Conditions promoting effective very high gravity sugarcane juice fermentation

Area of Science:

• Biotechnology
• Fermentation Science
• Bioenergy

Background:

• Very high gravity (VHG) fermentation of sugarcane juice (SCJ) can enhance bioethanol industry sustainability.
• VHG fermentation reduces the need for major infrastructure changes and decreases resource consumption (cane, water, energy).
• This study investigates an industrially relevant SCJ-VHG fermentation process.

Purpose of the Study:

• To demonstrate and characterize an effective, industrially relevant SCJ-VHG fermentation process.
• To investigate the effects of yeast strain and nitrogen source on fermentation performance.
• To analyze glycerol retention and related gene expression under VHG conditions.

Main Methods:

• Utilized an industry-like SCJ-VHG bioethanol production process with 30 and 35 °Bx broths.
• Investigated the impact of different yeast strains (Saccharomyces cerevisiae CAT-1) and nitrogen sources (urea).
• Measured process yield, productivity, biomass viability, glycerol concentration, and gene expression (STL1, FPS1).

Main Results:

• Achieved highest process efficiency with 17% (w/v) ethanol yield and minimal residual sugar (0.2% w/v) using *Saccharomyces cerevisiae* CAT-1 in 30 °Bx broth with urea.
• Efficient glycerol retention by yeast was crucial for fermentation, correlating with higher *STL1* and *FPS1* gene expression.
• Urea supplementation promoted *STL1* expression, overcoming glucose repression, and ethanol secretion may occur via the Fps1 channel.

Conclusions:

• VHG conditions are highly effective for SCJ fermentations, bringing the process closer to industrial application.
• Concentrating SCJ to 30 °Bx, with appropriate nitrogen supplementation and yeast strain, maintains industrially relevant ethanol yields.
• This study enhances understanding of VHG-SCJ process parameters and yeast strain responses for improved efficiency.