Development of t(50) and its application to evaluate very-high-gravity ethanol fermentation

Area of Science:

• Biotechnology
• Fermentation Science
• Yeast Metabolism

Background:

• Very-high-gravity (VHG) ethanol fermentation presents unique challenges for yeast.
• Monitoring glucose uptake and ethanol production is crucial for optimizing VHG processes.
• Existing models may not adequately capture the dynamics of VHG fermentation.

Purpose of the Study:

• To modify a logistic growth model for monitoring yeast glucose uptake in VHG ethanol fermentation.
• To introduce t(50) as a novel quantifier for differentiating fermentation conditions.
• To assess the utility of t(50) in identifying inhibitory effects and active ingredients in VHG media.

Main Methods:

• Modification of a three-parameter logistic growth model.
• Definition and application of two t(50) parameters: t(50)(g) (50% glucose conversion) and t(50)(e) (50% final ethanol production).
• Implementation of a 2(4) factorial experimental design to test the model's applicability.

Main Results:

• The modified model successfully used t(50) to differentiate fermentation conditions.
• A shorter t(50) correlated with faster fermentation rates.
• Ethanol profile 'tailing' after t(50)(e) served as an indicator of yeast inhibitory effects, with stronger tailing signifying stronger inhibition.
• A bell-shaped glucose/ethanol production rate curve was observed when t(50) approached the fermentation halftime, suggesting evenly distributed inhibition.

Conclusions:

• The modified logistic growth model and the t(50) quantifier are effective tools for analyzing VHG ethanol fermentation.
• t(50) provides valuable insights into fermentation speed and the presence/strength of inhibitory factors.
• The model aids in understanding yeast behavior and optimizing VHG fermentation media composition.