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 C), and cellulase
loadings (15 and 60 FPU/g-glucan) on the degree of enzymatic
hydrolysis were determined. The best SAA conditions
were 80 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 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.