 |
 |
Michael Penner
Associate Professor, Food Science & Technology
|
 |
||||||||||||||
RESEARCH:
Research in my laboratory concerns the conversion of lignocellulosic biomass to value added products, primarily ethanol. Our work involves studies related to the structural properties of lignified plant cell walls and the enzymology associated with hydrolysis of insoluble plant cell wall polysaccharides. The structural studies are aimed at identifying the primary physicochemical properties, including putative crosslinks between cell-wall polymers, relative crystallinity of cell-wall polysaccharides and enzyme accessible surface area, which effect the susceptibility of lignocellulosics to enzymatic degradation. The enzymology done in our laboratory focuses on enzyme adsorption and catalysis, phenomena relevant to soluble enzyme/insoluble substrate systems in general. The ultimate goal of the enzyme studies is to develop a mechanistic model, with associated thermodynamic and kinetic rate constants, consistent with the kinetics of the full-time course of cellulose saccharification.
The general scheme for the production of ethanol is provided below. We are currently working on three aspects of this conversion process. First, we are conducting studies on the optimization of the dilute acid pretreatment of milled biomass. We are using woody and herbaceous feedstocks as primary substrates. The aim of this work is to develop a unifying kinetic model for high temperature/dilute acid pretreatments which accounts for hemicellulose hydrolysis, sugar decomposition reactions and changes in the enzymatic susceptibility of biomass cellulose. Second, we are interested in elucidating the mechanism of action of cellulolytic enzymes. Current studies in our lab focus on the cellulase enzyme system of the fungus Trichoderma reesei. Our model systems include either single enzymes or multiple enzyme complexes catalyzing the hydrolysis of purified microcrystalline cellulose and/or the cellulose component of pretreated biomass. These enzyme systems are representative of the general class of heterogeneous soluble enzyme-insoluble substrate systems which are ubiquitous in nature. Our enzyme studies are aimed at isolating and understanding the two processes common to this type of heterogeneous system: enzyme adsorption to the substrate and the catalytic event. The third area in the biomass conversion scheme in which we are currently active is in the fermentation of the hydrolysate liquid (glucose stream) and the prehydrolysate liquid (xylose stream). In this phase of our research we focus on the optimization of a simultaneous saccharification and fermentation process in which the enzymatic saccharification of cellulose is accomplished concurrently with yeast fermentation. These studies involve the identification and characterization of the physi cochemical properties of the substrate which dictate rates of glucose production and fermentation. Further studies in this area focus on the identification of sugar and lignin degradation products in the prehydrolysate liquid which inhibit fermentation.