Study On Enzymatic Hydrolysis Of Rice Straw Promoted By Pretreatment With White Rot Fungi

Utilization of agricultural straw fiber to produce fermentable monomeric sugaroffers a great potential for reducing the raw material cost and increasing thealternatives of raw material. Unlike crops which can be easily hydrolyze into themonomeric sugar, pretreatment is required for the utilization of lignocellulosicmaterials to attain relatively high enzymatic saccharification.In this paper, Coriolus versicolor，Pleurotus Ostreatus，Pleurotus sajor-cajuwere used to pretreat rice staw. The effect of biological pretreatment with5white rotfungi, Coriolus versicolor4,6,9, Pleurotus ostreatus and Pleurotus sajor-caju onthe ligninolytic enzyme and cellulase production, chemical composition, lignindegradation selectivity index enzymatic hydrolysis efficiency of rice straw wereevaluated.Laccase, Mn-peroxidase and cellulase were detected during the pretreatment(0-50day). The activity of Lingin-peroxidase was not detected. The highest Lacactivity2244U/L was obtained after20day cultivation by Pleurotus sajor-caju, andthe highest Mnp activity771U/L was obtained after40day cultivation by Pleurotusostreatus.Selective degrading index (SI) of Pleurotus ostreatus increased over thepretreatment time and went up to1.87(in50day), and it showed better selectivedegrading ability than other4white rot fungi. The influences of different carbonresources on lignocellulose degradation, selectivity index differed a lot. In the3carbon resources, selectivity index of lignin degradation were promoted much bywheat bran. Selectivity index of lignin was improved from1.86to2.64by wheatbran.Coriolus versicolor4, Pleurotus ostreatus and Pleurotus sajor-caju revealed agood pretreatment efficiency. After enzymatic hydrolysis, total sugar conversion of59.6%,56.3%,54.4%can be achieved by using the substrate pretreated withCoriolus versicolor4, Pleurotus ostreatus and Pleurotus sajor-caju under thecondition of pretreatment time50day and cellulase loading of20FPU/(g substrate),respectively.Total sugar conversion from52.1%to64.0%by wheat bran load of15%.The final fermentable sugar yield (48h) was negatively related to the lignin contentof rice straw pretreated by white rot fungi significantly is in spite of pretreated rice straw.Considering the results of XRD, SEM and nitrobenzene oxidation oflignocellulose degradation, it can be presumed that strain Pleurotus sajor-cajudegraded lignocellulose by oxidative cracking. Yield of nitrobenzene oxidation oflignocellulose decreased over the pretreatment time and went down from29.4%to13.5%(in50day).Guaiacyl and p-hydroxyphenyl lignin unit were dergradedpreferentially by Pleurotus sajor-caju, the results indicated that S/G ratio affectedthe total sugar conversion, and the higher was associated with a lower S/G ratio.Crystallinity of rice straw pretreated by Coriolus versicolor4went from50.5%up to59.0%, Crystallinity of rice straw pretreated by Coriolus versicolor9and PleurotusOstreatus decreased from50.5%to28.3%,41.7%respectively; the change ofcrystallinity of rice straw during the pretreatment didn’t show obvious effect ontotal sugar conversion of rice straw. SEM showed that rice straw surfacepretreateated by Coriolus versicolor，Pleurotus sajor-caju，Pleurotus ostreatusexsited many cracks and holes area, which increased the specific surface area andpromoted the total sugar conversion.