A glucose concentration is an important factor for a fed-batch process of Saccharomyces cerevisiae
When the glucose concentration in a yeast cultivation is above a critical value, it leads to oxidoreductive metabolism and ethanol is produced as an overflow metabolite under an aerobic condition (Walker 1998)
Investigation of fluorescence signals corresponding to the metabolic change The biogenic fluorophores, which were examined during the fed-batch process, are the peak intensity in NADH, tryptophan, flavins, and pyridoxine regions
Summary
A glucose concentration is an important factor for a fed-batch process of Saccharomyces cerevisiae. It is necessary to be controlled under a critical concentration to avoid overflow metabolism and to gain high productivity of biomass. The main factor, which is considered in the fed-batch cultivation, is a glucose concentration, because it plays a pivotal role in regulating yeast metabolism. When the glucose concentration in a yeast cultivation is above a critical value, it leads to oxidoreductive metabolism and ethanol is produced as an overflow metabolite under an aerobic condition (Walker 1998). Due to the ethanol production, the yeast cultivation gains a lower biomass yield (Pham et al 1998). This phenomenon has been known as the Crabtree effect caused by a limited respiratory capacity
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