Abstract
Saccharomyces cerevisiae AFY is a novel baker’s yeast strain with strong freeze-tolerance, and can be used for frozen-dough processing. The present study armed to clarify the growth characteristics of the yeast AFY. Aerobic batch culture experiments of yeast AFY were carried out using media with various initial glucose concentrations, and the culture process was analyzed kinetically. The growth of the yeast AFY exhibited a diauxic pattern with the first growth stage consuming glucose and the second growth stage consuming ethanol. The cell yield decreased with increasing initial glucose concentration in the first growth stage, and also decreased with increasing initial ethanol concentration in the second growth stage. In the initial glucose concentration range of 5.0–40.0 g/L, the simultaneous equations of Monod equation, Luedeking–Piret equation and pseudo-Luedeking–Piret equation could be used to describe the concentrations of cell, ethanol and glucose in either of the two exponential growth phases. At the initial glucose concentrations of 5.0, 10.0 and 40.0 g/L, the first exponential growth phase had a maximal specific cell growth rate of 0.52, 0.98 and 0.99 h−1, while the second exponential growth phase had a maximal specific cell growth rate of 0.11, 0.06 and 0.07 h−1, respectively. It was indicated that the efficiency of the yeast production could be improved by reducing the ethanol production in the first growth stage.
Highlights
In the glucose metabolism of yeasts, glucose can be metabolized via two different energy producing pathways, i.e. oxidation or fermentation (Serio et al 2001)
The oxidative metabolism leads to cell growth, while the fermentative metabolism leads to ethanol formation
The reduction of specific cell growth rate in the second growth phase was due to the metabolic difference of glucose and ethanol (Wills 1990), and the changes of nutrient and cell concentrations in the culture broth, etc. These results indicated that the efficiency of yeast production could be improved by reducing ethanol production in the first growth stage
Summary
In the glucose metabolism of yeasts, glucose can be metabolized via two different energy producing pathways, i.e. oxidation or fermentation (Serio et al 2001). The oxidative metabolism leads to cell growth, while the fermentative metabolism leads to ethanol formation. The cell growth or the ethanol formation is mainly determined by the physiological state of yeast, which can be inferred from a suitable metabolic flux balance approach (Barrera-Martínez et al 2011). The cell growth or the ethanol formation is affected by the concentrations of glucose and oxygen in culture media. A high glucose concentration or a low oxygen concentration in culture media may result in the Crabtree effect which inhibits the cell growth and increases the ethanol formation (Win et al 1996; Serio et al 2001).
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