Enzymatic hydrolysis of autohydrolyzed barley husks

BACKGROUND: Barley husks were subjected to non‐isothermal autohydrolysis of different severities, yielding a liquid phase rich in hemicellulose‐derived compounds and a solid phase, composed mainly of cellulose and lignin. This solid phase was subjected to enzymatic hydrolysis in order to assess the effects of severity on the susceptibility of substrates to enzymatic hydrolysis. The effects of the liquid to solid ratio (LSR, in the range 6 to 18 g g^?1) and cellulase to substrate ratio (CSR, in the range 3.3 to 8.2 FPU g^?1) on the enzymatic hydrolysis were assessed. RESULTS: Up to 25.8 g oligomers per 100 g raw material were present in liquors from the hydrothermal processing. Enzymatic hydrolysis of solid phases obtained under selected conditions (log Ro = 4.14, LSR = 6 g g^?1 and CSR = 5.8 FPU g^?1) yielded glucose concentrations up to 67 g L^?1 (corresponding to cellulose to glucose conversions close to 100%). CONCLUSION: It was shown that autohydrolysis is an effective method for improving the enzymatic susceptibility of barley husks. High cellulose conversions resulting in high glucose yields were achieved by enzymatic hydrolysis at low LSR and CSR. The liquid fraction obtained upon autohydrolysis contained large amounts of hemicellulose‐derived compounds. Copyright © 2010 Society of Chemical Industry     

Manufacture of fibrous reinforcements for biodegradable biocomposites from Citysus scoparius

BACKGROUND: Cytisus scoparius samples were processed with hot, compressed water (autohydrolysis treatments) to obtain both fiber‐containing solids (suitable as reinforcements for composites) and a liquid phase containing sugar oligomers derived from hemicelluloses. The solid phase from autohydrolysis, mainly made up of cellulose and lignin, was employed for manufacturing polylactic acid (PLA)‐based biodegradable composites. The mechanical properties, water uptake and thermal properties of composites were assessed. RESULTS: The hydrolysis of the major hemicellulose polysaccharide components of Cytisus scoparius was interpreted using kinetic models based on sequential pseudo‐homogeneous first‐order, irreversible reactions. Operating under non‐isothermal conditions, the autohydrolysis experiment carried out at up to 215 °C led to the maximum concentration of sugar oligomers (accounting for about 71% of the initial xylan). These compounds can be employed for a variety of purposes, including applications as prebiotics. Composites containing autohydrolyzed fibers presented both improved impact strength and reduced water absorption ability. CONCLUSIONS: Autohydrolysis of Cytisus scoparius led to a liquid phase containing xylooligosacharides with commercial value, and to a solid phase suitable as a reinforcement for PLA‐based composites with reduced water retention ability. Copyright © 2010 Society of Chemical Industry     

Hydrothermal pretreatment for deconstruction of plant cell wall: Part II. Effect on cellulose structure and bioconversion

Influences of both ultrastructural modification of cellulose after hydrothermal pretreatment and products derived from lignin‐carbohydrate complex (LCC) on the subsequent enzymatic digestibility and fermentation were studied in this study. Under hydrothermal conditions, it was found that the rearrangement of hydrogen bonding pattern in cellulose via allomorph and conformational changes which was mainly severity‐dependent increased the numbers of water‐exposed glycosidic bond and the formation of “amorphous‐like” cellulose fibril facilitated enzymatic hydrolysis. Pseudo lignin, soluble xylo‐oligomers, phenols and degradation products from high severity impeded enzymatic digestion. LCC and phenols which were rich in pH‐controlled prehydrolyzate did not sufficiently inhibit yeast while furans and some aromatics which were rich in high‐severity prehydrolyzate might be potential inhibitors. Trade‐off phenomenon was solved by pH‐controlled operation and high yields in both glucose (83–93%) and xylose (75–80%) were simultaneously obtained. The final ethanol yield from cellulose to ethanol reached as high as 84–93%. © 2018 American Institute of Chemical Engineers AIChE J, 64: 1954–1964, 2018     

Mild autohydrolysis: an environmentally friendly technology for xylooligosaccharide production from wood

Eucalyptus globulus wood samples were subjected to hydrothermal treatments under mild operational conditions (145–190 ° C, liquor to solid ratio 6–10 g g⁻¹, reaction times up to 7.5 h). Residual xylan, xylooligosaccharides, other sugars, furfural, glucan and lignin contents were determined. Negligible effects were caused by hydrothermal treatments on both cellulose and lignin. Kinetic models were developed which describe the hydrolysis of hemicelluloses. Xylan degradation, xylooligosaccharide and xylose generation, and xylose dehydration to furfural were accurately described by models based on pseudohomogeneous, first‐order kinetics with Arrhenius‐type temperature dependence. These models are useful for a technical evaluation of this environmentally friendly technology. © 1999 Society of Chemical Industry     

Pilot‐plant production of xylo‐oligosaccharides from corncob by steaming,enzymatic hydrolysis and nanofiltration

This paper reports a pilot‐plant production process for xylo‐oligosaccharides (mainly xylobiose and xylotriose) from corncob meal by steaming treatment followed by enzymatic hydrolysis and nanofiltration. The effects of corncob meal pretreatment, steaming temperature and time were investigated in order to obtain maximum extraction of xylan and to minimize the autohydrolysis of xylan into xylose. The enzymatic reaction was carried out using Aspergillus niger AN‐1.15 endo‐xylanase at 55 °C and the optimum enzymatic hydrolysis time was 5 h. The conventional downstream processing for purification of xylo‐oligosaccharides was incorporated with nanofiltration technology, giving benefits of energy saving and removal of monosaccharides. The final product from 40 kg of corncob meal was 10 dm³ of xylo‐oligosaccharide syrup (800 g dm^?3 total sugar), containing 74.5% xylobiose and xylotriose. Copyright © 2004 Society of Chemical Industry     

Enzymatic production of Xylooligosaccharide from selected agricultural wastes

Four different agricultural wastes, namely tobacco stalk (TS), cotton stalk (CS), sunflower stalk (SS) and wheat straw (WS) were tested for the production of Xylooligosaccharide (XO). XO production was performed by enzymatic hydrolysis of xylans which were obtained by alkali extraction from the agricultural wastes. Depending on the source, it was found that these four agricultural wastes contained different amount of xylan, cellulose and lignin and the xylan obtained from these source contained different amount of sugar and uronic acid. The highest amount of arabinose was in xylan from WS while the other xylans mainly had xylose and small amount of glucose. Different xylanase preparations were evaluated for production XO from these xylan sources. Aspergillus niger xylanase produced lower amount of XO from wheat straw xylan (WSX) than cotton stalk xylan (CSX), sun flower xylan (SSX) and tobacco stalk xylan (TSX) while Trichoderma longibrachiatum xylanase hydrolyzed highly branched WSX better. The HPLC analysis of the hydrolysis products indicated that depending on structure and composition of xylan, A. niger xylanase produced less amount of xylose than T. longibrachiatum xylanase, and the hyrolysis product of A. niger xylanase contained different amount of oligosaccharides (X2 > X3 > X4 > X5 > X6, >X6). Regardless of the structural differences of the xylan types presented in this paper, all xylans generated XO with different degree of polymerization (DP), but the DP of XO depended on the enzyme specificity and the structure of substrate.     

Reaction mechanisms and kinetics of xylo‐oligosaccharide hydrolysis by dicarboxylic acids

Hydrothermal pretreatment of lignocellulosic materials generates a liquid stream rich in pentose sugar oligomers. Cost‐effective hydrolysis and utilization of these soluble sugar oligomers is an integral process of biofuel production. We report integrated rate equations for hydrolysis of xylo‐oligomers derived from pretreated hardwood by dicarboxylic maleic and oxalic acids. The highest xylose yield observed with dicarboxylic acids was 96%, and compared to sulfuric acid, was 5–15% higher with less xylose degradation. Dicarboxylic acids showed an inverse correlation between xylose degradation rates and acid loadings unlike sulfuric acid for which less acid results in less xylose degradation to aldehydes and humic substances. A combination of high acid and low‐temperature leads to xylose yield improvement. Hydrolysis time course data at three different acid concentrations and three temperatures between 140 and 180°C were used to develop a reaction model for the hydrolysis of xylo‐oligosaccharides to xylose by dicarboxylic acids. © 2012 American Institute of Chemical Engineers AIChE J, 59: 188–199, 2013     

Hydrothermal pretreatment for deconstruction of plant cell wall: Part I. Effect on lignin‐carbohydrate complex

Hydrothermal pretreatment with characteristic of green chemistry is considered as promising technology in the biorefineries. Using material balance and multiscale characterization techniques, the effects of process severity factor and pH on chemical behaviors of lignin‐carbohydrate complex (LCC) were systematically studied. During pretreatment, spatial relocation of lignin with covalently linked xylan facilitated local cell wall collapse. A kinetic model was established to describe the behaviors of LCC components changing with severity factor. It was found that cleavage of LCC linkage was strongly pH‐dependent. Low pH dominated cleavage of coumarate/ferulate esters which cross‐linking lignin with xylan and repolymerization of aromatics either from furfural or lignin into polymers such as pseudo lignin, while high pH which allowed the existence of soluble LCC dominated the aldol condensations from xylose to aromatics and depolymerizaton of lignin to phenols. Detailed reaction pathways concerned with LCC were finally established to elucidate the underlying mechanism. © 2018 American Institute of Chemical Engineers AIChE J, 64: 1938–1953, 2018     

高温液态水中甜高粱渣半纤维素水解及其机理

为了回收甜高粱渣中的半纤维素衍生糖并了解其水解机理,在自行设计的Flowthrough反应器中对甜高粱渣进行了高温液态水水解,分别考察了不同反应温度和反应液流量下水解液中产物的生成情况。研究表明,相对葡萄糖和阿拉伯糖而言,木糖的生成受反应温度和反应液流量影响更大。温度高于195 ℃时糖降解加剧,总木糖浓度不断降低;低流量（5 ml?min-1）条件下生成的木糖不能被及时排出而进一步降解。通过产物分析可知,甜高粱渣半纤维素中含有典型的O-乙酰基-4-O-甲基葡萄糖醛酸基阿拉伯糖基木聚糖结构,木糖、葡萄糖、阿拉伯糖、各种低聚糖、乙酸和葡萄糖醛酸等是半纤维素水解的直接产物,糠醛和5-羟甲基糠醛等是糖类的降解产物, 甲酸等小分子酸是它们的进一步降解产物。     

Enhanced Xylooligosaccharides Yields and Enzymatic Hydrolyzability of Cellulose using Acetic Acid Catalysis of Poplar Sawdust

To increase the value and promote the utilization of woody processing residues, poplar sawdust was used to produce xylooligosaccharides (XOS) with polymerization degrees of 2–6 by acetic acid catalysis. This process is considered to be an environmental friendly process, and the remaining solid fraction was decomposed to fermentable sugars by enzymatic hydrolysis. Response surface methodology (RSM) was applied to determine the main factors affecting the yield of XOS. XOS production was optimal at 170?±?3?°C with a 6.5?±?1% acetic acid concentration and 27?±?2?min reaction time. These conditions produced a 36.0?±?0.8% XOS yield from xylan, similar to the predicted value from the model. Careful analysis of the kinetic profile of XOS revealed that xylobiose to xylohexaose were the main products. Detectable degraded chemicals accounted for 71.0% xylan during acidic hydrolysis. When using enzymatic hydrolysis at a cellulase loading of 20 FPU/g cellulose, a 51.0% yield was achieved, which represented an 80% increase relative to pretreated autohydrolysis (28.3%), and reached production yields similar to that of diluted sulfuric acid pretreatment.     

The hydrolysis of xylan by Cellulomonas preparations

Thin layer chromatography was demonstrated as an effective technique for observing the time course of hydrolysis of a substituted xylan (arabinoxylan) by crude preparations of Cellulomonas. The chromatograms revealed a sequential pattern of appearance of xylooligomers and arabinoxylooligomers, with early appearance of relatively large oligomers and subsequent accumulation of xylobiose and (to a lesser extent) xylose and arabinose. The pattern indicated that the dominant enzymic activity towards arabinoxylan is that of an endoxylanase.     

水热预处理竹子促进酶解的效果及其影响因素

采用间歇式水热预处理装置,研究了水热预处理用于竹子的酶解规律,探讨了不同温度、处理时间、纤维素酶添加量及原料种类对促进竹子酶解的效果及其影响。结果表明水热预处理能显著提升竹子的酶解率,在优化条件190℃、10 min水热预处理,添加15 FPU·(g葡聚糖)^-1纤维素酶,72 h葡聚糖与木聚糖酶解率分别为74.3%、54.0%,提高到原来的3.5倍和4.7倍。过高的预处理温度与过长的预处理时间都将导致木糖大量降解和部分葡萄糖降解,使单糖总量下降。纤维素酶的添加量从15 FPU·(g 葡聚糖)^-1提高到60 FPU·(g 葡聚糖)^-1,可使未作预处理和水热预处理竹子的总糖回收率分别提高21.5%和9.9%,其促进酶解的作用远低于预处理的效果,通过预处理增大酶的可及性是提高酶解率的关键。水热预处理对于生物质原料具有选择性,不同的竹子原料具有显著不同的效果。     

Valorization of residual woody biomass (Olea europaea trimmings) based on aqueous fractionation

BACKGROUND: Olive tree trimmings, a widely available agricultural residue lacking added value applications, were subjected to treatments with hot, compressed water under a variety of operational conditions. As a result of treatments, hemicelluloses were solubilized, and the treated solids were enriched in cellulose and lignin. Spent solids from autohydrolysis were assayed as substrates for enzymatic hydrolysis and for bioethanol production by simultaneous saccharification and fermentation. RESULTS: Liquors from the aqueous fractionation stage resulted in the formation of soluble hemicellulose‐derived saccharides (mainly of oligomeric nature) at yields up to 26.2 g per 100 g oven‐dry raw material. Enzymatic hydrolysis of spent solids from the aqueous fractionation step led to solutions containing up to 58.8 g glucose L^?1 (corresponding to cellulose to glucose conversions up to 83.2%). Simultaneous saccharification and fermentation assays using spent solids as substrates enabled the production of media containing up to 38.2 g ethanol L^?1, corresponding to 72% of the stoichiometric amount. CONCLUSION: Aqueous (or hydrothermal) processing is a technology enabling the recovery of hemicelluloses (as soluble saccharides) and the production of spent solids with high susceptibility to enzymatic hydrolysis (suitable for bioethanol production by simultaneous saccharification and fermentation). Copyright © 2011 Society of Chemical Industry     

Effect of Xylanase and Dosage on the Refining Properties of Unbleached Softwood Kraft Pulp

Abstract

Two xylanase preparations were compared at different doses for their abilities to enhance the refining properties of a never-dried, unbleached kraft pulp derived from radiata pine. These enzymes varied in their ability to solubilise xylan from pulp, and the selective removal of pulp xylan did not reduce intrinsic fibre strength. At low levels of xylan solubilisation, there were increases in sheet densification after PFI refining without change in tensile and tear strength at a given sheet density, indicating lower pulp refining requirements. At high levels of xylan solubilisation, the level of sheet densification was greater but there was a small decrease in tensile strength at a given sheet density and an increase in tear strength. One of the xylanases yielded a selective increase in tear strength at a given tensile strength.     

Hemicelluloses obtaining from rapeseed cake residue generated in the biodiesel production process

The processing of rapeseed oil seeds for biodiesel production generates huge amounts of lignocellulosic cake residue mainly composed by cellulose, hemicelluloses and lignin. In this work, the valorisation of these components, especifically the majoritary fraction, hemicelluloses, was studied. Hemicelluloses were extracted, purified and characterized by different techniques (FTIR, ¹H NMR, ¹³C NMR, and GPC). Autohydrolysis and acid hydrolysis processes were applied to obtain sugar monomers and oligomers. Glucose and xylose were the main simple sugars in the obtained hydrolysates, representing 22.7% and 40.2% of total sugars content in the autohydrolysis hydrolysates and 27.7% and 36.6% in the acid hydrolysates respectively. Arabinose, galactose and mannose were present in relatively minor quantities.     

Production and in vitro evaluation of xylooligosaccharides generated from corn cobs

Corn cobs are major byproduct of maize processing industries. For value addition of maize byproducts, the present paper aims at extracting xylan from corn cobs and subsequent production of xylooligosaccharides (XOS). Compositional determination of corn cobs revealed 38.78% hemicellulose, 27.71% cellulose and 9.4% lignin. Recovery of xylan increased with increasing concentration of alkali during extraction. The extracted xylan was subjected to acidic hydrolysis to yield XOS. HPLC analysis of hydrolysate revealed increased production of XOS with time, but prolonged incubation resulted in higher amount of xylose. Four probiotic strains were used for undertaking in vitro evaluation of the prebiotic efficacy of XOS. XOS ensured higher growth rate for Enterococcus faecium as compared to other probionts, while fructooligosaccharides (FOS) supported higher proliferation of Lactobacillus viridiscens. This method of xylan extraction and production of XOS offers scope for value addition to the corn byproducts.     

Pretreatment of lignocellulosic biomass by autohydrolysis and aqueous ammonia percolation

A two-stage biomass pretreatment process-a combination of autohydrolysis and aqueous ammonia percolation-was experimentally studied as a method to remove and recover hemicellulose from lignocellulosic biomass. Hemicellulose was completely separated from the biomass after 1 hr of autohydrolysis at 200‡C. As reaction temperature and/or time of autohydrolysis was increased in the range of 170-200‡C and 1–2.5 hr, respectively, the amount of hemicellulose solubilization was increased ; however, more sugars were decomposed. Most of the extracted hemicellulose was recovered as xylose oligomer. Hemicellulose was found to inhibit the enzymatic hydrolysis of cellulose. When the biomass was consecutively pretreated with pure water at 180‡C for 30 min and with 10 wt% ammonia solution at 180‡C for 30 min, about 62% of the hemicellulose was extracted. The enzymatic digestibility of the pretreated biomass was as high as 95 %.     

碳源对平菇选择性降解稻草木素及其后续酶解性能的影响

前期研究发现,平菇预处理稻草表现出比较好的脱木素选择性和纤维素酶水解效果。为了使预处理后的稻草在纤维素酶水解过程中得到更多的单糖,通过向平菇预处理稻草固体培养基中添加麸皮、玉米皮和木聚糖,研究外加碳源对平菇降解稻草木素的选择性及后续酶水解效果的影响。结果表明,添加适量的麸皮和木聚糖可提高平菇处理稻草的脱木素选择性。麸皮和木聚糖添加量为稻草粉的10%时,脱木素选择系数分别由对照的1.86增加至2.58和2.03;预处理样品酶解后原料中总糖的46.8%和45.9%转化为可发酵单糖,分别比对照的35.5%提高了30%和28%。添加玉米皮对平菇预处理酶解效果影响相对较小,添加量为5%时,预处理样品酶解后总糖转化率仅比对照提高15%,增加添加量酶解总糖转化率反而低于对照样品。     

Effectiveness of antioxidants on lipid oxidation and lipid hydrolysis of cod liver oil

The capacity of the natural antioxidant from barley husks to retard oxidation of PUFA in cod liver oil (Gadus morhua) was investigated and compared to synthetic antioxidants. The results confirm the efficacy of a natural antioxidant derived from barley husks to slow down the progress of lipid hydrolysis and increase oxidative stability in cod liver oil. The rates of lipid hydrolysis and lipid oxidation were slowed down with increasing concentration of natural antioxidant used. Using 100 mg of the natural antioxidant was more effective than some synthetic antioxidants (BHA 200 mg and BHT 200 mg) against primary and secondary oxidation. The use of propyl gallate (PG) as an antioxidant (200 mg/kg in cod liver oil) was the most effective antioxidant employed in reducing the production of primary and delaying secondary oxidation products. The formation of free fatty acids (FFA) was significantly lower in samples with natural antioxidant (BE200 and BE100) than in the control samples. BHA and BHT were the most effective antioxidants employed to delay the lipid hydrolysis. Practical applications: The use of barley husks, which are residues of the brewing process, was optimized to obtain a crude antioxidant extract. Natural extracts of phenolic compounds with high antioxidant activity were obtained after prehydrolysis and delignification of barley husks. The raw extracts show more than two‐fold antioxidant capacity compared to BHT in terms of EC50. The results demonstrate the efficacy of a natural antioxidant derived from barley husks. The extract could be used in fatty foods (such as butter, oil, etc.) to prevent rancidity.