Enzymatic hydrolysis pretreated cellulose

The effective pretreatments for enzymatic hydrolysis of cellulose in hardwoods and agricultural residues have been developed over the past 90 years and new or improved ones are still being developed. The initial impetus for pretreatment research was the expansion of a feed base for ruminants (i.e., cattle and sheep). The concentration of pretreatment research on animal feed preparation placed an additional burden on researchers, because the product must be not only fully convertible to animal live-weight, but also nontoxic and palatable. Early feeding trials of pretreated fine sawdust to cattle produced very dismal results (55). This may be the reason, besides the... 

This session deals with recent progress on pretreatment of lignocellu-losic biomass, the peripheral reactions associated with pretreatment, and assessment of the effectiveness of pretreatment by enzymatic hydrolysis. Pretreatment is an essential element of the integral bioconversion process, and its objective is to enhance the susceptibility of cellulosic substrates to the action of cellulase enzymes. 

Enzyme activity loss because of non-productive adsorption on lignin surface was identified as one of the important factors to decrease enzyme effectiveness, and the effect of surfactants and non-catalytic protein on the enzymatic hydrolysis has been extensively studied to increase the enzymatic hydrolysis of cellulose into fermentable sugars [7, 9 19]. The reported study showed that the non-ionic surfactant poly(oxyethylene)2o-sorbitan-monooleate (Tween 80) enhanced the enzymatic hydrolysis rate and extent of newspaper cellulose by 33 and 14%, respectively [20]. It was also found that 30% more FPU cellulase activity remained in solution, and about three times more recoverable FPU activity could be recycled with the presence of Tween 80. Tween 80 enhanced enzymatic hydrolysis yields for steam-exploded poplar wood by 20% in the simultaneous saccharification and fermentation (SSF) process [21]. Helle et al. [22] reported that hydrolysis yield increased by as much as a factor of 7, whereas enzyme adsorption on cellulose decreased because of the addition of Tween 80. With the presence of poly(oxyethylene)2o-sorbitan-monolaurate (Tween 20) and Tween 80, the conversions of cellulose and xylan in lime-pretreated com stover were increased by 42 and 40%, respectively [23]. Wu and Ju [24] showed that the addition of Tween 20 or Tween 80 to waste newsprint could increase cellulose conversion by about 50% with the saving of cellulase loading of 80%. With the addition of non-ionic, anionic, and cationic surfactants to the hydrolysis of cellulose (Avicel, tissue paper, and reclaimed paper), Ooshima et al. [25] subsequently found that Tween 20 was the most effective for the enhancement of cellulose conversion, and anionic surfactants did not have any effect on cellulose hydrolysis. With the addition of Tween 20 in the SSF process for... 

Considering the result from Fig. 1 that (0.1 g Tween 20 + 0.1 g BSA)/g dry solid gave no further increase of cellulose conversion compared with the addition of Tween 20 alone, a conclusion could be drawn that the mechanisms of Tween 20 and BSA on the improvement of enzymatic hydrolysis of pretreated CWR might be similar. If Tween 20 and BSA had significantly different mechanisms on the improvement of enzymatic hydrolysis, higher cellulose conversion should be expected after BSA was added to the solution with Tween 20 at saturation loading of 0.1 g/g dry solid. 

There is much excellent basic work underway on the enzymatic hydrolysis of cellulose. The key factor is the pretreatment required by lignocellulose before it is acted upon at an acceptable rate. In partially delignified pulps, the rate of hydrolysis rises with decreasing lignin content, but pulping the substrate is impractical. 

Kumakura M, Kaetsu I. (1984). Pretreatment by radiation and acids of chaff and its effect on enzymatic hydrolysis of cellulose. Agricultural Wastes, 9, 279-287. 

There has been a substantial effort to model the kinetics of enzymatic hydrolysis of cellulose and (pretreated) lignocellulosic substrates. Bansal et al. (2009) provide a comprehensive review of many of the models that have been developed. Most of these models are strictly empirical or based on highly simplified Michaelis-Menten concepts. Unfortunately, the assumptions commonly used with Michaelis-Menten kinetics models, namely, that reaction takes place in solution and there is a single... 

Azzam, A.M., 1989. Pretreatment of cane bagasse with alkahne hydrogen peroxide for enzymatic hydrolysis of cellulose and ethanol fermentation. Journal of Environmental Science and Health Part B 24 (4), 421—433. 

The production of fuel ethanol from renewable lignocellulosic material ("bioethanol") has the potential to reduce world dependence on petroleum and to decrease net emissions of carbon dioxide. The lignin-hemicellulose network of biomass retards cellulose biodegradationby cellulolytic enzymes. To remove the protecting shield of lignin-hemicellulose and make the cellulose more readily available for enzymatic hydrolysis, biomass must be pretreated (1). 

Corn stover, like lignocellulosic materials in general, is resistant to enzymatic hydrolysis, because of both the tight network in the lignocellulose complex and the crystalline structure of the native cellulose. These difficulties can be overcome by employing a suitable pretreatment (7). 

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