Development of t_<50> and its application to evaluate very-high-gravity ethanol fermentation(BIOCHEMICAL ENGINEERING)

概要

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A three-parameter logistic growth model was modified to monitor the glucose uptake profile of yeast during very-high-gravity (VHG) ethanol fermentation. The modified model was used to define t_<50> as a quantifier to differentiate among various fermentation conditions. There are two types of t_<50>; t^g_<50> is the time required to convert 50% of the initial glucose, and t^e_<50> is the time required to produce half of the final ethanol. A 2^4 factorial experimental design was implemented to illustrate the applicability of using t_<50> to isolate active ingredients in VHG growth media. The analytical results obtained from the experimental design and from a modified model were compared, which demonstrated that t_<50> could serve the proposed objectives. A shorter t_<50> implies a faster fermentation. A tailing of the ethanol profile after t^e_<50> indicates that there is an inhibitory effect imposed on yeast, i.e., the stronger the tailing in the ethanol profile, the stronger the inhibitory effect. When t_<50> is equal to or near to the halftime of the total course of the fermentation, a bell-shaped curve was seen for the glucose uptake rate or for the ethanol production rate, indicating that the inhibitory effect exerted on yeast was evenly distributed.