Jan B Kristensen

Publications (4)12.18 Total impact

• Source

  Available from: PubMed Central

  Article: Yield-determining factors in high-solids enzymatic hydrolysis of lignocellulose.

  Jan B Kristensen, Claus Felby, Henning Jørgensen
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  ABSTRACT: Working at high solids (substrate) concentrations is advantageous in enzymatic conversion of lignocellulosic biomass as it increases product concentrations and plant productivity while lowering energy and water input. However, for a number of lignocellulosic substrates it has been shown that at increasing substrate concentration, the corresponding yield decreases in a fashion which can not be explained by current models and knowledge of enzyme-substrate interactions. This decrease in yield is undesirable as it offsets the advantages of working at high solids levels. The cause of the 'solids effect' has so far remained unknown. The decreasing conversion at increasing solids concentrations was found to be a generic or intrinsic effect, describing a linear correlation from 5 to 30% initial total solids content (w/w). Insufficient mixing has previously been shown not to be involved in the effect. Hydrolysis experiments with filter paper showed that neither lignin content nor hemicellulose-derived inhibitors appear to be responsible for the decrease in yields. Product inhibition by glucose and in particular cellobiose (and ethanol in simultaneous saccharification and fermentation) at the increased concentrations at high solids loading plays a role but could not completely account for the decreasing conversion. Adsorption of cellulases was found to decrease at increasing solids concentrations. There was a strong correlation between the decreasing adsorption and conversion, indicating that the inhibition of cellulase adsorption to cellulose is causing the decrease in yield. Inhibition of enzyme adsorption by hydrolysis products appear to be the main cause of the decreasing yields at increasing substrate concentrations in the enzymatic decomposition of cellulosic biomass. In order to facilitate high conversions at high solids concentrations, understanding of the mechanisms involved in high-solids product inhibition and adsorption inhibition must be improved.
  Biotechnology for Biofuels 02/2009; 2(1):11. · 6.09 Impact Factor
• Source

  Available from: PubMed Central

  Article: Cell-wall structural changes in wheat straw pretreated for bioethanol production.

  Jan B Kristensen, Lisbeth G Thygesen, Claus Felby, Henning Jørgensen, Thomas Elder
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  ABSTRACT: Pretreatment is an essential step in the enzymatic hydrolysis of biomass and subsequent production of bioethanol. Recent results indicate that only a mild pretreatment is necessary in an industrial, economically feasible system. The Integrated Biomass Utilisation System hydrothermal pretreatment process has previously been shown to be effective in preparing wheat straw for these processes without the application of additional chemicals. In the current work, the effect of the pretreatment on the straw cell-wall matrix and its components are characterised microscopically (atomic force microscopy and scanning electron microscopy) and spectroscopically (attenuated total reflectance Fourier transform infrared spectroscopy) in order to understand this increase in digestibility. The hydrothermal pretreatment does not degrade the fibrillar structure of cellulose but causes profound lignin re-localisation. Results from the current work indicate that wax has been removed and hemicellulose has been partially removed. Similar changes were found in wheat straw pretreated by steam explosion. Results indicate that hydrothermal pretreatment increases the digestibility by increasing the accessibility of the cellulose through a re-localisation of lignin and a partial removal of hemicellulose, rather than by disruption of the cell wall.
  Biotechnology for Biofuels 02/2008; 1(1):5. · 6.09 Impact Factor
• Source

  Available from: usda.gov

  Article: Cellulose-water interactions during enzymatic hydrolysis as studied by time domain NMR.

  Claus Felby, Lisbeth G. Thygesen, Jan B Kristensen, Henning Jørgensen, Thomas Elder
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  ABSTRACT: The different states and locations of water within the cellulose matrix can be studied by the use of time domain low field NMR. In this work we show how the state and location of water associated with cellulose in filter paper fibers are affected by enzymatic hydrolysis. Three locations of water were identified in the filter paper; (1) bound water associated with the microfibril surfaces and (2) water in the cell wall or cellulose matrix and (3) capillary water in the lumens and between fibers. The different mechanisms of cellulase enzymes can be seen in their effect on the cellulose-water interactions and the synergistic effects between endo- and exo enzymes can be easily detected by time domain NMR. An interesting observation is that it is possible to link the state and location of water within the cellulose fiber with structural changes upon enzymatic hydrolysis.
• Article: Use of surface active additives in enzymatic hydrolysis of wheat straw lignocellulose

  Jan B. Kristensen, Johan Börjesson, Maria H. Bruun, Folke Tjerneld, Henning Jørgensen
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  ABSTRACT: Monocot residues such as corn stover and straw are often not fully exploited and constitute a potential substrate for bioethanol production. However, a number of factors such as high enzyme loadings make large-scale utilization economically difficult. Addition of non-ionic surfactants and poly(ethylene glycol) to enzymatic hydrolysis of various lignocellulosic substrates has been found to increase the conversion of cellulose into soluble, fermentable sugars. We have shown that surfactants are able to increase cellulose conversion with up to 70%. This provides an opportunity of decreasing enzyme loading while retaining the same degree of hydrolysis. Investigations of five wheat straw substrates produced with different pretreatment methods revealed that surfactants have a more pronounced effect on acid and steam treated straw than, e.g. ammonia and hydrogen peroxide treated straw. Thus, lignin content is not directly proportional with the potential surfactant effect. Studies of adsorption of cellulases support the theory that the main mechanism behind the surfactant effect is prevention of unspecific adsorption of enzyme on the substrate lignin. This is believed to be due to hydrophobic interaction between lignin and the surfactant, causing steric repulsion of enzyme from the lignin surface. More research is needed to reveal which factors influence enzyme and surfactant adsorption.
  Enzyme and Microbial Technology.