The new technique uses plant-derived enzyme cocktails to break down orange peels and other waste materials into sugar, which is then fermented into ethanol. The findings are detailed in Plant Biotechnology.
Researchers cloned genes from wood-rotting fungi or bacteria and produced enzymes in tobacco plants. Producing these enzymes in tobacco instead of manufacturing synthetic versions could reduce the cost of production by a thousand times, which should significantly reduce the cost of making ethanol.
Tobacco was chosen as an ideal system for enzyme production because it is not a food crop, produces large amounts of energy per acre and (Of course!) an alternate use could potentially decrease its use for smoking.
Depending on the waste product used, a specific combination or "cocktail" of more than 10 enzymes is needed to change the biomass into sugar and eventually ethanol. Orange peels need more of the pectinase enzyme, while wood waste requires more of the xylanase enzyme. All of the enzymes the team uses are found in nature, created by a range of microbial species, including bacteria and fungi.
Corn starch is currently fermented and converted into ethanol. But ethanol derived from corn produces more greenhouse gas emissions than gasoline does. Ethanol created using the approach produces much lower greenhouse gas emissions than gasoline or electricity.
There's also an abundance of waste products that could be used without reducing the world's food supply or driving up food prices. In Florida alone, discarded orange peels could create about 200 million gallons of ethanol each year.
Citation: Verma et al., 'Chloroplast-derived enzyme cocktails hydrolyse lignocellulosic biomass and release fermentable sugars', Plant Biotechnology, January 2010; doi: 10.1111/j.1467-7652.2009.00486.x
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