Production of fermentable sugars from corn fiber using soaking in aqueous ammonia (SAA) pretreatment and fermentation to succinic acid using Escherichia coli AFP184

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 °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 °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.