Effect Of Sequential Action Of Fiber Degrading Enzymes On The Degradation Of Corn Stover

Corn stover is one of the most agricultural residue abundances over the world.However,it is extremely prevented from microbial and enzymatic degradation into its monomers because of its complex chemical and physical structure.Therefore,some pretreatment activities are required to be performed in order to enhance its degradability for more efficient utilization either as a source for biofuel production or feed for livestock industry.Recent studies have indicated increases in enzymatic hydrolysis of corn stover through the effective steam explosion.In order to degrade corn stover,a large variety of enzymes with different specificities are required.However,each enzyme has its reaction condition such as optimal pH and temperature to express its maximum activity.We hypothesis that the best sequence of enzymes reaction could influence the degradation of corn stover.Therefore,the objective of this study was to investigate the effect of enzymes sequence action on the degradation of corn stover.In this study two experiments were carried out.The first experiment was by using raw corn stover as substrate,however,the second experiment was by using steam exploded pretreated corn stover as substrate.In the first 1^st experiment a complete randomized design was used for this study.Number of treatments was 24?4*3*2*1?and 3 replications.Four enzymes were used,cellulase?Cel??pH 4.8 at 50°C?,hemicellulase?Hem??pH 5 at 50°C?,pectinase?Pec??pH4 at 50°C?and laccase?Lac??pH 3 at 30°C?.This was subsequently submitted to enzymes sequence digestion following four steps?6 h incubation for each step?during which a single enzyme in each step was evaluated.The substrate?raw corn stover?was placed in a sodium acetate buffer with enzyme.The supernatant was then collected in each step for further chemical analysis.The results showed that there was a significant difference at P<0.05 between treatments,suggesting that sequential action of fiber-degraded enzymes affected the release of reducing sugar?mainly glucose and xylose?as well as the release of phenol from corn stover.The best enzymes sequence?in term of the total reducing sugar in different steps?was Hem-Cel-Pec-Lac?2.2 mg/ml?at P<0.05,however the lowest enzymes sequence was Lac-Pec-Hem-Cel?0.8mg/ml?at P<0.05.Almost all the first steps in the process showed an increasing level of reducing sugar except the step which started with Lac were less reducing sugar level was observed.Similarly,xylose showed a higher level in all the processes in the first steps regardless of the enzyme type.It was observed that glucose production was totally depended on the position of Cel in the enzymes sequence.Therefore,enzymes sequence action may be a useful method for corn stover to improve its degradation as feed stock.However,in the 2^nd experiment also a completely randomized design with 24?4*3*2*1?treatments and 3 replications,all the materials in this study were made uniform.Four enzymes were used;cellulase?Cel?,hemicellulase?Hem?,pectinase?Pec?and laccase?Lac?.Enzymes sequence digestion was then carried out in four steps and at each step,a single enzyme was used.The corn stover was first submitted to steam pretreatment,and then the efficacy of sequential fiber-degraded enzymes was evaluated.Enzymes sequence action altered the physical and chemical structure of corn stover as revealed by scanning electron microscopy?SEM?and X-ray respectively.It also increased release of reducing sugar,total phenol and xylose content while decreasing glucose content.The results showed that there were significant differences between treatments?P<0.05?,suggesting that sequential action of fiber-degraded enzymes affected the chemical composition of corn stover.The best enzymes sequence was Hem-Cel-Pec-Lac with reducing sugar?43.34mg/ml?at P<0.05,glucose?1mg/ml?at P<0.05 and xylose?14.7mg/ml?at P<0.05,galacturonic acid?0.06mg/ml?at P<0.05and Total phenol?20.6mg/ml?at P<0.05.Therefore,enzymes sequence action may be a useful method for corn stover to improve its degradation as feed stock.Also,the study has the potential to increase our understanding about the utilization and optimization of fiber-degrading enzymes.