Growing corn is not the answer to our gasoline addiction, but is switchgrass, Miscanthus, or Poplar trees? And if they are, when do we harvest them to get the optimal solutions? Good questions-glad you asked. Because researchers at the U.S. Department of Energy's Ames Laboratory are looking at ways to determine what type of plant material, and specific times of harvest offer a better long-term solution.
Analytical chemist Emily Smith has devised a test based on Raman spectroscopy that can quickly determine the chemical composition of the plant in question. Understanding the composition of the cellulose material is just as important for biofuels as is understanding when a fruit is ripe to pick for eating. Except we did not evolve any specific sense to tell us when poplar trees make for good biofuels. Which is why we need people like Emily.
"Just like vintners monitor and test the sugar content of their grapes in the field, biofuel producers could potentially use this technology to determine if their crop was at optimal development for conversion to ethanol," said Smith. Agriculture has often been spurred by just such screening technologies, and new types of crops will require new thinking when it comes to screening.
"This method has several advantages over other analytical techniques...analysis requires very little material so you can take small samples from a growing plant over time without damaging the plant."
Optimizing plant biomass for more efficient biofuels processing requires a solid understanding of plant cell-wall structure and function. Plant cell walls contain four different polymer types - cellulose microfibrils, hemicelluloses, pectins, and lignins. Lignins are of particular interest as they are not readily turned into ethanol, and can even cause problems in enzymatic breakdown for use of the biomass. Lignin acts like the glue in plant material, holding together other components. One way around this problem is to identify which plants have little lignin or when these plants are lignin deficient.
"We hope to find out if lignin content changes over time, with different growing conditions, or with different stock material," Smith said, "so we can determine if there is an optimal time to harvest a particular crop."
One way to begin to look for sustainable crops might be to take Emily's method for a test drive, and see what plants have interesting lignin properties in your neck of the woods.