9-24: Sweetgum bark (Liquidambar styraciflua L.): saccharification and co-product extraction

Sweetgum trees grow freely in Southeastern U.S. and are often considered a nuisance to the lumber industry. They often grow in pine forests and must be removed before the pine trees can be harvested. To make use of this otherwise wasted biomass, sweetgum could be converted into cellulosic ethanol through dilute acid pretreatment, enzymatic hydrolysis, and fermentation. If value added compounds can be identified, the value of sweetgum as a potential biofuel-destined feedstock would increase.

The goal of this project was to determine if soaking the sweetgum bark in 85°C water prior to dilute acid pretreatment and enzymatic hydrolysis would increase the saccharification, and if the wash waters contained biologically active compounds. Soaking resulted in 20% and 5% increases in xylose and glucose recoveries compared to non-soaked bark. These extracts were tested for antioxidant properties. Sweetgum bark yielded 1.7 mg g^-1 of shikimic acid. Extracts also contained gallic acid, which is a documented antioxidant.  Gallic acid reference standard and the sweetgum bark extract were further analyzed for antioxidant effects using the in-vitro Cu²⁺ induced low density lipoprotein oxidation (LDL) thiobarbituric reactive substance (TBARS) assay. Sweetgum bark extract, 12.5 mg ml^-1, and gallic acid, 75 µM, inhibited LDL oxidation by 90%. These results indicated that bark extracts contain compounds, including gallic acid, that display potent antioxidant effects. In addition to recovering phytochemicals, the 85°C wash step also increases xylose recovery. These results demonstrate the possibility of devising a biorefinery operation that could produce biobased fuels and high value phytochemicals from feedstock.