Production Of Xylooligosaccharides And Monosaccharides From Lignocelluloses By Two-step Enzymatic Hydrolysis

Xylooligosaccharides?XOS?,as an emerging prebiotics,have a great deal of physiological activities,including lowering cholesterol,decreasing the risk of diabetes,controlling the banlance of blood sugar and immunomodulation.At present,alkaline extraction combined with xylanase hydrolysis was recognized as a major method to produce XOS.Nevertheless,the process could produce alkali waste liquid and resulted in environmental contamination.In this work,poplar and corncob were pretreated with hydrogen proxide-acetic acid?HPAC?to selectively remove lignin,and xylan in the pretreated lignocellulose was hydrolyzed by xylanase to produce XOS.The effects of pretreatment condition and xylanase dosage on the XOS yields were investigated.The solid residues after xylanase hydrolysis were further hydrolyzed by cellulases?CEL?to produce monosaccharides.HPAC pretreatment of poplar using 60%HPAC with 200 m M H₂SO₄ as catalyst showed a good delignifiability with a lignin removal of 88.75%and a low corbonhydrate removal?<2%?.After HPAC pretreatment,the crystallinity and the O/C ratio of poplar increased.Higher XOS yields were obtained from HPAC-pretreated poplar prepared using200 m M H₂SO₄ as catalyst than that with 50 m M H₂SO₄.Within the tested conditions,the highest XOS yield of 19.8%was obtained from 60%HPAC with 200 m M H₂SO₄ using10,000 nkat XYL per gram dry matter?DM?for 24 h,and the xylose/XOS was only 0.14,indicating the high purity of the XOS preparation.Xylobiose,xylotriose and xylotetraose yields were the main oligosaccharides in the hydrolysates from XYL.Higher glucose?75.2%?and xylose?61.4%?yields were obtained from poplar pretreated using 60%HPAC with 50m M H₂SO₄ as catalyst than those?33.3%glucose yield and 43.4%xylose yield?with 200m M H₂SO₄as catalyst using 10 mg CEL/g DM.With the increase of HPAC concentration,the acid insoluble lignin content of corncob decreased.The H₂SO₄ concentration in HPAC pretreatment played an important role in lignin removal,and a higher H₂SO₄concentration showed stronger lignin removal ability after HPAC pretreatment of corncob.After corncob was pretreated by 75%HPAC with 75m M H₂SO₄ as catalyst,a XOS yield of 27.81%was achieved by 10,000 nkat XYL/g DM.The xylose/XOS was only 0.09,indicating a high XOS purity was obtained from HPAC-pretreated corncob.Xylobiose,xylotriose and xylotetraose yields were the main oligosaccharides in the XOS preparation.A glucose yield of 79.07%was obtained from corncob pretreated by 100%HPAC with 50 m M H₂SO₄ as catalyst using 10 mg CEL/g DM.In this work,XOS and monosaccharides were efficiently produced from poplar and corncob after HPAC pretreatment.The XOS was produced from HPAC-pretreated lignocelluloses without xylan extraction and high yields of XOS with high purity were achived.The data here suggested that XOS and monosaccharides were efficiently produced from lignocelluloses by two-step enzymatic hydrolysis with less pollution,and the results in this work also provided scientific base for high value-added utilization of lignocelluloses.