Ethanol Production from Soybean Fiber, a Co-product of Aqueous Oil Extraction, Using a Soaking in Aqueous Ammonia Pretreatment

Abstract

The effectiveness of soaking in aqueous ammonia (SAA) as a pretreatment method for the conversion of soybean fiber to ethanol via simultaneous saccharification and fermentation (SSF) was investigated. Insoluble fiber is a co-product from oil and protein extraction using two-stage, countercurrent, enzyme-assisted, aqueous extraction processing of full-fat soybean flakes (FFSF) and extruded FFSF. The fiber fractions were soaked in 15 wt% aqueous ammonia at 1:10 solid-to-liquid ratio. The effects of operating variables, including treatment times (6, 12, and 24 h), treatment temperatures (60 and 80 A degrees C), and cellulase loadings (15 and 60 FPU/g-glucan) on the degree of enzymatic hydrolysis were determined. The best SAA conditions were 80 A degrees C for 12 h followed by an enzyme loading of 15 FPU/g-glucan, which produced a 152-mg/g glucose yield after 48 h of hydrolysis. This was 8.7 times the amount produced from the same fiber not pretreated with SAA. The glucose yield increased to 381 mg/g when fiber obtained from extruded FFSF was submitted to SAA. SAA (80 A degrees C, 12 h) on extruded fiber subjected to SSF increased ethanol yield from 0.06 g of ethanol/g [40% of theoretical yield] (for non SAA pretreated fiber) to 0.25 g of ethanol/g [92% of theoretical yield]. The combination of extrusion and SAA was an efficient means for converting the fiber-rich soybean fraction into ethanol.