Production of fermentable sugars from corn fiber using soaking in aqueous ammonia (saa) pretreatment and fermentation to succinic acid by Escherichia coli afp184

Authors: YOO, CHANG GEUN - Oak Ridge National Laboratory; Nghiem, Nhuan; KIM, TAE HYUN - Kongiu National University

Submitted to: Korean Journal of Chemical Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2016
Publication Date: 9/1/2016
Publication URL: http://handle.nal.usda.gov/10113/63278
Citation: Yoo, C., Nghiem, N.P., Kim, T. 2016. Production of fermentable sugars from corn fiber using soaking in aqueous ammonia (saa) pretreatment and fermentation to succinic acid by Escherichia coli afp184. Korean Journal of Chemical Engineering. 33(10):2863-2868.

Interpretive Summary: Corn fiber is a low-value co-product in a corn processing plant using the wet-milling process. Corn fiber contains significant amounts of carbohydrates, and therefore, is a potential source of sugars that can be used for production of additional ethanol and industrial chemicals in fermentation processes. In the present investigation a bio/chemical processing scheme was developed for production of fermentable sugars from corn fiber. The developed process included pretreatment of corn fiber with aqueous ammonia to render the cellulosic components more accessible to enzyme action, which released glucose, a readily fermentable six-carbon sugar, and an acid treatment, which released xylose and arabinose, the major five-carbon sugars. The fermentability of the sugar solution was demonstrated with a microorganism capable of producing succinic acid at high rates and yields. Succinic acid was chosen for this study because it is a feedstock for production of many important industrial chemicals and consumer products.

Technical Abstract: Conversion of corn fiber (CF), a by-product from the corn-to-ethanol conversion process, into fermentable sugar and succinic acid was investigated using soaking in aqueous ammonia (SAA) pretreatment followed by biological conversions including enzymatic hydrolysis and fermentation using genetically engineered E. coli (AFP184). The SAA pretreatment (using a 15% w/w NH4OH solution at a solid-to-liquid ratio of 1:10 at 60 degree C for 24 h) removed 20-38% of lignin and significantly improved the digestibility of the treated solid (85 – 99% of glucan digestibility). Following the enzymatic hydrolysis, the sugar-rich hydrolysate was subjected to dilute sulfuric acid treatment (1 wt.% sulfuric acid and 120 degree C for 1 h), which hydrolyzed the oligosaccharides in the hydrolysate into fermentable monomeric sugars. The mixed sugar hydrolysates containing hexose and pentose obtained from the two-step hydrolysis and SAA pretreatment were fermented to succinic acid using a genetically engineered microorganism, Escherichia coli AFP184, for evaluating the fermentability. Engineered E. coli AFP184 effectively converted soluble sugars in the hydrolysate to succinic acid (20.7 g/L), and the production rate and yield were further enhanced with additional nutrients; the highest concentration of succinic acid was 26.3 g/L for 48 h of fermentation.