Sugar Yield In Enzymatic Hydrolysis Research Articles

Study on the Decreased Sugar Yield in Enzymatic Hydrolysis of Cellulosic Substrate at High Solid Loading

Current technology for conversion of biomass to ethanol is an enzyme-based biochemical process. In bioethanol production, achieving high sugar yield at high solid loading in enzymatic hydrolysis step is important from both technical and economic viewpoints. Enzymatic hydrolysis of cellulosic substrates is affected by many parameters, including an unexplained behavior that the glucan digestibility of substrates by cellulase decreased under high solid loadings. A comprehensive study was conducted to investigate this phenomenon by using Spezyme CP and Avicel as model cellulase and cellulose substrate, respectively. The hydrolytic properties of the cellulase under different substrate concentrations at a fixed enzyme-to-substrate ratio were characterized. The results indicate that decreased sugar yield is neither due to the loss of enzyme activity at a high substrate concentration nor due to the higher end-product inhibition. The cellulase adsorption kinetics and isotherm studies indicated that a decline in the binding capacity of cellulase may explain the long-observed but little-understood phenomenon of a lower substrate digestibility with increased substrate concentration. The mechanism how the enzyme adsorption properties changed at high substrate concentration was also discussed in the context of exploring the improvement of the cellulase-binding capacity at high substrate loading.

Microwave-assisted organic acid pretreatment for enzymatic hydrolysis of rice straw

Pretreatment of lignocellulosic materials is considered a critical step in the production of cellulosic ethanol because it can significantly break the structure and remove the unwanted components of lignocellulose to improve the hydrolysis efficiency of cellulose. In this study, the microwave-assisted pretreatment method was adopted to treat rice straw as an alternative to conventional pretreatment methods. After pretreatment, the product was further hydrolyzed by cellulase. The influences of acid concentration, solid–liquid ratio, microwave intensity, irradiating time, and catalyst concentration on the removal ratio of lignin were investigated. The optimal conditions of pretreatment were obtained using an orthogonal test. After pretreatment, the infrared spectrum of the solution was tested, and micro-morphology was observed by scanning electron microscopy (SEM). The removal ratio of lignin and the yield of reducing sugar were determined by spectrophotometry. The results indicate that the sequence of influential factors is microwave intensity > solid–liquid ratio > acetic acid concentration > microwave irradiating time. Under optimal conditions (25% acid concentration, 1:15 solid–liquid ratio, 230 W microwave intensity, and 5 min irradiating time), the removal ratios of lignin are 46.1 and 51.54%, and the sugar yields are 71.41 and 80.08% when acetic acid and propionic acid are used as solvents, respectively. The sugar yield was only 35.28% in the blank sample. SEM images reveal that the surface of rice straw changed noticably when microwave-assisted pretreatment is used. This suggests that microwave-assisted organic acid pretreatment is effective in improving the enzymatic hydrolysis sugar yield of rice straw.

Steam Explosion of the SoftwoodPinus Radiatawith Sulphur Dioxide Addition. I. Process Optimisation

Abstract An experimental optimisation procedure has been used to investigate steam explosion of Pinus radiata. Enzymatic digestibility of this softwood is enhanced by steam explosion and addition of sulphur dioxide greatly Improves effectiveness of the process. The effects of the variables time, temperature, and sulphur dioxide level have been described by empirical models. The response parameters modelled are: dry-matter yield; water-insoluble fibre yield; water- soluble sugar yield; enzymatic-hydrolysis sugar yield; and total sugar yield. Near optimal total sugar yields were obtained with the conditions: 3 minutes; 215°C; and 2.55% sulphur dioxide. Under these conditions the steam-exploded fibre was 82% digestible (cellulose to glucose) by the cellulase enzymes used, and a total sugar yield of 57 g./100 g o.d. wood was obtained. This study has shown that softwoods, of which Pinus radiata is typical, can be made as amenable to hydrolysis by cellulase enzymes as hardwoods, which have previously been consi...