Lignocellulosic hydrolysates

Almeida JRM, Modig T, Petersson A, Hahn-Hagerdal B, Liden G, Gorwa-Grauslund MF. 2007. Increased tolerance and conversion of inhibitors in lignocellulosic hydrolysates by Saccharomyces cerevisiae. J Chem Technol Biotech 82 340-349. 

The genetically engineered Saccharomyces cerevisiae 424A (LNH-ST) was used for fermentation of lignocellulosic hydrolysates to ethanol. S. cerevisiae 424A (LNH-ST) was constructed by integrating multiple copies of XD, XR, and XK into the chromosomes of S. cerevisiae ATCC 4124 accord-... 

Fermentability of Different Lignocellulosic Hydrolysates by S. cerevisiae 424A(LNH-ST) ... 

Ethanol production depends not only on the sugar yield, but also on the fermentability of the solution. To investigate the fermentability of the pretreated com stover, fermentations were performed with baker s yeast. Baker s yeast has often been proposed as the best organism for the fermentation of lignocellulosic hydrolysates (28,29) and has the advantages that it is quite robust and was found to be less sensitive to inhibitors than cultivated yeast (30,31). 

The breakdown of furan aldehydes leads to the formation of formic and levulinic acid. Moreover, acetic acid is formed during the degradation of hemicellulose. Partial breakdown of lignin can generate a variety of phenolic compounds (23), which also inhibit S. cerevisiae (14,15). In contrast to furan aldehydes and aliphatic acids, the toxic effect of specific phenolic compounds is highly variable (15). Different raw materials and different approaches to prepare lignocellulose hydrolysates will result in different concentrations of the fermentation inhibitors (16,17). 

It is well known that phenolic compounds are important inhibitors in hydrolysates prepared from hardwood (27) as well as softwood (20). The hydrophobicity of the matrix is likely to be an important property that contributes to the ability of an ion-exchange resin to remove phenols. Although the knowledge regarding the suitability of different methods to determine phenolics in lignocellulose hydrolysates has increased (28), the quantification of phenolics and the correlation with the inhibitory effect is still a challenging task, because hydrolysates contain a wide variety of phenolic compounds that have very different toxic effects. 

Performance of Some Recombinant and Native Xylose-Fermenting Organisms Under Laboratory Conditions and on Native Lignocellulosic Hydrolysates... 

Fig. 8 a, b. a PCA classification of lignocellulose hydrolysates from pine, spruce, aspen and birch using a combination of MOS, MOSFET and CP sensors, b Prediction of the ferment-ability of the same hydrolysates expressed as specific ethanol production rate using ANNs with topologies adapted to the sensor array (from [34] with permission of ACS)... 

Hahn-Hagerdal, B., Linden, T., Senac, T., and Skoog, K., Ethanolic fermentation of pentoses in lignocellulose hydrolysates. Appl Biochem Biotechnol 1991, 28-29, 131-44. 

The unfavorable energy balance notwithstanding, the fermentation of ethanol, as well as other chemicals, from lignocellulose hydrolysate is considered highly desirable by some to avoid competition with food production. We note, however, that the large scale processing of waste lignocellulose runs counter to sensible... 

Linden, T., Hahn-Gaegerdal, B. (1989). Fermentation of lignocellulose hydrolysates with yeasts and xylose isomerase. Enzyme and Microbial Technology, II, 583-589. 

According to Shi et al. [26], there is a flmdamental difference between the respiratory machinery supporting xylose and glucose metabolism using P. stipitis wild-type CBS 6054. However, addition of electron acceptors such as ketones and aldehydes in the medium [27] reduces xylitol formation. Such compounds are present also in lignocellulose hydrolysates... 

As a result, a substantial fraction of the monosaccharides in lignocellulose hydrolysates from hardwood and agricultural residues consists of xylose. Consequently, ethanolic fermentation of xylose is of major concern for the efficient utilization of lignocellulosic hydrolysates to produce fuel ethanol. 

Fig. 2. Fermentation inhibitors in lignocellulose hydrolysates. Some of the possible pathways by which the inhibitors are generated, either by acid hydrolysis or in the ethanolic fermentation, are indicated in the figure...

Inhibitory furaldehydes in lignocellulose hydrolysates include 2-furaldehyde (furfural) and 5-hydroxymethyl-2-furaldehyde (HMF) (Fig. 2). The concentrations of furfural and HMF in lignocellulose hydrolysates are highly dependent on the raw material and on the conditions used for acid hydrolysis. Softwood acid hydrolysates contain low amounts of furfural compared with HMF [58]. Hardwood hydrolysates, which contain high concentrations of pentoses, the precursors to furfural, contain more similar amounts. Several recent investigations [102-105] deal with the effect of the furaldehydes on S. cerevisiae and the conversion of furfural to furfuryl alcohol and HMF to 5-hydroxymethyl-fur-furyl alcohol by S. cerevisiae. The presence of the furaldehydes causes lag phases in the formation of biomass and ethanol. 

Palmqvist, E. and Hahn-Hagerdal, B. (2000) Eermentation of lignocellulosic hydrolysates. II inhibitors and mechanisms of inhibition. Bioresour. TechnoL, 74 (1), 25-33. 

Demeke, M.M., Dietz, H., Li, Y., Foulquie-Moreno, M.R. et oL (2013) Development of a D-xylose fermenting and inhibitor tolerant industrial Saccharomyces cerevisiae strain with high performance in lignocellulose hydrolysates using metabolic and evolutionary engineering. Biotechnol. Biofuels, 6, 89. 

Palmqvist E, Hahn-Hagerdal B. (2000). Fermentation of lignocellulosic hydrolysates. 1 inhibition and detoxification. Bioresour Technol, 74, 17-24. 

Abiksson B, Rose SH, van Zyl WH, Sjode A, Nilvebrant NO, Jonsson LJ. (2009). Cellulase production from spent lignocellulose hydrolysates by recomhimnt Aspergillus niger. Appl Environ Microbiol, 75(8), 2366-2374. 

Fujitomi K, Sanda T, Hasunuma T, Kondo A. (2012). Deletion of the PH013 gene in Sac-charomyces cerevisiae improves ethanol production from lignocellulosic hydrolysate in the presence of acetic and formic acids, and furfural. Bioresour Technol, 111, 161-166. 

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