Lignocellulosic waste such as sawdust or straw can be used to produce biofuel – but only if the long cellulose and xylan chains can be successfully broken down into smaller sugar molecules.
To do this, fungi are used which, by means of a specific chemical signal, can be made to produce the necessary enzymes.
Because this procedure is, however, very expensive, Vienna University of Technology has been investigating the molecular switch that regulates enzyme production in the fungus. As a result, it is now possible to manufacture genetically modified fungi that produce the necessary enzymes fully independently, thus making biofuel production significantly cheaper.
Biofuel can be obtained quite easily from starchy plants – but this places fuel production in competition with food production. Manufacturing biofuel from lignocellulose is therefore a preferable option.
"Lignocellulose from wood waste or straw is the world's most common renewable raw material but, due to its complex structure, it is significantly more difficult to exploit than starch," explains Prof. Robert Mach from the Institute of Chemical Engineering at Vienna University of Technology.
Biofuel manufacturing uses the Trichoderma fungus, which produces enzymes that are capable of breaking down the cellulose and xylan chains into sugar molecules. The fungus does not, however, always produce these enzymes; production must be stimulated using what is known as an 'inductor' (disaccharide sophorose).
Sophorose as a pure substance currently has a market value of around EUR 2500 per gram – by way of comparison, one gram of gold costs around EUR 40. "The high costs of the chemical inductor are a decisive price driver in biofuel manufacturing," adds Robert Mach.