Background Lignocellulosic biomass is considered as a potential source for sustainable biofuels. In the conversion process, a pretreatment step is necessary in order to overcome the biomass recalcitrance and allow for sufficient fermentable sugar yields in enzymatic hydrolysis. Steam explosion is a well known pretreatment method working without additional chemicals and allowing for efficient particle size reduction. However, it is not effective for the pretreatment of softwood and the harsh conditions necessary to achieve a highly digestible cellulose fraction lead to the partial degradation of the hemicellulosic sugars. Previous studies showed that the autohydrolysis pretreatreatment of softwood can benefit from the addition of 2-naphthol. This carbocation scavenger prevents lignin repolymerisation leading to an enhanced glucose yield in the subsequent enzymatic hydrolysis. Results In order to prevent the degradation of the hemicellulose, we investigated in this study a two-stage 2-naphthol steam explosion pretreatment. In the first stage, spruce wood is pretreated at a severity which is optimal for the autocatalytic hydrolysis of the hemicellulose. The hydrolyzate containing the solubilized sugars is withdrawn from the reactor and the remaining solids are pretreated with different amounts of 2-naphthol in a second stage at a severity that allows for high glucose yields in enzymatic hydrolysis. The pretreated spruce was subjected to enzymatic hydrolysis and to simultaneous saccharification and fermentation (SSF). In the first stage, the maximal yield of hemicellulosic sugars was 47.5% at a pretreatment severity of log = 3.75 at 180 °C. In the second stage, a 2-naphthol dosage of 0.205 mol/mol lignin C 9 -unit increased the ethanol yield in SSF with a cellulose loading of 1% using the whole second stage pretreatment slurry by 17% from 73.6% for the control without 2-naphthol to 90.4%. At a higher solid loading corresponding to 5% w/w cellulose, the yields decreased due to higher concentrations of residual 2-naphthol in the biomass and the pretreatment liquor, but also due to higher concentrations of potential inhibitors like HMF, furfural and acetic acid. Experiments with washed solids, vacuum filtered solids and the whole slurry showed that residual 2-naphthol can inhibit the fermentation as a single inhibitor but also synergistically together with HMF, furfural and acetic acid. Conclusions This work shows that a two-stage pretreatment greatly enhances the recovery of hemicellulosic sugars from spruce wood. The presence of 2-naphthol in the second pretreatment stage can enhance the ethanol yield in SSF of steam explosion pretreated softwood at low cellulose concentrations of 1% w/w. However, with higher solid loadings of 5% w/w cellulose, the ethanol yields were in general lower due to the solid effect and a synergistic inhibition of HMF, furfural, acetic acid with residual 2-naphthol. The concen...
For the production of second generation biofuels from lignocellulosic biomass, pretreatment of the biomass feedstock is necessary to overcome its recalcitrance in order to gain fermentable sugars. Due to many reasons, steam-explosion pretreatment is currently the most commonly used pretreatment method for lignocellulosic biomass on a commercial scale [S. Brethauer and M. H. Studer, CHIMIA, 2015, 69, 572-581]. In contrast to others, we showed that the explosive decompression at the end of this pretreatment step can have a positive influence on the enzymatic digestibility of softwood, especially in combination with high enzyme dosages [T. Pielhop, et al., Biotechnology for Biofuels, 2016, 9, 152]. In this study, the influence of the explosive decompression on the enzymatic digestibility of hardwood and herbaceous plants was systematically studied. Beech and corn stover were pretreated under different pretreatment conditions and enzymatically hydrolysed with different enzyme dosages. The maximum enhancement of the digestibility of corn stover was 16.53% after a 2.5 min pretreatment step at 15 barg steam pressure. For beech, a maximum relative enhancement of 58.29% after a 10 min pretreatment step at 15 barg steam pressure could be reached. With this, we show that the explosive decompression can also enhance the enzymatic cellulose digestibility of hardwood and herbaceous plants.
A-6400-073 (01/97) GEF321 * ** actual remaining capacity as observed. theoretical ultimate capacity, assuming optimal packing density.
Keloids are fibroproliferative scars that invade the surrounding tissue beyond the original wound site. The cellular and molecular mechanism for the pathogenesis of keloid scars are still unknown. We investigated the role of the transcription factor Twist, a key regulator in epithelial-to-mesenchymal transition, its upstream regulators, and downstream targets, which are associated with self-renewal, proliferation and invasion, in keloid tissue. Multicolour immunofluorescence microscopy was performed on frozen tissue sections of keloid scars, normal scars and normal skin staining for Twist, and related molecules such as Bmi1, active b-catenin and inhibitor of differentiation 1 (Id1). Staining of these markers was quantified using Metamorph software. Endothelial and mesenchymal cells were identified and inflammatory infiltrates were investigated using markers for T cells, B cells, and macrophages. Our results reveal remarkable upregulation of Twist expression in keloids compared to normal scar and normal skin. Furthermore, we show a significant increase in expression of Bmi1, active
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