Sequential Action of Different Fiber-Degrading Enzymes Enhances the Degradation of Corn Stover

Abstract

Corn stover is one of the most agricultural residue abundances over the world; however, it is extremely prevented from microbial and enzymatic degradation into monomers because of the complex chemical and physical structure. In order to degrade corn stover, a large variety of enzymes with different specificities are required. However, each enzyme has its own reaction condition such as optimal pH and temperature to express its maximum activity. We hypothesize that the best sequence of an enzyme reaction could influence the degradation of corn stover. Therefore, the objective of this study was to investigate the effect of enzyme sequence action on the degradation of corn stover. A complete randomized design was used for this study. Four enzymes were used, cellulase (Cel) (pH 4.8 at 50 °C), hemicellulase (Hem) (pH 5 at 50 °C), pectinase (Pec) (pH 4 at 50 °C) and laccase (Lac) (pH 3 at 30 °C). This was subsequently submitted to enzyme 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 sodium acetate buffer with an 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-degrading enzymes affected the chemical composition of corn stover. The best enzyme sequence (in terms of the total reducing sugar in different steps) was Hem-Cel-Pec-Lac (2.2 mg/mL) at p < 0.05; however, the worst enzyme sequence was Lac-Pec-Hem-Cel (0.8 mg/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 where a lower 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 dependent on the position of Cel in the enzyme sequence. Therefore, enzyme sequence action may be a useful method for corn stover to improve its degradation as feed stock.