Sorghum as a renewable feedstock for production of fuels and industrial chemicals

Considerable efforts have been made in the USA and other countries to develop renewable feedstocks for production of fuels and chemicals. Among these, sorghum has attracted strong interest because of its many good characteristics such as rapid growth and high sugar accumulation, high biomass production potential, excellent nitrogen usage efficiency, wide adaptability, drought resistance, and water lodging tolerance and salinity resistance. The ability to withstand severe drought conditions and its high water usage efficiency make sorghum a good renewable feedstock suitable for cultivation in arid regions, such as the southern US and many areas in Africa and Asia. Sorghum varieties include grain sorghum, sweet sorghum, and biomass sorghum. Grain sorghum, having starch content equivalent to corn, has been considered as a feedstock for ethanol production. Its tannin content, however, may cause problems during enzyme hydrolysis. Sweet sorghum juice contains sucrose, glucose and fructose, which are readily fermentable by Saccharomyces cerevisiae and hence is a good substrate for ethanol fermentation. The enzyme invertase, however, needs to be added to convert sucrose to glucose and fructose if the juice is used for production of industrial chemicals in fermentation processes that employ microorganisms incapable of metabolizing sucrose. Biomass sorghum requires pretreatment prior to enzymatic hydrolysis to generate fermentable sugars to be used in the subsequent fermentation process. This report reviews the current knowledge on bioconversion of sorghum to fuels and chemicals and identifies areas that deserve further studies.