EFFECTS OF ENZYME LOADING ON EXTRUSION AND ALKALI EXTRUSION PRETREATED SWEET SORGHUM BAGASSE
Matthew Maxwell1, Danielle Bellmer2.
1Southeastern Oklahoma State University, Durant, OK, 2Oklahoma State University, Stillwater, OK.
Biofuels have the potential to mitigate the demand for fossil fuels, reduce the greenhouse gas effect, and greatly expand the market for renewable energy. Sweet sorghum is a promising bioenergy crop due to its high productivity, low input requirements, and versatility. It has tremendous carbohydrate potential if the available starch, cellulose, and hemicellulose can be converted to fermentable sugar in addition to the existing soluble sugars. Extrusion pretreatment using twin-screw extrusion technology has been used on various feedstocks such as switchgrass, corn stover, etc. In addition, alkali soaking in combination with extrusion has been used to help break down lignin in order to better access the cellulose and hemicellulose in lignocellulosic feedstocks. The objective of this experiment was to evaluate the effects of extrusion and alkali extrusion as a pretreatment method for enzymatic hydrolysis of sweet sorghum. A twin-screw extruder was used to pretreat sorghum at 110 °C with and without alkali pretreatment (4% sodium hydroxide). Samples from each pretreatment were subjected to enzymatic hydrolysis of cellulose and starch at a solid loading of 6%. Samples were loaded with 3 different levels of cellulase and xylanase enzymes. Samples were analyzed for carbohydrates using an HPLC. Sugar yields were compared to enzymatic hydrolysis of non-pretreated sorghum samples. Results show that extrusion pretreatment with and without alkali results in increased carbohydrate conversion to sugars compared to untreated samples. As expected, increased enzyme levels resulted in increased sugar yields.