Evaluation of hot compressed water pretreatment and enzymatic saccharification of tulip tree sawdust using severity factors

Evaluating the In Vitro and In Vivo Prebiotic Effects of Different Xylo-Oligosaccharides Obtained from Bamboo Shoots by Hydrothermal Pretreatment Combined with Endo-Xylanase Hydrolysis

Xylo-oligosaccharides (XOS) enriched with high fractions of X2-X3 are regarded as an effective prebiotic for regulating the intestinal microflora. In this study, the original XOS solution was obtained from bamboo shoots through hydrothermal pretreatment under optimized conditions. Subsequently, enzymatic hydrolysis with endo-xylanase was performed on the original XOS solution to enhance the abundance of the X2-X3 fractions. The results demonstrated that hydrothermal pretreatment yielded 21.24% of XOS in the hydrolysate solution, and subsequent enzymatic hydrolysis significantly increased the proportion of the X2-X3 fractions from 38.87% to 68.21%. Moreover, the XOS solutions with higher amounts of X2-X3 fractions exhibited superior performance in promoting the growth of probiotics such as Bifidobacterium adolescentis and Lactobacillus acidophilus in vitro, leading to increased production of short-chain fatty acids. In the in vivo colitis mouse model, XOS solutions with higher contents of X2-X3 fractions demonstrated enhanced efficacy against intestinal inflammation. Compared with the colitis mice (model group), the XOS solution with higher X2-X3 fractions (S1 group) could significantly increase the number of Streptomyces in the intestinal microflora, while the original XOS solution (S2 group) could significantly increase the number of Bacteroides in the intestinal microflora of colitis mice. In addition, the abundances of Alcaligenes and Pasteurella in the intestinal microflora of the S1 and S2 groups were much lower than in the model group. This effect was attributed to the ability of these XOS solutions to enhance species diversity, reversing the imbalance and disorder within the intestinal microflora. Overall, this work highlights the outstanding potential of XOS enriched with high contents of X2-X3 fractions as a regulator of the intestinal microbiota and as an anti-colitis agent.

Role of hydrothermal pretreatment towards sustainable biorefinery

Recently, the world is experiencing a shift from petroleum refineries to biorefineries due to fossil fuel depletion and environmental concerns. To achieve sustainable development of biorefineries and other components of the biofuel production process, eco-friendly and cost-effective approaches are necessary. Therefore, lignocellulosic biomass (LCB) must be exploited in biorefineries for the generation of a broad spectrum of products. The complex structure of LCB prevents its direct saccharification by enzymatic means, so pretreatment is necessary. There are several pretreatment technologies for disrupting the lignocellulosic structure, but hydrothermal pretreatment is the leading pretreatment technology for recovering hemicellulose fraction with a low number of inhibitors and an increased amount of cellulose. The severity of hydrothermal pretreatment plays a principal role in affecting cellulose, hemicellulose, and lignin structure. A detailed account of microwave-assisted hydrothermal pretreatment technologies and the cost-effectiveness, eco-friendliness, and upcoming challenges of this technology for commercialization with the probable solution is presented.

Characterization of the Mechanical and Morphological Properties of Cow Dung Fiber-Reinforced Polymer Composites: A Comparative Study with Corn Stalk Fiber Composites and Sisal Fiber Composites

Natural fibers and their composites have attracted much attention due to the growing energy crisis and environmental awareness. In this work, a natural lignocellulosic fiber was extracted from cow dung waste and its potential use as reinforcing material in resin-based polymer composites was evaluated. For this purpose, cow dung fiber-reinforced composites (CDFC) were fabricated, and their mechanical and morphological properties were systematically investigated and compared with corn stalk fiber composites (CSFC) and sisal fiber composites (SFC). The results showed that the addition of cow dung fibers reduced the density of the polymer composites, increased the water absorption, and enhanced the impact strength and shear strength. The highest impact and shear strengths were obtained at 6 wt.% and 9 wt.% of fiber loading, respectively, which increased by 23.8% and 34.6% compared to the composite without the fibers. Further comparisons revealed that at the same fiber addition level, the CDFC exhibited better mechanical properties than the CSFC; notably, the CDFC-3 (adding 3 wt.% of fiber loading) had an impact strength closer to the SFC-3. Furthermore, an SEM analysis suggested that the cow dung fibers exhibited a rough and crinkly surface with more node structures, and presented good interfacial bonding with the composite matrix. This work revealed that cow dung fibers are a promising candidate as reinforcement for resin-based polymer composites, which promotes an alternative application for cow dung waste resources in the automotive components field.

Co-production of amino acid-rich xylooligosaccharide and single-cell protein from paper mulberry by autohydrolysis and fermentation technologies

Background

Autohydrolysis is an extensively investigated pretreatment method due to its environmental friendliness. During autohydrolysis, most xylan from hemicellulose can be converted into xylooligosaccharides (XOS), and cellulose in the autohydrolyzed residues can be transformed into glucose after enzymatic hydrolysis. Both of these are value-added biochemicals in the biorefining process. In this work, paper mulberry (PM), which contains abundant protein, was utilized as a raw material to coproduce XOS and single-cell protein (SCP) through autohydrolysis and fermentation technologies.

Results

The results showed that 8.3 g of XOS and 1.8 g of amino acids could be recovered in the autohydrolysate (based on 100 g raw material) after autohydrolysis (170 °C, 1 h). Moreover, 5.7 g of low-DP XOS along with 1.8 g of amino acids could be further obtained from the autohydrolysate after hydrolysis with endo-β-1-4-xylanase. In addition, 20.1 g of fermentable monosaccharides was recovered after hydrolyzing the autohydrolyzed PM with cellulase, which can be used to produce 4.8 g of SCP after fermentation with Candida utilis.

Conclusion

As a valuable application of PM, a novel process is proposed to coproduce amino acid-rich XOS and SCP through autohydrolysis. The carbohydrate of PM is effectively converted to high value-added products.

Integrating enzymatic hydrolysis into subcritical water pretreatment optimization for bioethanol production from wheat straw

The conversion of lignocellulosic biomass to bioethanol is a potential approach to alleviate the energy crisis and environmental deterioration. To improve the conversion efficiency of bioethanol from wheat straw (WS), the optimization of subcritical water pretreatment and high solid hydrolysis were investigated in this study. Response surface methodology (RSM) accompanied with glucose concentration after enzymatic hydrolysis as a more reasonable response value was applied for the pretreatment optimization, and the optimum conditions were obtained as 220.51 °C of extraction temperature, 22.01 min of extraction time and 2.50% (w/v) of substrate loading. After pretreatment, the hemicellulose decreased by 18.37%, and the cellulose and lignin increased by 25.92% and 8.81%, respectively, which were consistent with the destroyed microstructure and raised crystallinity. The high efficiency of separate hydrolysis and fermentation (SHF) was verified by five commercial cellulases, and yields of hydrolysis and fermentation were 77.85-89.59% and 93.34-96.18%, respectively. Based on the high solid (15%) hydrolysis and fermentation, the ethanol concentration was significantly improved to 37.00 g/L. Interestingly, 64.47% of lignin was accumulated in the solid residue after enzymatic hydrolysis and it did not affect the efficiency of SHF, which further suggested that subcritical water mainly affected the structure of WS rather than the removal of lignin. Therefore, subcritical water pretreatment combined with high solid hydrolysis is a more effective solution for bioethanol conversion, which is also a promising strategy to utilize all components of lignocellulosic biomass.

Comprehensive analysis of important parameters of choline chloride-based deep eutectic solvent pretreatment of lignocellulosic biomass

Choline chloride based deep eutectic solvents have showed great potential in lignocellulosic biomass pretreatment. In this study, for DES pretreatment with different hydrogen bond donners of different raw materials under different reaction conditions, multivariate analysis methods including principal component analysis and partial least squares analysis were used for reveal the pretreatment mechanism by evaluating the inner relationships among 42 key process factors. Furthermore, based on molecular simulation, the detailed relationships between key variables were further analyzed. Meanwhile, four-dimensional color graphs were used to intuitively reveal the synergistic influence of multivariate conditions variables on pretreatment effect to obtain better economic benefits and energy consumption indicators for DES pretreatment. The results showed that HBD hydrophilic ability, HBD polarity, HBD acidity, HBD ability to form hydrogen bonds, molar ratio of HBD to choline chloride and pretreatment severity had great influence on the Choline chloride based deep eutectic solvents pretreatment effect.

Key process parameters for deep eutectic solvents pretreatment of lignocellulosic biomass materials: A review

Deep eutectic solvent (DES) has been considered as a novel green solvent for lignocellulosic biomass pretreatment. The efficiency of DES pretreatment is affected by the synergy of various process parameters. The study of effect of DES physicochemical properties and pretreatment reaction conditions on the mechanism of lignocellulose biomass fractionation was of great significance for the development of biomass conversion. Form the view of process control, this review summarized recent advances in DES pretreatment, analyzed the challenges, and prospected the future development of this research field.

Effect of severity factor on the hydrothermal pretreatment of sugarcane straw

The recalcitrant structures of sugarcane straw and related lignocellulosic biomasses require a pretreatment step to enable a better enzymatic attack during the hydrolysis. Factors like the energy consumption and the formation of inhibitors require the optimization of the pretreatment step. Thus, the influence of different severity factors (SF) on hydrothermal (also called liquid hot water, LHW) pretreatment was evaluated using a factorial design 2² with central point. The obtained results showed that low values of SF (<3.39) did not promote reasonable alteration in the sugarcane straw structures, whereas high SF values (>4.70) resulted in loss of hydrolyzed sugars, generation of inhibitors such as furfural, and formation of pseudo-lignin structures, despite high hemicellulose removal (∼97%). The residence time exhibited low influence on LHW. An optimum condition was found for the process (10 min and 195 °C) with low cellulose solubilization (9.80%) and a reasonable hemicellulose removal (85.45%).

The Influence of Residence Time during Hydrothermal Carbonisation of Miscanthus on Bio-Coal Combustion Chemistry

Miscanthus was treated by hydrothermal carbonisation in a 2-L batch reactor at 200 °C and 250 °C with residence times ranging between 0 and 24 h to understand the impact of residence time has on the resulting bio-coal combustion chemistry. Increasing the residence time results in dehydration of the bio-coal and increased repolymerisation; however, temperature has the greatest influence on bio-coal properties. After 24 h at 200 °C, bio-coal has similar properties to that of the 250 °C + 0 h bio-coal. After 1 h at 250 °C, the cellulose present in the raw biomass appears to be largely removed. The removal of cellulose and the associated dehydration and repolymerisation results in bio-coal having a ‘coal like’ combustion profile, which exhibits a decreasing reactivity with increasing residence time. At 200 °C + 0 h, 75% of the alkali metal is removed, increasing to 86% with increasing residence time. Further extraction is seen at 250 °C. Phosphorus and sulphur appear to undergo substantial extraction at 200 °C + 0 h but then are reincorporated with increasing residence time. The calcium content increases in the bio-coal with increasing residence time at 200 °C but then reduces after 1 h at 250 °C. Increasing temperature and residence time has been shown to decrease the fuels’ fouling and slagging propensity.

Astaxanthin stability and color change of krill during subcritical water treatment

Pacific krill (Euphausia pacifica) contains high amounts of astaxanthin, a carotenoid pigment with strong antioxidative activities. In this study, the effects of subcritical water temperatures (100-180 °C) and times (0-10 min) on color changes (L*, a*, and b*) and astaxanthin degradation in Pacific krill were investigated. In addition, an aqueous solution of pure astaxanthin and that of crude astaxanthin from Pacific krill, both at a concentration of 5 mg/L, were subjected to treatment under subcritical water conditions using a flow-type reactor to compare the degradation of free astaxanthin and astaxanthin fatty acid esters. To compare the results of the different treatment conditions on the properties of astaxanthin, the severity factor (log R₀) was calculated, which ranged from 0.38 to 3.52. The extractability of astaxanthin enhanced when the subcritical water treatment was carried out at log R₀ values of 2.00-2.44. In contrast, astaxanthin underwent 50% degradation at log R₀ > 2.44. The changes in the a* values correlated well with the astaxanthin content in the treated krill, while the b* and L* values might relate to the browning components forming owing to Maillard reaction. The results show that free astaxanthin was less stable than crude astaxanthin under subcritical water treatment.

Optimization of organosolv pretreatment of rice straw for enhanced biohydrogen production using Enterobacter aerogenes

Ethanol organosolv pretreated rice straw was used to produce biohydrogen using Enterobacter aerogenes. The effect of temperature (120-180°C), residence time (30-90min), and ethanol concentration (45-75%v/v) on the hydrogen yield, residual biomass, and lignin recovery was investigated using RSM. In contrast to the residual solid and lignin recovery, no considerable trend could be observed for the changes in the hydrogen yield at different treatment severities. The maximum hydrogen yield of 19.73mlg^-1 straw was obtained at the ethanol concentration of 45%v/v and 180°C for 30min. Furthermore, the potential amount of biohydrogen was estimated in the top ten rice producing nations using the experimental results. Approximately 355.8kt of hydrogen and 11.3Mt of lignin could globally be produced. Based on a Monte Carlo analysis, the production of biohydrogen from rice straw has the lowest risk in China and the highest in Japan.

Hydrolysis kinetics of tulip tree xylan in hot compressed water

Lignocellulosic biomass, a promising renewable resource, can be converted into numerous valuable chemicals post enzymatic saccharification. However, the efficacy of enzymatic saccharification of lignocellulosic biomass is low; therefore, pretreatment is necessary to improve the efficiency. Here, a kinetic analysis was carried out on xylan hydrolysis, after hot compressed water pretreatment of the lignocellulosic biomass conducted at 180-220°C for 5-30min, and on subsequent xylooligosaccharide hydrolysis. The weight ratio of fast-reacting xylan to slow-reacting xylan was 5.25 in tulip tree. Our kinetic results were applied to three different reaction systems to improve the pretreatment efficiency. We found that semi-continuous reactor is promising. Lower reaction temperatures and shorter space times in semi-continuous reactor are recommended for improving xylan conversion and xylooligosaccharide yield. In the theoretical calculation, 95% of xylooligosaccharide yield and xylan conversion were achieved simultaneously with high selectivity (desired product/undesired product) of 100 or more.