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Extrusion Pretreatment and Enzymatic Hydrolysis of Soybean Hulls

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Bioenergy Engineering, 11-14 October 2009, Bellevue, Washington  BIO-097989.(doi:10.13031/2013.28870)
Authors:   Veeramani Karuppuchamy, Kasiviswanathan Muthukumarappan
Keywords:   Soy hull, Pretreatment, Extrusion, Enzymatic hydrolysis, Sugar recovery, Byproducts

Soybean hull is a major by-product of soybean processing industry and constitutes about 8% of the whole seed. Soy hulls typically contain 52% (w/w) cellulose and 8-10% (w/w) water, the remaining 38-40% (w/w) being comprised of hemicellulose, lignin, proteins, salts and minerals. The primary purpose of pretreatment is to make the cellulosic biomass amenable to the action of cellulose enzyme. Extrusion is an unexplored pretreatment, but can be used in a commercial scale if more research is being done. In this research, we studied the use of extrusion pretreatment on the enzymatic hydrolysis of soybean hulls. The soybean hulls were pretreated in a single screw extruder. The effects of extrusion temperature, screw speed of the extruder and moisture content of the hulls were investigated. The extruder was operated at four barrel temperatures (100, 110, 120 and 130C) with four screw speeds (50, 60, 70 and 80 rpm) for three soy hull moisture contents (10, 12.5 and 15% w.b). The extruded samples were subjected to enzymatic hydrolysis and sugars were measured using HPLC (NREL/TP-510-42623). From the analysis, it was found that, the extruder parameters and soy hull moisture content had an influence on the sugar recovery from soy hull. The soy hull extruded at 130C and 60 rpm with 12.5% w.b. moisture content resulted in 62.5%, 68.6% and 62.4% recoveries for glucose, xylose and combined sugar respectively. These glucose, xylose and combined sugar recoveries are 1.7, 1.4 and 1.8 times more than the completely untreated (control) samples. Byproducts like xylitol and acetic acid were also found in most of the pretreated samples.

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