PhD defence: Chia-wen Carmen Hsieh

Chia-wen Carmen Hsieh defends her PhD thesis:
Water availability as a measure of cellulose hydrolysis efficiency

Principal supervisor

Senior Researcher Lisbeth Garbrecht Thygesen, Department of Geosciences and Natural Resource Management, Faculty of Science, University of Copenhagen, DK

Co-supervisor

Professor Claus Felby, Department of Geosciences and Natural Resource Management, Faculty of Science, University of Copenhagen, DK

Assessment Committee

Associate professor Anders Blennow, Department of Plant and Enviromental Sciences, Faculty of Science University of Copenhagen, DK

Associate professor  Emma Master, University of Toronto, Canada

Professor Peter Westh, Roskilde University, Roskilde, DK

Summary

Enzymatic hydrolysis involves the use of cellulases to break down cellulose in the presence of water. Therefore, not only are enzyme and substrate properties important for efficient hydrolysis, but also the hydrolysis medium, i.e. the liquid phase. The LF-NMR technique is used in this work to measure properties of the liquid phase, where water protons are characterized based on their mobility in the system as measured by their relaxation time.

Studies of cellulose hydrolysis at low dry matter show that the contents of the liquid phase influence the final hydrolysis yield, as the presence of sugars, salts, and surfactants impact the water relaxation time. Systems with high concentrations of sugars and salts tend to have low water availability, as these form strong interactions with water to keep their solubility, leaving less water available for hydrolysis. Thus, cellulase performance decreases. However, the addition of surfactants such as polyethylene glycol (PEG) increases the water mobility, leading to higher water availability, and ultimately higher glucose production. More specifically, the higher water availability boosts the activity of processive cellulases.

Thus, water availability is vital for efficient hydrolysis, especially at high dry matter content where water availability is low. At high dry matter content, cellulase activity changes water interactions with biomass, affecting the water mobility. While swelling and fiber loosening also take place during hydrolysis, the cellulase hydrolytic activity changes the substrate to give a unique relaxation time profile. In extreme conditions where water is only present as bound water, cellulases are still able to utilize bound water for hydrolysis.

After the PhD defence there will be a reception at Rolighedsvej 23, in the meeting room Skoven, 2^nd floor in the new building. All are welcome.