Researchers Identify Structural Mechanism of Hot Water Pretreatment of Corn Stover for Cellulosic Ethanol Production
|A magnified image of a cornstalk particle shows the many tiny pores that pretreatment opens up. Click to enlarge.|
Researchers at Purdue University have discovered that particles from cornstalks undergo structural changes when processed to produce ethanol, an insight they said will help establish a viable method for large-scale production of cellulosic ethanol.
Their research demonstrates that pretreating corn plant tissue with hot water—an accepted practice that increases ethanol yields 3 to 4 times—works by exposing minute pores of the plant’s cell walls, thus increasing surface area for additional reactions that help break down the cell wall. The work is published in the current edition of the journal Biotechnology and Bioengineering.
Plant cell walls are rigid structures made up of a variety of polymers, including cellulose and hemicellulose, which can be converted into sugars that are then made into ethanol. However, cellulose and hemicellulose are held in place by a variety of compounds like lignin, a strong cellular glue that resists treatment and protects cellulose from being broken down.
Using high-resolution imaging and chemical analyses, the researchers determined that pretreatment opens reactive areas within the cells of the corn stover that were previously overlooked. In the next step of processing, these enlarged pores are more easily accessed by enzymes that convert cellulose into glucose for subsequent fermentation into ethanol.
The researchers found that after pretreatment opens corn’s tiny pores, enzymes not only removed more cellulose and hemicellulose from the cell wall, but also removed it at a faster rate.
The smaller 53-75 micrometer corn stover particles are 1.5X more susceptible to hydrolysis than 425-710 micrometer corn stover particles. This difference between the two particle size ranges is eliminated when the stover is pretreated with liquid hot water pretreatment at 190 degrees C for 15 min, at pH between 4.3 and 6.2. This pretreatment causes ultrastructural changes and formation of micron-sized pores that make the cellulose more accessible to hydrolytic enzymes.
The hot liquid water pretreatment process used in the study was originally developed in the Laboratory of Renewable Resources Engineering at Purdue. The study was funded by the US Department of Energy, US Department of Agriculture and Purdue Agriculture.
“Microscopic Examination of Changes of Plant Cell Structure in Corn Stover Due to Hot Water Pretreatment and Enzymatic Hydrolysis”; Meijuan Zeng, Nathan S. Mosier, Chia-Ping Huang, Debra M. Sherman, Michael R. Ladisch; Biotechnology and Bioengineering Volume 97, Issue 2 , Pages 265 - 278