High monomeric sugar yields from enzymatic hydrolysis of soybean meal and effects of mild heat pretreatments with chelators.

Defatted soybean meal has 30-35% oligo-/polymeric carbohydrates and approximately 50% proteins. Enzymatic carbohydrate monomerization enables easy separation to enrich protein content, reduces indigestibility concerns, and facilitates use of carbohydrate as fermentation feedstock. Among soybean carbohydrates, pectin and glucan are more recalcitrant to hydrolyze. To destabilize Ca2+-bridged junctures in pectin, effects of 3 chelators ethylenediaminetetraacetic acid (EDTA), sodium hexametaphosphate (HMP) and citric acid under 2-h 90 °C pretreatments were investigated here. Citric acid was the most effective while EDTA decreased enzymatic hydrolysis. In a 3-factor 2-level factorial study, heat (90 °C, 2 h) and citric acid (10 g/L) pretreatments and cellulase supplementation (10 FPU/g) were found to increase yields of all monosaccharides, to 86.8 ± 5.2% glucose, 98.1 ± 1.6% xylose, 87.5 ± 5.2% galactose, 83.6 ± 1.6% arabinose, and 91.4 ± 3.1% fructose + mannose. The largest percentage improvements were for arabinose (382%), mannose (113%) and glucose (51%). Achieving high monosaccharide yields greatly increases value of soybean carbohydrate as fermentation feedstock.