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

Abstract

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.

Optimization of Saccharification of Biological Pre-Treated Rice Straw by Response Surface Methodology

“…Increased consistency, product inhibition and reduced surface contact between the enzyme and the substrate are responsible for the low reducing sugars content at high substrate concentrations. The extent of substrate inhibition is dependent on the ratio of the total substrate to total enzyme loaded (Xin et al, 2010;Wang et al, 2011). The effect of interaction of temperature and pH, with a substrate concentration (8.75%, w/v) at central level is presented in Figure 2 (b).…”

Comparison of industrially viable pretreatments to enhance soybean straw biodegradability

“…2 and Table 1), which indicates that higher amount of no polysaccharide constituents were removed in this pretreatment. It is well known that high lignin removal enhances enzyme action by increasing the disruption of biomass structure (Limayema and Ricke, 2012) and reducing the irreversible adsorption of hydrolytic enzymes on lignin surface (Wang et al, 2011). Moreover, high hemicelluloses retention increases polysaccharide availability for the following enzymatic hydrolysis (Cabrera et al, 2014).…”

The Effect of Substrate Loading On Simultaneous Saccharification And Fermentation Process For Bioethanol Production from Oil Palm Empty Fruit Bunches

“…So it required an additional time of SSF process to convert the remaining glucose into ethanol. It is because high solid loadings may result in limited cellulose conversions in enzymatic hydrolysis [17] or in SSF stages, owing to mass transfer limitation. The efficiency of enzymatic digestibility and fermentation is significantly reduced at high concentrations of pretreated biomass, as mixing becomes difficult with increased viscosity [29].…”

“…Increasing substrate loading in hydrolysis and fermentation step is one of the most important challenges produces ethanol more economical [15]. However, high substrate concentration has also causes a larger levels of inhibiting compounds [16], diffusional enzymes problems [17], endproduct inhibition [18],stirring and mixing limitations by viscosity increase [19] or possible mass transfer limitations appearing above 20% insoluble solids concentration [20]. Thus, in this study it will be investigated the different strategies for high substrate loading in SSF process of bioethanol production from EFBs.…”