SuGanit ferments xylose using brewer's yeast

By Ryan C. Christiansen | February 04, 2009
SuGanit Systems Inc. in Reston, Va., was awarded a $999,900 grant from the Ohio Department of Development's Third Frontier Advanced Energy Program to scale up its biomass pretreatment and fermentation processes that can ferment both glucose and xylose sugars using normal yeast. SuGanit Systems operates a research and development center at the University of Toledo's Clean & Alternative Energy Incubator in Toledo, Ohio.

According to SuGanit President Praveen Paripati, the company licensed two technologies from the university and has been working with researchers at the College of Engineering to scale up the processes. "The first technology is a pretreatment process based on ionic liquid pretreatment," he said. "It helps to soften or change the cellulose biomass structure to make it a lot more amenable for the enzymes to do their hydrolysis. The other technology ferments xylose sugars, which are five-carbon sugars, using normal yeast. The technology we have licensed [allows us to] get higher productivity."

According to the university, its scientists developed the catalyst that allows unmodified, native yeast to ferment both sugars, which depending on the biomass could increase ethanol production by 30 percent or more. The research is being led by Sasidhar Varanasi, professor of chemical and environmental engineering.

According to Varanasi, baker's or brewer's yeast (Saccharomyces cerevisiae) can readily convert into ethanol the glucose that is recovered from the 40 percent to 50 percent cellulose portion of lignocellulose. However, the common yeast isn't able to ferment xylose, which is obtained through the hydrolysis of the 25 percent to 35 percent hemicellulosic portion of lignocellulose. The common yeast can only ferment xylose if it has first been converted to xylulose, an isomer of xylose in which the atomic particles have been rearranged. The enzyme xylose isomerase can be used to convert xylose to xylulose in a neutral-to-basic solution, but an acidic solution is necessary for fermenting xylulose to ethanol. To overcome this challenge, Varanasi and his team developed a method for converting xylose to xylulose using immobilized enzyme pellets, which contain multiple enzymes, suspended in a neutral-to-basic solution. The method sustains both neutral-to-basic and acidic microenvironments within a single vessel, allowing for the simultaneous conversion of xylose to xylulose and the fermentation of the xylulose to ethanol. Borax is used in the solution to assist with the conversion of xylose to xylulose.

Up to this point, SuGanit has been able to use the processes to convert one kilogram (2.2 pounds) of biomass per day into 0.25 kilograms (0.55 pounds) of ethanol per day using a batch process. The funding will help SuGanit work toward processing 60 kilograms (132 pounds) of biomass to produce five gallons of ethanol per day using a continuous process.

The grant is contingent upon approval from the state Controlling Board. In 2008, SuGanit received a $500,000 grant from the U.S. DOE and a $250,000 grant from the Ohio Third Frontier Advanced Energy Program. The project began with a $100,000 Small Business Innovation Research grant from the U.S. Small Business Administration.