A comparison between hot liquid water and steam fractionation of corn fiber

Dried, milled corn fiber (0.2-0.5 kg) was fractionated by treatment with ei ther hot liquid water (3-4 kg) at low solids loadings (5-10%) or steam (0.1 -0.4 kg) at high solids loadings (> 50%) at 210-220 degreesC for 2 min, usi ng the same novel process equipment. Pentosan recovery and inhibition of ye ast fermentation were evaluated and compared. In addition, the reactivity o f pretreated fiber with respect to enzymatic hydrolysis was evaluated using a simultaneous saccharification and fermentation (SSF) system consisting o f P-glucosidase-supplemented Trichoderma reesei cellulase together with fer mentation by Saccharomyces cerevisiae. Greater solubilization was achieved at 215 degreesC with hot liquid water at 5% solids loading than with steam at 70% solids loading (54% solubilization vs 37%). The lignocellulosic resi due from this hot liquid water fractionation was enriched in glucan. Conver sely, the steam fractionation caused no significant change in the fraction of glucan in the residue, relative to the feed material. In both cases, the pentosan fraction of the lignocellulosic residue was reduced, with the ste am fractionation resulting in a larger reduction of these carbohydrates. St eam fractionation (70% solids loading) resulted in much lower pentosan reco very (as monosaccharides after posthydrolysis) than fractionation with hot liquid water at 5% solids loading (40% vs 82%). In both cases, the majority of the solubilized pentosans existed as oligomers (> 80%). These recoverie s indicate that the monosaccharides are protected while in the form of olig omers because recoveries of largely oligomeric carbohydrates are higher tha n recoveries of monomeric xylose pretreated under similar conditions. The l ignocellulosic residues from fractionation at 215 degreesC with hot liquid water at 5% solids loading and with steam at 70% solids loading were both r eactive to enzymatic hydrolysis, exhibiting 86 and 90% conversion of glucan to ethanol respectively vs 64% conversion with untreated corn fiber, obtai ned by SSF at an enzymatic loading of 15 FPU cellulase/g of cellulose. The liquid product (extract) from the hot liquid water fractionation did not in hibit the final yield of glucose fermentation by S. cerivisiae, while the l iquid product from the steam fractionation did.