Characterization of oligomeric xylan structures from corn fiber resistant to pretreatment and simultaneous saccharification and fermentation

Lignin, extractives and structural carbohydrate characteristics of Thinopyrum intermedium biomass reveal additional valorization opportunities for dual-crop utilization

BACKGROUND

Thinopyrum intermedium (Host) Barkworth & D.R. Dewey, or intermediate wheat grass (IWG), is being developed as the first widely-available perennial grain candidate. However, because the crop is still in development, grain yields are lower than those of traditional cereals. Utilization of its non-grain biomass (e.g. for biofuel production and as a source of fine chemicals) would increase the economic value of its cultivation. The present study provides a structural characterization of the lignin and cell wall carbohydrates in IWG biomass and qualitative profiling of biomass extractives and compares them to those of annual wheat (Triticum aestivum) biomass grown in the same location and growing season.

RESULTS

The monosaccharide composition and ester-linked phenolic acid contents of vegetative biomass material from annual wheat and IWG were similar. IWG vegetative biomass is rich in feruloylated arabinoxylans (AX) with a very low substitution rate, whereas the AX from IWG bran have a slightly higher substitution rate. The structure of IWG lignin was investigated using both the quantitative derivatization followed by reductive cleavage method and 2D-NMR analysis, revealing an H:G:S lignin that incorporates tricin and is acylated with coumaric acid and smaller amounts of ferulates. IWG and wheat extractives contained fatty acids, various free phenolic compounds (tricin, monolignols and phenolic acids), phenolic conjugates and phytosterols.

CONCLUSION

The present study provides firm support for the further exploration of T. intermedium biomass as a carbohydrate feedstock (e.g, abundant in lightly substituted AX and cellulose polymers) for biofuel production and source of high-value fine chemicals, such as tricin. © 2024 Society of Chemical Industry.

The action of endo-xylanase and endo-glucanase on cereal cell wall polysaccharides and its implications for starch digestion kinetics in an in vitro poultry model

Endo-xylanase and endo-glucanase are supplemented to poultry diets in order to improve nutrient digestion and non-starch polysaccharide (NSP) fermentation. Here, the action of these enzymes on alcohol insoluble solids (AIS) from wheat and maize grains as well as its implications for starch digestion in milled grains were evaluated in vitro, under conditions mimicking the poultry digestive tract. For wheat AIS, GH11 endo-xylanase depolymerized soluble arabinoxylan (AX) during the gizzard phase, and proceeded to release insoluble AX under small intestine conditions. At the end of the in vitro digestion (480 min), the endo-xylanase, combined with a GH7 endo-β-1,4-glucanase, released 30.5 % of total AX and 18.1 % of total glucan in the form of arabinoxylo- and gluco-oligosaccharides, as detected by HPAEC-PAD and MALDI-TOF-MS. For maize AIS, the combined enzyme action released 2.2 % and 7.0 % of total AX and glucan, respectively. Analogous in vitro digestion experiments of whole grains demonstrated that the enzymatic release of oligomers coincided with altered grain microstructure, as examined by SEM. In the present study, cell wall hydrolysis did not affect in vitro starch digestion kinetics for cereal grains. This study contributes to understanding the action of feed enzymes on cereal NSP under conditions mimicking the poultry digestive tract.

Intensification of corn fiber saccharification using a tailor made enzymatic cocktail

The transition from an economic model based on resource extraction to a more sustainable and circular economy requires the development of innovative methods to unlock the potential of raw materials such as lignocellulosic biomasses. Corn fiber differs from more traditional lignocellulosic biomasses due to its high starch content, which provides additional carbohydrates for fermentation-based biomanufacturing processes. Due to its unique chemical composition, this study focused on the development of a tailor made enzymatic cocktail for corn fiber saccharification into monosaccharides. Three commercially available hydrolytic enzymes (Cellic® CTec2, Pentopan® Mono BG, and Termamyl® 300 L) were combined to hydrolyze the polysaccharide structure of the three main carbohydrate fractions of corn fiber (cellulose, hemicellulose and starch, respectively). Prior to saccharification, corn fiber was submitted to a mild hydrothermal pretreatment (30 min at 100 °C). Then, two experimental designs were used to render an enzymatic cocktail capable of providing efficient release of monosaccharides. Using 60 FPU/g DM of Cellic® CTec2 and 4.62 U/g DM of Termamyl® 300 L, without addition of Pentopan® Mono BG, resulted in the highest efficiencies for glucose and xylose release (66% and 30%, respectively). While higher enzyme dosages could enhance the saccharification efficiency, adding more enzymes would have a more pronounced effect on the overall process costs rather than in increasing the efficiency for monosaccharides release. The results revealed that the recalcitrance of corn fiber poses a problem for its full enzymatic degradation. This fact combined with the unique chemical composition of this material, justify the need for developing a tailor made enzymatic cocktail for its degradation. However, attention should also be given to the pretreatment step to reduce even more the recalcitrance of corn fiber and improve the performance of the tailored cocktail, as a consequence.

Ferulic and coumaric acid in corn and soybean meal-based diets and in feces from pigs fed these diets

BACKGROUND

Arabinoxylan is the main fiber component in corn and corn co-products that are commonly included in pig diets. However, this fiber fraction is resistant to enzymatic degradation in the gastrointestinal tract of pigs. Ferulic acid and p-coumaric acid are covalently linked to arabinoxylan, so it is likely that the majority of these hydroxycinnamic acids are excreted in feces. However, data to confirm this have not been reported. The objective of this research was therefore to quantify the ferulic and p-coumaric acids in a diet based on corn and soybean meal (SBM) and in a diet based on corn, SBM, and distillers' dried grains with solubles, as well as in feces from pigs fed these diets.

RESULTS

The concentration of bound ferulic and coumaric acids in diets was greater in the corn-SBM-DDGS diet and in feces from pigs fed this diet than in the corn-SBM diet and feces from pigs fed that diet. The disappearance of free coumaric acids was greater (>85%) than that of bound phenolic acids (<50%) in both diets. The disappearance of free coumaric acid and bound ferulic acid in the intestinal tract of pigs was not different between the two diets. In contrast, disappearance of bound coumaric acid was greater (P < 0.05) in the corn-SBM diet than in the corn-SBM-DDGS diet.

CONCLUSION

A diet based on corn and SBM contains less hydroxycinnamic acid than a corn-SBM-DDGS diet but bound phenolic acids are more resistant to digestion by pigs than free phenolic acids. © 2023 Society of Chemical Industry.

Insights into the capability of the lignocellulolytic enzymes of Penicillium parvum 4-14 to saccharify corn bran after alkaline hydrogen peroxide pretreatment

BACKGROUND

Corn bran is a major agro-industrial byproduct from corn starch processing. It contains abundant arabinoxylan that can be converted into value-added chemicals via biotechnology. Corn bran arabinoxylan (CBAX) is one of the most recalcitrant xylans for enzymatic degradation due to its particular heterogeneous nature. The present study aimed to investigate the capability of the filamentous fungus Penicillium parvum 4-14 to enzymatically saccharify CBAX and reveal the fungal carbohydrate-active enzyme (CAZyme) repertoire by genome sequencing and secretome analysis.

RESULTS

CBAX1 and CBAX2 with different branching degrees, together with corn bran residue (CBR) were generated from corn bran after alkaline hydrogen peroxide (AHP) pretreatment and graded ethanol precipitation. The protein blends E_CBAX1, E_CBAX2, and E_CBR were produced by the fungus grown on CBAX1, CBAX2, or CBR, respectively. Under the optimal conditions, E_CBAX1 released more than 80% xylose and arabinose from CBAX1 and CBAX2. Almost complete saccharification of the arabinoxylans was achieved by combining E_CBAX1 and a commercial enzyme cocktail Cellic®CTec3. Approximately 89% glucose, 64% xylose, and 64% arabinose were liberated from CBR by E_CBR. The combination of E_CBR with Cellic®CTec3 enhanced the saccharification of CBR, with conversion ratios of 97% for glucose, 81% for xylose, and 76% for arabinose. A total of 376 CAZymes including plentiful lignocellulolytic enzymes were predicted in P. parvum based on the fungal genomic sequence (25.8 Mb). Proteomic analysis indicated that the expression of CAZymes in P. parvum varied between CBAX1 and CBR, and the fungus produced complete cellulases, numerous hemicellulases, as well as high levels of glycosidases under the culture conditions.

CONCLUSIONS

This investigation disclosed the CAZyme repertoire of P. parvum at the genomic and proteomic levels, and elaborated on the promising potential of fungal lignocellulolytic enzymes upon saccharification of corn bran biomass after AHP pretreatment.

Engineering of xylanases for the development of biotechnologically important characteristics

Xylanases are the main biocatalysts used for the reduction of the xylan backbone from hemicellulose, randomly splitting off β-1,4-glycosidic linkages between xylopyranosyl residues. Xylanase market has been annually estimated at 500 million US Dollars and they are potentially used in broad industrial process ranges such as paper pulp biobleaching, xylo-oligosaccharide production, and biofuel manufacture from lignocellulose. The highly stable xylanases are preferred in the downstream procedure of industrial processes because they can tolerate severe conditions. Almost all native xylanases can not endure adverse conditions thus they are industrially not proper to be utilized. Protein engineering is a powerful technology for developing xylanases, which can effectively work in adverse conditions and can meet requirements for industrial processes. This study considered state-of-the-art strategies of protein engineering for creating the xylanase gene diversity, high-throughput screening systems toward upgraded traits of the xylanases, and the prediction and comprehensive analysis of the target mutations in xylanases by in silico methods. Also, key molecular factors have been elucidated for industrial characteristics (alkaliphilic enhancement, thermal stability, and catalytic performance) of GH11 family xylanases. The present review explores industrial characteristics improved by directed evolution, rational design, and semi-rational design as protein engineering approaches for pulp bleaching process, xylooligosaccharides production, and biorefinery & bioenergy production.

Comparison of the Biochemical Properties and Roles in the Xyloglucan-Rich Biomass Degradation of a GH74 Xyloglucanase and Its CBM-Deleted Variant from Thielavia terrestris

Xyloglucan is closely associated with cellulose and still retained with some modification in pretreated lignocellulose; however, its influence on lignocellulose biodegradation is less understood. TtGH74 from Thielavia terrestris displayed much higher catalytic activity than previously characterized fungal GH74 xyloglucanases. The carbohydrate-binding module 1 (CBM1) deleted variant (TtGH74ΔCBM) had the same optimum temperature and pH but an elevated thermostability. TtGH74 displayed a high binding affinity on xyloglucan and cellulose, while TtGH74ΔCBM completely lost the adsorption capability on cellulose. Their hydrolysis action alone or in combination with other glycoside hydrolases on the free xyloglucan, xyloglucan-coated phosphoric acid-swollen cellulose or pretreated corn bran and apple pomace was compared. CBM1 might not be essential for the hydrolysis of free xyloglucan but still effective for the associated xyloglucan to an extent. TtGH74 alone or synergistically acting with the CBH1/EG1 mixture was more effective in the hydrolysis of xyloglucan in corn bran, while TtGH74ΔCBM showed relatively higher catalytic activity on apple pomace, indicating that the role and significance of CBM1 are substrate-specific. The degrees of synergy for TtGH74 or TtGH74ΔCBM with the CBH1/EG1 mixture reached 1.22–2.02. The addition of GH10 xylanase in TtGH74 or the TtGH74ΔCBM/CBH1/EG1 mixture further improved the overall hydrolysis efficiency, and the degrees of synergy were up to 1.50–2.16.

Cell Wall Composition Impacts Structural Characteristics of the Stems and Thereby the Biomass Yield

Maize stalks support leaves and reproductive structures and functionally support water and nutrient transport; besides, their anatomical and biochemical characteristics have been described as a plant defense against stress, also impacting economically important applications. In this study, we evaluated agronomical and stem description traits in a subset of maize inbred lines that showed variability for cell wall composition in the internodes. Overall, a great proportion of lignin subunit G and a low concentration of p-coumaric acid and lignin subunit S are beneficial for greater rind puncture resistance and taller plants, with a greater biomass yield. Also, the greater the proportions of subunit H, the longer the internode. Finally, the lower the total hemicellulose content, the greater the rind puncture resistance. Our results confirmed the effect of the cell wall on agronomic and stalk traits, which would be useful in applied breeding programs focused on biomass yield improvement.

Mass spectrometry imaging of oligosaccharides following in situ enzymatic treatment of maize kernels

In recent years enzymatic treatment of maize has been utilized in the wet-milling process to increase the yield of extracted starch, proteins, and other constituents. One of the strategies to obtain this goal is to add enzymes that break down insoluble cell-wall polysaccharides which would otherwise entrap starch granules. Due to the high complexity of maize polysaccharides, this goal is not easily achieved and more knowledge about the substrate and enzyme performances is needed. To gather information of both enzyme performance and increase substrate understanding, a method was developed using mass spectrometry imaging (MSI) to analyze degradation products from polysaccharides following enzymatic treatment of the maize endosperm. Different enzymes were spotted onto cryosections of maize kernels which had been pre-treated with an amylase to remove starch. The cryosections were then incubated for 17 h. before mass spectrometry images were generated with a MALDI-MSI setup. The images showed varying degradation products for the different enzymes observed as pentose oligosaccharides differing with regards to sidechains and the number of linked pentoses. The method proved suitable for identifying the reaction products formed after reaction with different xylanases and arabinofuranosidases and for characterization of the complex arabinoxylan substrate in the maize kernel. HYPOTHESES: Mass spectrometry imaging can be a useful analytical tool for obtaining information of polysaccharide constituents and enzyme performance from maize samples.

Elucidating the multifunctional role of the cell wall components in the maize exploitation

BACKGROUND

Besides the use of maize grain as food and feed, maize stover can be a profitable by-product for cellulosic ethanol production, whereas the whole plant can be used for silage production. However, yield is reduced by pest damages, stem corn borers being one of the most important yield constraints. Overall, cell wall composition is key in determining the quality of maize biomass, as well as pest resistance. This study aims to evaluate the composition of the four cell wall fractions (cellulose, hemicellulose, lignin and hydroxycinnamates) in diverse maize genotypes and to understand how this composition influences the resistance to pests, ethanol capacity and digestibility.

RESULTS

The following results can be highlighted: (i) pests' resistant materials may show cell walls with low p-coumaric acid and low hemicellulose content; (ii) inbred lines showing cell walls with high cellulose content and high diferulate cross-linking may present higher performance for ethanol production; (iii) and inbreds with enhanced digestibility may have cell walls poor in neutral detergent fibre and diferulates, combined with a lignin polymer composition richer in G subunits.

CONCLUSIONS

Results evidence that there is no maize cell wall ideotype among the tested for optimal performance for various uses, and maize plants should be specifically bred for each particular application.

Polysaccharide utilization loci-driven enzyme discovery reveals BD-FAE: a bifunctional feruloyl and acetyl xylan esterase active on complex natural xylans

BACKGROUND

Nowadays there is a strong trend towards a circular economy using lignocellulosic biowaste for the production of biofuels and other bio-based products. The use of enzymes at several stages of the production process (e.g., saccharification) can offer a sustainable route due to avoidance of harsh chemicals and high temperatures. For novel enzyme discovery, physically linked gene clusters targeting carbohydrate degradation in bacteria, polysaccharide utilization loci (PULs), are recognized 'treasure troves' in the era of exponentially growing numbers of sequenced genomes.

RESULTS

We determined the biochemical properties and structure of a protein of unknown function (PUF) encoded within PULs of metagenomes from beaver droppings and moose rumen enriched on poplar hydrolysate. The corresponding novel bifunctional carbohydrate esterase (CE), now named BD-FAE, displayed feruloyl esterase (FAE) and acetyl esterase activity on simple, synthetic substrates. Whereas acetyl xylan esterase (AcXE) activity was detected on acetylated glucuronoxylan from birchwood, only FAE activity was observed on acetylated and feruloylated xylooligosaccharides from corn fiber. The genomic contexts of 200 homologs of BD-FAE revealed that the 33 closest homologs appear in PULs likely involved in xylan breakdown, while the more distant homologs were found either in alginate-targeting PULs or else outside PUL contexts. Although the BD-FAE structure adopts a typical α/β-hydrolase fold with a catalytic triad (Ser-Asp-His), it is distinct from other biochemically characterized CEs.

CONCLUSIONS

The bifunctional CE, BD-FAE, represents a new candidate for biomass processing given its capacity to remove ferulic acid and acetic acid from natural corn and birchwood xylan substrates, respectively. Its detailed biochemical characterization and solved crystal structure add to the toolbox of enzymes for biomass valorization as well as structural information to inform the classification of new CEs.

Combinatorial Engineering of Transcriptional Activators in Penicillium oxalicum for Improved Production of Corn-Fiber-Degrading Enzymes

Enzymatic conversion of corn fiber to fermentable sugars is beneficial to improving the economic efficiency of corn processing. In this work, the filamentous fungus Penicillium oxalicum was found to secrete enzymes for efficient saccharification of un-pretreated corn fiber. Separate engineering of transcriptional activators ClrB, XlnR, and AraR led to enhanced production of different sets of lignocellulolytic enzymes. Particularly, the enzymes produced by XlnR- and AraR-engineered strains showed a synergistic effect in corn fiber saccharification. Combinatorial engineering of all three activators generated a strain MCAX with 3.1- to 51.0-fold increases in lignocellulolytic enzyme production compared with the parent strain. In addition, the enzymes of strain MCAX released significantly more fermentable sugars from corn fiber than those of the parent strain at the same protein dosage. The results suggest that this strain has potential for on-site production of enzymes for corn fiber saccharification.

Plant Glycan Metabolism by Bifidobacteria

Members of the genus Bifidobacterium, of which the majority have been isolated as gut commensals, are Gram-positive, non-motile, saccharolytic, non-sporulating, anaerobic bacteria. Many bifidobacterial strains are considered probiotic and therefore are thought to bestow health benefits upon their host. Bifidobacteria are highly abundant among the gut microbiota of healthy, full term, breast-fed infants, yet the relative average abundance of bifidobacteria tends to decrease as the human host ages. Because of the inverse correlation between bifidobacterial abundance/prevalence and health, there has been an increasing interest in maintaining, increasing or restoring bifidobacterial populations in the infant, adult and elderly gut. In order to colonize and persist in the gastrointestinal environment, bifidobacteria must be able to metabolise complex dietary and/or host-derived carbohydrates, and be resistant to various environmental challenges of the gut. This is not only important for the autochthonous bifidobacterial species colonising the gut, but also for allochthonous bifidobacteria provided as probiotic supplements in functional foods. For example, Bifidobacterium longum subsp. longum is a taxon associated with the metabolism of plant-derived poly/oligosaccharides in the adult diet, being capable of metabolising hemicellulose and various pectin-associated glycans. Many of these plant glycans are believed to stimulate the metabolism and growth of specific bifidobacterial species and are for this reason classified as prebiotics. In this review, bifidobacterial carbohydrate metabolism, with a focus on plant poly-/oligosaccharide degradation and uptake, as well as its associated regulation, will be discussed.

Debranching enzymes in corn/soybean meal-based poultry feeds: a review

This review discusses the complex nature of the primary nonstarch polysaccharide (NSP) in corn with respect to the merit of debranching enzymes. Celluloses, hemicelluloses, and pectins comprise the 3 major categories of NSP that make up nearly 90% of plant cell walls. Across cereals, the hemicellulose arabinoxylan exists as the primary NSP, followed by cellulose, glucans, and others. Differences in arabinoxylan structure among cereals and cereal fractions are facilitated by cereal type, degree and pattern of substitution along the xylan backbone, phenol content, and cross-linkages. In particular, arabinoxylan (also called glucuronoarabinoxylan) in corn is heavily fortified with substituents, being more populated than in wheat and other cereal grains. Feed-grade xylanases - almost solely of the glycoside hydrolase (GH) 10 and GH 11 families - require at least 2 or 3 contiguous xylose units to be free of attachments to effectively attack the xylan chain. This canopy of attachments, along with a high phenol content and the insoluble nature of corn glucuronoarabinoxylan, confers a significant resistance to xylanase attack. Both in vitro and in vivo studies demonstrate that debranching enzymes appreciably increase xylanase access and fiber degradability by removing these attachments and breaking phenolic linkages. The enzymatic degradation of the highly branched arabinoxylan can facilitate disassembly of other fibers by increasing exposure to pertinent carbohydrases. For cereals, the arabinofuranosidases, α-glucuronidases, and esterases are some of the more germane debranching enzymes. Enzyme composites beyond the simple core mixes of xylanases, cellulases, and glucanases can exploit synergistic benefits generated by this class of enzymes. A broad scope of enzymatic activity in customized mixes can more effectively target the resilient NSP construct of cereal grains in commercial poultry diets, particularly those in corn-based feeds.

Structural characterization of the family GH115 α-glucuronidase from Amphibacillus xylanus yields insight into its coordinated action with α-arabinofuranosidases

The coordinated action of carbohydrate-active enzymes has mainly been evaluated for the purpose of complete saccharification of plant biomass (lignocellulose) to sugars. By contrast, the coordinated action of accessory hemicellulases on xylan debranching and recovery is less well characterized. Here, the activity of two family GH115 α-glucuronidases (SdeAgu115A from Saccharophagus degradans, and AxyAgu115A from Amphibacillus xylanus) on spruce arabinoglucuronoxylan (AGX) was evaluated in combination with an α-arabinofuranosidase from families GH51 (AniAbf51A, aka E-AFASE from Aspergillus niger) and GH62 (SthAbf62A from Streptomyces thermoviolaceus). The α-arabinofuranosidases boosted (methyl)-glucuronic acid release by SdeAgu115A by approximately 50 % and 30 %, respectively. The impact of the α-arabinofuranosidases on AxyAgu115A activity was comparatively low, motivating its structural characterization. The crystal structure of AxyAgu115A revealed increased length and flexibility of the active site loop compared to SdeAgu115A. This structural difference could explain the ability of AxyAgu115A to accommodate more highly substituted arabinoglucuronoxylan, and inform enzyme selections for improved AGX recovery and use.

Wood hemicelluloses exert distinct biomechanical contributions to cellulose fibrillar networks

Hemicelluloses, a family of heterogeneous polysaccharides with complex molecular structures, constitute a fundamental component of lignocellulosic biomass. However, the contribution of each hemicellulose type to the mechanical properties of secondary plant cell walls remains elusive. Here we homogeneously incorporate different combinations of extracted and purified hemicelluloses (xylans and glucomannans) from softwood and hardwood species into self-assembled networks during cellulose biosynthesis in a bacterial model, without altering the morphology and the crystallinity of the cellulose bundles. These composite hydrogels can be therefore envisioned as models of secondary plant cell walls prior to lignification. The incorporated hemicelluloses exhibit both a rigid phase having close interactions with cellulose, together with a flexible phase contributing to the multiscale architecture of the bacterial cellulose hydrogels. The wood hemicelluloses exhibit distinct biomechanical contributions, with glucomannans increasing the elastic modulus in compression, and xylans contributing to a dramatic increase of the elongation at break under tension. These diverging effects cannot be explained solely from the nature of their direct interactions with cellulose, but can be related to the distinct molecular structure of wood xylans and mannans, the multiphase architecture of the hydrogels and the aggregative effects amongst hemicellulose-coated fibrils. Our study contributes to understanding the specific roles of wood xylans and glucomannans in the biomechanical integrity of secondary cell walls in tension and compression and has significance for the development of lignocellulosic materials with controlled assembly and tailored mechanical properties.

Hemicelluloses are an essential constituent of plant cell walls, but the individual biomechanical roles remain elusive. Here the authors report on the interaction of wood hemicellulose with bacterial cellulose during deposition and explore the resultant fibrillar architecture and mechanical properties.

Growth performance and nutrient digestibility of growing and finishing pigs fed multienzyme-supplemented low-energy and -amino acid diets

A study was conducted to determine the effects of supplementing corn-soybean meal-based diets with a multienzyme on growth performance, bone mineralization, apparent ileal digestibility (AID) and apparent total tract digestibility (ATTD) of nutrients of growing pigs. A total of 276 pigs (body weight [BW] = 33.99 ± 4.3 kg) were housed by sex in 45 pens of 6 or 7 pigs and fed 5 diets (9 pens/diet) in a randomized complete block design. Diets were positive control (PC); and negative control 1 (NC1) or negative control 2 (NC2) without or with multienzyme. The multienzyme used supplied at least 1,800, 1,244, 6,600, and 1,000 units of xylanase, β-glucanase, arabinofuranosidase, and phytase per kilogram of diet, respectively. The PC diet was adequate in all nutrients according to NRC recommendations and had greater digestible P content than NC1 or NC2 diet by 0.134 percentage points. The PC diet had greater net energy (NE) and standardized ileal digestible amino acids (AA) content than NC1 diet by 3%, and than NC2 diet by 5%. The diets were fed in 4 phases based on BW: Phase 1: 34-50 kg; Phase 2: 50-75 kg; Phase 3: 75-100 kg; and Phase 4: 100-120 kg. Nutrient digestibility and bone mineralization were determined at the end of Phase 1. Overall (34-120 kg BW), pigs fed the PC and NC1 diets did not differ in average daily gain (ADG) and average daily feed intake. Pigs fed NC2 diet had lower (P < 0.05) ADG and gain-to-feed ratio (G:F) than those fed PC diet. Pigs fed PC diet had greater (P < 0.05) bone ash content and ATTD of P than those fed NC1 diet. The ATTD of GE for PC diet was greater (P < 0.05) than that for NC2 diet, and tended to be greater (P < 0.10) than that for NC1 diet. Multienzyme interacted (P < 0.05) with negative control diet type on overall ADG and AID of GE such that multienzyme did not affect overall ADG and AID of GE for the NC1 diet, but increased (P < 0.05) overall ADG and AID of GE for NC2 diet by 5.09 and 8.74%, respectively. Multienzyme did not interact with negative control diet type on overall G:F, bone ash content, AID of AA, and ATTD of nutrients. Multienzyme increased (P < 0.05) overall G:F, AID of methionine, ATTD of GE and P, and tended to increase (P = 0.056) bone ash content. The ADG, bone ash content, and ATTD of GE and P for the multienzyme-supplemented diets were similar to (P > 0.10) PC diet. Thus, NE and digestible AA and P can be lowered by ≤5% in multienzyme-supplemented diets without effects on growth performance and bone ash of pigs.

Functional Validation of Two Fungal Subfamilies in Carbohydrate Esterase Family 1 by Biochemical Characterization of Esterases From Uncharacterized Branches

The fungal members of Carbohydrate Esterase family 1 (CE1) from the CAZy database include both acetyl xylan esterases (AXEs) and feruloyl esterases (FAEs). AXEs and FAEs are essential auxiliary enzymes to unlock the full potential of feedstock. They are being used in many biotechnology applications including food and feed, pulp and paper, and biomass valorization. AXEs catalyze the hydrolysis of acetyl group from xylan, while FAEs release ferulic and other hydroxycinnamic acids from xylan and pectin. Previously, we reported a phylogenetic analysis for the fungal members of CE1, establishing five subfamilies (CE1_SF1–SF5). Currently, the characterized AXEs are in the subfamily CE1_SF1, whereas CE1_SF2 contains mainly characterized FAEs. These two subfamilies are more related to each other than to the other subfamilies and are predicted to have evolved from a common ancestor, but target substrates with a different molecular structure. In this study, four ascomycete enzymes from CE1_SF1 and SF2 were heterologously produced in Pichia pastoris and characterized with respect to their biochemical properties and substrate preference toward different model and plant biomass substrates. The selected enzymes from CE1_SF1 only exhibited AXE activity, whereas the one from CE1_SF2 possessed dual FAE/AXE activity. This dual activity enzyme also showed broad substrate specificity toward model substrates for FAE activity and efficiently released both acetic acid and ferulic acid (∼50%) from wheat arabinoxylan and wheat bran which was pre-treated with a commercial xylanase. These fungal AXEs and FAEs also showed promising biochemical properties, e.g., high stability over a wide pH range and retaining more than 80% of their residual activity at pH 6.0–9.0. These newly characterized fungal AXEs and FAEs from CE1 have high potential for biotechnological applications. In particular as an additional ingredient for enzyme cocktails to remove the ester-linked decorations which enables access for the backbone degrading enzymes. Among these novel enzymes, the dual FAE/AXE activity enzyme also supports the evolutionary relationship of CE1_SF1 and SF2.

Feruloyl Esterases for Biorefineries: Subfamily Classified Specificity for Natural Substrates

Feruloyl esterases (FAEs) have an important role in the enzymatic conversion of lignocellulosic biomass by decoupling plant cell wall polysaccharides and lignin. Moreover, FAEs release anti-oxidative hydroxycinnamic acids (HCAs) from biomass. As a plethora of FAE candidates were found in fungal genomes, FAE classification related to substrate specificity is an indispensability for selection of most suitable candidates. Hence, linking distinct substrate specificities to a FAE classification, such as the recently classified FAE subfamilies (SF), is a promising approach to improve the application of these enzymes for a variety of industrial applications. In total, 14 FAEs that are classified members of SF1, 5, 6, 7, 9, and 13 were tested in this research. All FAEs were investigated for their activity toward a variety of substrates: synthetic model substrates, plant cell wall-derived substrates, including lignin, and natural substrates. Released HCAs were determined using reverse phase-ultra high performance liquid chromatography coupled to UV detection and mass spectrometry. Based on this study, FAEs of SF5 and SF7 showed the highest release of FA, pCA, and diFAs over the range of substrates, while FAEs of SF6 were comparable but less pronounced for diFAs release. These results suggest that SF5 and SF7 FAEs are promising enzymes for biorefinery applications, like the production of biofuels, where a complete degradation of the plant cell wall is desired. In contrast, SF6 FAEs might be of interest for industrial applications that require a high release of only FA and pCA, which are needed as precursors for the production of biochemicals. In contrast, FAEs of SF1, 9 and 13 showed an overall low release of HCAs from plant cell wall-derived and natural substrates. The obtained results substantiate the previous SF classification as a useful tool to predict the substrate specificity of FAEs, which eases the selection of FAE candidates for industrial applications.

Development of a thermophilic coculture for corn fiber conversion to ethanol

The fiber in corn kernels, currently unutilized in the corn to ethanol process, represents an opportunity for introduction of cellulose conversion technology. We report here that Clostridium thermocellum can solubilize over 90% of the carbohydrate in autoclaved corn fiber, including its hemicellulose component glucuronoarabinoxylan (GAX). However, Thermoanaerobacterium thermosaccharolyticum or several other described hemicellulose-fermenting thermophilic bacteria can only partially utilize this GAX. We describe the isolation of a previously undescribed organism, Herbinix spp. strain LL1355, from a thermophilic microbiome that can consume 85% of the recalcitrant GAX. We sequence its genome, and based on structural analysis of the GAX, identify six enzymes that hydrolyze GAX linkages. Combinations of up to four enzymes are successfully expressed in T. thermosaccharolyticum. Supplementation with these enzymes allows T. thermosaccharolyticum to consume 78% of the GAX compared to 53% by the parent strain and increases ethanol yield from corn fiber by 24%.

Corn fiber is a difficult feedstock to utilize due to its recalcitrant hemicellulose. Here, the authors characterize the recalcitrant structures, isolate a new bacterium to consume the hemicellulose, identify its enzymes, and show the benefit with increased conversion of corn fiber to ethanol.

Phenolic cross-links: building and de-constructing the plant cell wall

Covering: Up to 2019Phenolic cross-links and phenolic inter-unit linkages result from the oxidative coupling of two hydroxycinnamates or two molecules of tyrosine. Free dimers of hydroxycinnamates, lignans, play important roles in plant defence. Cross-linking of bound phenolics in the plant cell wall affects cell expansion, wall strength, digestibility, degradability, and pathogen resistance. Cross-links mediated by phenolic substituents are particularly important as they confer strength to the wall via the formation of new covalent bonds, and by excluding water from it. Four biopolymer classes are known to be involved in the formation of phenolic cross-links: lignins, extensins, glucuronoarabinoxylans, and side-chains of rhamnogalacturonan-I. Lignins and extensins are ubiquitous in streptophytes whereas aromatic substituents on xylan and pectic side-chains are commonly assumed to be particular features of Poales sensu lato and core Caryophyllales, respectively. Cross-linking of phenolic moieties proceeds via radical formation, is catalyzed by peroxidases and laccases, and involves monolignols, tyrosine in extensins, and ferulate esters on xylan and pectin. Ferulate substituents, on xylan in particular, are thought to be nucleation points for lignin polymerization and are, therefore, of paramount importance to wall architecture in grasses and for the development of technology for wall disassembly, e.g. for the use of grass biomass for production of 2^nd generation biofuels. This review summarizes current knowledge on the intra- and extracellular acylation of polysaccharides, and inter- and intra-molecular cross-linking of different constituents. Enzyme mediated lignan in vitro synthesis for pharmaceutical uses are covered as are industrial exploitation of mutant and transgenic approaches to control cell wall cross-linking.

Nativity of lignin carbohydrate bonds substantiated by biomimetic synthesis

The question of whether lignin is covalently linked to carbohydrates in native wood, forming what is referred to as lignin-carbohydrate complexes (LCCs), still lacks unequivocal proof. This is mainly due to the need to isolate lignin from woody materials prior to analysis, under conditions leading to partial chemical modification of the native wood polymers. Thus, the correlation between the structure of the isolated LCCs and LCCs in situ remains open. As a way to circumvent the problematic isolation, biomimicking lignin polymerization in vivo and in vitro is an interesting option. Herein, we report the detection of lignin-carbohydrate bonds in the extracellular lignin formed by tissue-cultured Norway spruce cells, and in modified biomimetic lignin synthesis (dehydrogenation polymers). Semi-quantitative 2D heteronuclear singular quantum coherence (HSQC)-, 31P -, and 13C-NMR spectroscopy were applied as analytical tools. Combining results from these systems, four types of lignin-carbohydrate bonds were detected; benzyl ether, benzyl ester, γ-ester, and phenyl glycoside linkages, providing direct evidence of lignin-carbohydrate bond formation in biomimicked lignin polymerization. Based on our findings, we propose a sequence for lignin-carbohydrate bond formation in plant cell walls.

Insight into the role of α-arabinofuranosidase in biomass hydrolysis: cellulose digestibility and inhibition by xylooligomers

BACKGROUND

α-l-Arabinofuranosidase (ARA), a debranching enzyme that can remove arabinose substituents from arabinoxylan and arabinoxylooligomers (AXOS), promotes the hydrolysis of the arabinoxylan fraction of biomass; however, the impact of ARA on the overall digestibility of cellulose is controversial. In this study, we investigated the effects of the addition of ARA on cellulase hydrolytic action.

RESULTS

We found that approximately 15% of the xylan was converted into AXOS during the hydrolysis of aqueous ammonia-pretreated corn stover and that this AXOS fraction was approximately 12% substituted with arabinose. The addition of ARA removes a portion of the arabinose decoration, but the resulting less-substituted AXOS inhibited cellulase action much more effectively; showing an increase of 45.7%. Kinetic experiments revealed that AXOS with a lower degree of arabinose substitution showed stronger affinity for the active site of cellobiohydrolase, which could be the mechanism of increased inhibition.

CONCLUSIONS

Our findings strongly suggest that the ratio of ARA and other xylanases should be carefully selected to avoid the strong inhibition caused by the less-substituted AXOS during the hydrolysis of arabinoxylan-containing biomass. This study advances our understanding of the inhibitory mechanism of xylooligomers and provides critical new insights into the relationship of ARA addition and cellulose digestibility.

Development of an oligosaccharide library to characterise the structural variation in glucuronoarabinoxylan in the cell walls of vegetative tissues in grasses

BACKGROUND

Grass glucuronoarabinoxylan (GAX) substitutions can inhibit enzymatic degradation and are involved in the interaction of xylan with cell wall cellulose and lignin, factors which contribute to the recalcitrance of biomass to saccharification. Therefore, identification of xylan characteristics central to biomass biorefining improvement is essential. However, the task of assessing biomass quality is complicated and is often hindered by the lack of a reference for a given crop.

RESULTS

In this study, we created a reference library, expressed in glucose units, of Miscanthus sinensis GAX stem and leaf oligosaccharides, using DNA sequencer-Assisted Saccharide analysis in high throughput (DASH), supported by liquid chromatography (LC), nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS). Our analysis of a number of grass species highlighted variations in substitution type and frequency of stem and leaf GAX. In miscanthus, for example, the β-Xylp-(1 → 2)-α-Araf-(1 → 3) side chain is more abundant in leaf than stem.

CONCLUSIONS

The reference library allows fast identification and comparison of GAX structures from different plants and tissues. Ultimately, this reference library can be used in directing biomass selection and improving biorefining.

Enhancing the Nutritive Value of Corn Whole Stillage for Pigs via Pretreatment and Predigestion

Corn DDGS is poorly digested by pigs. Pretreatment or predigestion of whole stillage (WS; slurry material from which DDGS is derived) can potentially improve corn DDGS digestibility. Thus, a study was conducted to determine the effects of pretreating WS with heat (160 °C and 70 psi for 20 min) alone or in combination with citric acid (10 g/L; CA), sulfuric acid (90 mM; H₂SO₄), or ammonia (1%), without or with subsequent multienzymatic hydrolysis for 24 h, on porcine digestibility. Dried untreated, heat-pretreated, CA-pretreated, H₂SO₄-pretreated, and ammonia-pretreated WS contained 23, 21, 12 19, and 18% total nonstarch polysaccharides, respectively. Pretreatment increased in vitro digestibility of dry matter of WS by ∼11 (CA) to ∼15% units (ammonia). Multienzyme hydrolysis increased in vitro digestibility of dry matter of WS by ∼6 (ammonia-treated WS) to ∼18% units (untreated WS). Thus, pretreatment or predigestion can improve the digestibility of WS and hence the resulting DDGS.

A novel acetyl xylan esterase enabling complete deacetylation of substituted xylans

BACKGROUND

Acetylated 4-O-(methyl)glucuronoxylan (GX) is the main hemicellulose in deciduous hardwood, and comprises a β-(1→4)-linked xylopyranosyl (Xylp) backbone substituted by both acetyl groups and α-(1→2)-linked 4-O-methylglucopyranosyluronic acid (MeGlcpA). Whereas enzymes that target singly acetylated Xylp or doubly 2,3-O-acetyl-Xylp have been well characterized, those targeting (2-O-MeGlcpA)3-O-acetyl-Xylp structures in glucuronoxylan have remained elusive.

RESULTS

An unclassified carbohydrate esterase (FjoAcXE) was identified as a protein of unknown function from a polysaccharide utilization locus (PUL) otherwise comprising carbohydrate-active enzyme families known to target xylan. FjoAcXE was shown to efficiently release acetyl groups from internal (2-O-MeGlcpA)3-O-acetyl-Xylp structures, an activity that has been sought after but lacking in known carbohydrate esterases. FjoAcXE action boosted the activity of α-glucuronidases from families GH67 and GH115 by five and nine times, respectively. Moreover, FjoAcXE activity was not only restricted to GX, but also deacetylated (3-O-Araf)2-O-acetyl-Xylp of feruloylated xylooligomers, confirming the broad substrate range of this new carbohydrate esterase.

CONCLUSION

This study reports the discovery and characterization of the novel carbohydrate esterase, FjoAcXE. In addition to cleaving singly acetylated Xylp, and doubly 2,3-O-acetyl-Xylp, FjoAcXE efficiently cleaves internal 3-O-acetyl-Xylp linkages in (2-O-MeGlcpA)3-O-acetyl-Xylp residues along with densely substituted and branched xylooligomers; activities that until now were missing from the arsenal of enzymes required for xylan conversion.

Characterisation of non-degraded oligosaccharides in enzymatically hydrolysed and fermented, dilute ammonia-pretreated corn stover for ethanol production

BACKGROUND

Corn stover is lignocellulosic biomass that has potential to be used as raw material for bioethanol production. In the current research, dilute ammonia pretreatment was used to improve the accessibility of corn stover carbohydrates to subsequently added hydrolytic enzymes. Some carbohydrates, however, were still present after enzymatic hydrolysis and fermentation. Hence, this research was aimed to characterise the recalcitrant carbohydrates, especially the oligosaccharides that remained after hydrolysis and fermentation of dilute ammonia-pretreated corn stover (DACS).

RESULTS

About 35% (w/w) of DACS carbohydrates remained after enzymatic hydrolysis and fermentation of the released monosaccharides. One-third of these recalcitrant carbohydrates were water soluble and composed of diverse oligosaccharides. By using UHPLC-MS n , more than 50 oligosaccharides were detected. Glucurono-xylooligosaccharides (UAXOS) with a degree of polymerisation (DP) less than 5 were the most abundant oligosaccharides. The (4-O-methyl) glucuronosyl substituent was mostly attached onto the terminal xylosyl residue. It was shown that the glucuronosyl substituent in some UAXOS was modified into a hexenuronosyl, a glucuronamide or a hexenuronamide residue due to the dilute ammonia pretreatment. Another group of abundant oligosaccharides comprised various xyloglucan oligosaccharides (XGOS), with a DP 5 annotated as XXG as the most pronounced. In addition, disaccharides annotated as xylosyl-glucose with different β linkages as well as larger carbohydrates were present in the fermentation slurry.

CONCLUSIONS

Around one-third of the 35% (w/w) recalcitrant DACS carbohydrates remained as water-soluble saccharides. In this study, more than 50 recalcitrant oligosaccharides were detected, which mostly composed of xylosyl and/or glucosyl residues. The most pronounced oligosaccharides were UAXOS and XGOS. Hence, α-glucuronidase and α-xylosidase were suggested to be added to the enzyme mixture to degrade these oligosaccharides further, and hence the fermentation yield is potentially increased.

RP-UHPLC-UV-ESI-MS/MS analysis of LPMO generated C4-oxidized gluco-oligosaccharides after non-reductive labeling with 2-aminobenzamide

Lytic polysaccharide monooxygenases (LPMOs) are able to cleave recalcitrant polysaccharides, such as cellulose, by oxidizing the C1 and/or C4 atoms. The analysis of the resulting products requires a variety of analytical techniques. Up to now, these techniques mainly focused on the identification of non-oxidized and C1-oxidized oligosaccharides. The analysis of C4-oxidized gluco-oligosaccharides is mostly performed by using high pressure anion exchange chromatography (HPAEC). However, the alkaline conditions used during HPAEC analysis lead to tautomerization of C4-oxidized gluco-oligosaccharides, which limits the use of this technique. Here, we describe the use of reverse phase-ultra high performance liquid chromatography (RP-UHPLC) in combination with non-reductive 2-aminobenzamide (2-AB) labeling. Non-reductive 2-AB labeling enabled separation of C4-oxidized gluco-oligosaccharides from their non-oxidized counterparts. Moreover, RP-UHPLC does not require buffered mobile phases, which reduce mass spectrometry (MS) sensitivity. The latter is seen as an advantage over other techniques such as hydrophilic interaction liquid chromatography and porous graphitized carbon coupled to MS. RP-UHPLC coupled to UV detection and mass spectrometry allowed the identification of both labeled non-oxidized and C4-oxidized oligosaccharides. Non-reductive labeling kept the ketone at the C4-position of LPMO oxidized oligosaccharides intact, while selective reducing agents such as sodium triacetoxyborohydride (STAB) reduced this ketone group. Our results show that RP-UHPLC-UV-ESI-MS in combination with non-reductively 2-AB labeling is a suitable technique for the separation and identification of LPMO-generated C4-oxidized gluco-oligosaccharides.

Enzyme supplementation to improve the nutritional value of fibrous feed ingredients in swine diets fed in dry or liquid form

This study evaluated the effect of xylanase supplementation (with or without), feeding method (dry or liquid), and feedstuff (corn distiller's dried grains with solubles [DDGS] or wheat middlings) on apparent total tract digestibility (ATTD) and apparent ileal digestibility (AID) of GE and nutrients, intestinal morphology, ileal and cecal pH, and VFA concentrations. Sixty-four growing pigs (25.87 ± 0.38kg initial BW) were blocked by BW and sex and randomly assigned to 8 dietary treatments. Within each feedstuff, diets were fed either liquid or dry, without or with xylanase (24,000 birch xylan units/kg feed), for 16 d. Diets contained 3.32 and 3.19 Mcal/kg ME for DDGS- and wheat middlings-based diets, respectively. Pigs were fed restricted at 3 times maintenance ME requirements. Liquid diets were prepared by steeping DDGS or wheat middlings with water (1:3, wt/vol) with or without xylanase for 24 h followed by mixing with a basal ingredient mixture and water to achieve a final ratio of 1:2.5 (wt/vol). During steeping of wheat middlings, some fiber degradation occurred. When xylanase was added in dry wheat middlings diets, AID of GE ( < 0.10) and NDF ( < 0.05) increased compared with dry wheat middlings diets without xylanase (64.50 vs. 54.67% and 52.88 vs. 31.69%, respectively), but supplementation of xylanase did not impact AID of GE and NDF when liquid wheat middlings diets were fed. Xylanase in liquid DDGS diets increased ( < 0.05) the AID of NDF compared with liquid DDGS diets without xylanase, but xylanase did not affect AID of NDF in dry DDGS diets. Xylanase in wheat middlings diets improved ( < 0.05) ATTD of GE and N compared with wheat middlings diets without xylanase (80.37 vs. 78.07% and 80.23 vs. 77.94%, respectively). However, there was no effect of xylanase in DDGS diets. Pigs fed DDGS diets had greater concentrations of butyrate in the cecum ( = 0.001) than pigs fed wheat middlings diets (27.6 vs. 20.4 mmol/L). Pigs fed DDGS diets with xylanase had deeper crypts ( < 0.05) in the jejunum than pigs fed DDGS diets without xylanase (98.20 vs. 86.16 μm), but xylanase had no effect in pigs fed wheat middlings diets. Results suggest that liquid feeding and xylanase supplementation had limited potential to enhance nutrient digestibility in pigs fed DDGS-based diets. However, xylanase supplementation in dry wheat middlings-based diets improved the AID of NDF and ATTD of GE and N, but liquid feeding as pretreatment did not further enhance the nutritional value of wheat middlings-based diets.

β-Glucans and Resistant Starch Alter the Fermentation of Recalcitrant Fibers in Growing Pigs

Interactions among dietary ingredients are often assumed non-existent when evaluating the nutritive value and health effects of dietary fiber. Specific fibers can distinctly affect digestive processes; therefore, digestibility and fermentability of the complete diet may depend on fiber types present. This study aimed to evaluate the effects of readily fermentable fibers (β-glucans and resistant starch) on the degradation of feed ingredients containing more persistent, recalcitrant, fibers. Six semi-synthetic diets with recalcitrant fibers from rapeseed meal (pectic polysaccharides, xyloglucans, and cellulose) or corn distillers dried grain with solubles (DDGS; (glucurono)arabinoxylans and cellulose) with or without inclusion of β-glucans (6%) or retrograded tapioca (40%) substituted for corn starch were formulated. Six ileal-cannulated pigs (BW 28±1.4 kg) were assigned to the diets according to a 6×6 Latin square. β-glucan-extract increased apparent total tract digestibility (ATTD) of non-glucosyl polysaccharides (accounting for ~40% of the fiber-fraction) from rapeseed meal (6%-units, P<0.001), but did not affect non-glucosyl polysaccharides from DDGS. Retrograded tapioca reduced ATTD of non-glucosyl polysaccharides from rapeseed meal and DDGS (>10%-units, P<0.001), indicating that the large amount of resistant starch entering the hindgut was preferentially degraded over recalcitrant fibers from rapeseed meal and DDGS, possibly related to reduced hindgut-retention time following the increased intestinal bulk. Fermentation of fiber sources was not only dependent on fiber characteristics, but also on the presence of other fibers in the diet. Hence, interactions in the gastrointestinal tract among fibrous feed ingredients should be considered when evaluating their nutritive value.

Towards enzymatic breakdown of complex plant xylan structures: State of the art

Significant progress over the past few years has been achieved in the enzymology of microbial degradation and saccharification of plant xylan, after cellulose being the most abundant natural renewable polysaccharide. Several new types of xylan depolymerizing and debranching enzymes have been described in microorganisms. Despite the increasing variety of known glycoside hydrolases and carbohydrate esterases, some xylan structures still appear quite recalcitrant. This review focuses on the mode of action of different types of depolymerizing endoxylanases and their cooperation with β-xylosidase and accessory enzymes in breakdown of complex highly branched xylan structures. Emphasis is placed on the enzymatic hydrolysis of alkali-extracted deesterified polysaccharide as well as acetylated xylan isolated from plant cell walls under non-alkaline conditions. It is also shown how the combination of selected endoxylanases and debranching enzymes can determine the nature of prebiotic xylooligosaccharides or lead to complete hydrolysis of the polysaccharide. The article also highlights the possibility for discovery of novel xylanolytic enzymes, construction of multifunctional chimeric enzymes and xylanosomes in parallel with increasing knowledge on the fine structure of the polysaccharide.

Isolation and characterization of acetylated glucuronoarabinoxylan from sugarcane bagasse and straw

Sugarcane bagasse and straw are generated in large volumes as by-products of agro-industrial production. They are an emerging valuable resource for the generation of hemicellulose-based materials and products, since they contain significant quantities of xylans (often twice as much as in hardwoods). Heteroxylans (yields of ca 20% based on xylose content in sugarcane bagasse and straw) were successfully isolated and purified using mild delignification followed by dimethyl sulfoxide (DMSO) extraction. Delignification with peracetic acid (PAA) was more efficient than traditional sodium chlorite (NaClO₂) delignification for xylan extraction from both biomasses, resulting in higher extraction yields and purity. We have shown that the heteroxylans isolated from sugarcane bagasse and straw are acetylated glucuronoarabinoxylans (GAX), with distinct molecular structures. Bagasse GAX had a slightly lower glycosyl substitution molar ratio of Araf to Xylp to (0.5:10) and (4-O-Me)GlpA to Xylp (0.1:10) than GAX from straw (0.8:10 and 0.1:10 respectively), but a higher degree of acetylation (0.33 and 0.10, respectively). A higher frequency of acetyl groups substitution at position α-(1→3) (Xyl-3Ac) than at position α-(1→2) (Xyl-2Ac) was confirmed for both bagasse and straw GAX, with a minor ratio of diacetylation (Xyl-2,3Ac). The size and molecular weight distributions for the acetylated GAX extracted from the sugarcane bagasse and straw were analyzed using multiple-detection size-exclusion chromatography (SEC-DRI-MALLS). Light scattering data provided absolute molar mass values for acetylated GAX with higher average values than did standard calibration. Moreover, the data highlighted differences in the molar mass distributions between the two isolation methods for both types of sugarcane GAX, which can be correlated with the different Araf and acetyl substitution patterns. We have developed an empirical model for the molecular structure of acetylated GAX extracted from sugarcane bagasse and straw with PAA/DMSO through the integration of results obtained from glycosidic linkage analysis, ¹H NMR spectroscopy and acetyl quantification. This knowledge of the structure of xylans in sugarcane bagasse and straw will provide a better understanding of the isolation-structure-properties relationship of these biopolymers and, ultimately, create new possibilities for the use of sugarcane xylan in high-value applications, such as biochemicals and bio-based materials.

The two Rasamsonia emersonii α-glucuronidases, ReGH67 and ReGH115, show a different mode-of-action towards glucuronoxylan and glucuronoxylo-oligosaccharides

BACKGROUND

The production of biofuels and biochemicals from grass-type plant biomass requires a complete utilisation of the plant cellulose and hemicellulosic xylan via enzymatic degradation to their constituent monosaccharides. Generally, physical and/or thermochemical pretreatments are performed to enable access for the subsequent added carbohydrate-degrading enzymes. Nevertheless, partly substituted xylan structures remain after pretreatment, in particular the ones substituted with (4-O-methyl-)glucuronic acids (UAme). Hence, α-glucuronidases play an important role in the degradation of UAmexylan structures facilitating the complete utilisation of plant biomass. The characterisation of α-glucuronidases is a necessity to find the right enzymes to improve degradation of recalcitrant UAmexylan structures.

RESULTS

The mode-of-action of two α-glucuronidases was demonstrated, both obtained from the fungus Rasamsonia emersonii; one belonging to the glycoside hydrolase (GH) family 67 (ReGH67) and the other to GH115 (ReGH115). Both enzymes functioned optimal at around pH 4 and 70 °C. ReGH67 was able to release UAme from UAme-substituted xylo-oligosaccharides (UAmeXOS), but only the UAme linked to the non-reducing end xylosyl residue was cleaved. In particular, in a mixture of oligosaccharides, UAmeXOS having a degree of polymerisation (DP) of two were hydrolysed to a further extent than longer UAmeXOS (DP 3-4). On the contrary, ReGH115 was able to release UAme from both polymeric UAmexylan and UAmeXOS. ReGH115 cleaved UAme from both internal and non-reducing end xylosyl residues, with the exception of UAme attached to the non-reducing end of a xylotriose oligosaccharide.

CONCLUSION

In this research, and for the first time, we define the mode-of-action of two α-glucuronidases from two different GH families both from the ascomycete R. emersonii. To date, only four α-glucuronidases classified in GH115 are characterised. ReGH67 showed limited substrate specificity towards only UAmeXOS, cleaving UAme only when attached to the non-reducing end xylosyl residue. ReGH115 was much less substrate specific compared to ReGH67, because UAme was released from both polymeric UAmexylan and UAmeXOS, from both internal and non-reducing end xylosyl residues. The characterisation of the mode-of-action of these two α-glucuronidases helps understand how R. emersonii attacks UAmexylan in plant biomass and the knowledge presented is valuable to improve enzyme cocktails for biorefinery applications.

Potential of Using Maize Cobs in Pig Diets - A Review

The quest to broaden the narrow range of feed ingredients available to pig producers has prompted research on the use of low cost, unconventional feedstuffs, which are typically fibrous and abundant. Maize cobs, a by-product of a major cereal grown worldwide, have potential to be used as a pig feed ingredient. Presently, maize cobs are either dumped or burnt for fuel. The major challenge in using maize cobs in pig diets is their lignocellulosic nature (45% to 55% cellulose, 25% to 35% hemicellulose, and 20% to 30% lignin) which is resistant to pigs' digestive enzymes. The high fiber in maize cobs (930 g neutral detergent fiber/kg dry matter [DM]; 573 g acid detergent fiber/kg DM) increases rate of passage and sequestration of nutrients in the fiber reducing their digestion. However, grinding, heating and fermentation can modify the structure of the fibrous components in the maize cobs and improve their utilization. Pigs can also extract up to 25% of energy maintenance requirements from fermentation products. In addition, dietary fiber improves pig intestinal health by promoting the growth of lactic acid bacteria, which suppress proliferation of pathogenic bacteria in the intestines. This paper reviews maize cob composition and the effect on digestibility of nutrients, intestinal microflora and growth performance and proposes the use of ensiling using exogenous enzymes to enhance utilization in diets of pigs.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2009-2010

This review is the sixth update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2010. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, arrays and fragmentation are covered in the first part of the review and applications to various structural typed constitutes the remainder. The main groups of compound that are discussed in this section are oligo and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Many of these applications are presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis.

Analysis of by-product formation and sugar monomerization in sugarcane bagasse pretreated at pilot plant scale: differences between autohydrolysis, alkaline and acid pretreatment

Sugarcane bagasse is an interesting feedstock for the biobased economy since a large fraction is polymerized sugars. Autohydrolysis, alkaline and acid pretreatment conditions combined with enzyme hydrolysis were used on lignocellulose rich bagasse to acquire monomeric. By-products found after pretreatment included acetic, glycolic and coumaric acid in concentrations up to 40, 21 and 2.5 g/kg dry weight bagasse respectively. Alkaline pretreated material contained up to 45 g/kg bagasse DW of sodium. Acid and autohydrolysis pretreatment results in a furan formation of 14 g/kg and 25 g/kg DW bagasse respectively. Enzyme monomerization efficiencies of pretreated solid material after 72 h were 81% for acid pretreatment, 77% for autohydrolysis and 57% for alkaline pretreatment. Solid material was washed with superheated water to decrease the amount of by-products. Washing decreased organic acid, phenol and furan concentrations in solid material by at least 60%, without a major sugar loss.

Isolation and characterization of feruloylated arabinoxylan oligosaccharides from the perennial cereal grain intermediate wheat grass (Thinopyrum intermedium)

In comparison to the annual grain crops dominating current agricultural production, perennial grain species require fewer chemical and energy inputs and improve soil health and erosion control. The possibility for producing sustainable grain harvests from marginal land areas is motivating research initiatives to integrate perennial grains into commercial cropping and food processing systems. In this study, the feruloylated arabinoxylans from intermediate wheat grass (Thinopyrum intermedium, IWG), a promising perennial grain candidate in agronomic screening studies, were investigated. Insoluble fiber isolated from IWG whole grain flour was subjected to either mildly acidic (50 mM TFA, 100 °C, 2 h) or enzymatic (Driselase) hydrolysis. The liberated feruloylated arabinoxylan oligosaccharides were concentrated with Amberlite XAD-2, separated with gel chromatography (Sephadex LH-20, water), and purified with reversed-phase HPLC (C18, water-MeOH gradient). Thirteen feruloylated oligosaccharides were isolated (including eight structures described for the first time) and identified by LC-ESI-MS and NMR. Linkage-type analysis via methylation analysis, as well as the monosaccharide and phenolic acid profiles of the IWG insoluble fiber were also determined. IWG feruloylated arabinoxylans have a relatively simple structure with only short feruloylated side chains, a lower backbone substitution rate than annual rye and wheat varieties, and a moderate phenolic acid content.

Quantitative Profiling of Feruloylated Arabinoxylan Side-Chains from Graminaceous Cell Walls

Graminaceous arabinoxylans are distinguished by decoration with feruloylated monosaccharidic and oligosaccharidic side-chains. Although it is hypothesized that structural complexity and abundance of these feruloylated arabinoxylan side-chains may contribute, among other factors, to resistance of plant cell walls to enzymatic degradation, quantitative profiling approaches for these structural units in plant cell wall materials have not been described yet. Here we report the development and application of a rapid and robust method enabling the quantitative comparison of feruloylated side-chain profiles in cell wall materials following mildly acidic hydrolysis, C18-solid phase extraction (SPE), reduction under aprotic conditions, and liquid chromatography with diode-array detection/mass spectrometry (LC-DAD/MS) separation and detection. The method was applied to the insoluble fiber/cell wall materials isolated from 12 whole grains: wild rice (Zizania aquatica L.), long-grain brown rice (Oryza sativa L.), rye (Secale cereale L.), kamut (Triticum turanicum Jakubz.), wheat (Triticum aestivum L.), spelt (Triticum spelta L.), intermediate wheatgrass (Thinopyrum intermedium), maize (Zea mays L.), popcorn (Zea mays L. var. everta), oat (Avena sativa L.) (dehulled), barley (Hordeum vulgare L.) (dehulled), and proso millet (Panicum miliaceum L.). Between 51 and 96% of the total esterified monomeric ferulates were represented in the quantified compounds captured in the feruloylated side-chain profiles, which confirms the significance of these structures to the global arabinoxylan structure in terms of quantity. The method provided new structural insights into cereal grain arabinoxylans, in particular, that the structural moiety α-l-galactopyranosyl-(1→2)-β-d-xylopyranosyl-(1→2)-5-O-trans-feruloyl-l-arabinofuranose (FAXG), which had previously only been described in maize, is ubiquitous to cereal grains.

Conversion of sugar beet leaf polysaccharides into single cell protein

Conversion of low-cost sugar beet leaves into valuable yeast biomass was described.

Lignin triggers irreversible cellulase loss during pretreated lignocellulosic biomass saccharification

BACKGROUND

Non-productive binding of enzymes to lignin is thought to impede the saccharification efficiency of pretreated lignocellulosic biomass to fermentable sugars. Due to a lack of suitable analytical techniques that track binding of individual enzymes within complex protein mixtures and the difficulty in distinguishing the contribution of productive (binding to specific glycans) versus non-productive (binding to lignin) binding of cellulases to lignocellulose, there is currently a poor understanding of individual enzyme adsorption to lignin during the time course of pretreated biomass saccharification.

RESULTS

In this study, we have utilized an FPLC (fast protein liquid chromatography)-based methodology to quantify free Trichoderma reesei cellulases (namely CBH I, CBH II, and EG I) concentration within a complex hydrolyzate mixture during the varying time course of biomass saccharification. Three pretreated corn stover (CS) samples were included in this study: Ammonia Fiber Expansion(a) (AFEX™-CS), dilute acid (DA-CS), and ionic liquid (IL-CS) pretreatments. The relative fraction of bound individual cellulases varied depending not only on the pretreated biomass type (and lignin abundance) but also on the type of cellulase. Acid pretreated biomass had the highest levels of non-recoverable cellulases, while ionic liquid pretreated biomass had the highest overall cellulase recovery. CBH II has the lowest thermal stability among the three T. reesei cellulases tested. By preparing recombinant family 1 carbohydrate binding module (CBM) fusion proteins, we have shown that family 1 CBMs are highly implicated in the non-productive binding of full-length T. reesei cellulases to lignin.

CONCLUSIONS

Our findings aid in further understanding the complex mechanisms of non-productive binding of cellulases to pretreated lignocellulosic biomass. Developing optimized pretreatment processes with reduced or modified lignin content to minimize non-productive enzyme binding or engineering pretreatment-specific, low-lignin binding cellulases will improve enzyme specific activity, facilitate enzyme recycling, and thereby permit production of cheaper biofuels.