Variation in the chemical composition of wheat straw: the role of tissue ratio and composition

Sustainable Alternatives to the Reduction of Plastic Straws Used with Chilled Equine Semen

Currently, plastic is used being without any limitations. The livestock sector is no stranger to its use. For example, artificial insemination involves the use of different plastic materials, including semen straws and insemination catheters, which increase the levels of waste in our environment. Finding a sustainable solution to avoid plastic materials is a challenge. The aim of this study was to examine different biodegradable materials as alternatives to conventional syringes used for refrigerated equine semen. The materials tested were bamboo, avocado, grass, paper, Kraft paper, wheat, and rice. Bamboo and avocado were selected to continue testing with the refrigerated semen with a lifespan extended by INRA 96®; the rest of the materials did not meet the requirements necessary for preservation. Motility and movement kinetics tests were performed at 24 and 96 h of refrigeration to evaluate semen quality; relative to the control, significantly better results were displayed in regard to the total and progressive motility avocado straws. The kinetic parameters were comparable to the control for both materials and within normal ranges. After performing a microbiological control process for both straws, it was confirmed that there was no bacterial growth in either straw. We can confirm that avocado straws can be used to preserve chilled equine semen, guaranteeing seminal quality while being respectful to the environment.

Biocalorimetry-aided monitoring of fungal pretreatment of lignocellulosic agricultural residues

The present study aimed to investigate whether and how non-invasive biocalorimetric measurements could serve for process monitoring of fungal pretreatment during solid-state fermentation (SSF) of lignocellulosic agricultural residues such as wheat straw. Seven filamentous fungi representing different lignocellulose decay types were employed. Water-soluble sugars being immediately available after fungal pretreatment and those becoming water-extractable after enzymatic digestion of pretreated wheat straw with hydrolysing (hemi)cellulases were considered to constitute the total bioaccessible sugar fraction. The latter was used to indicate the success of pretreatments and linked to corresponding species-specific metabolic heat yield coefficients (YQ/X) derived from metabolic heat flux measurements during fungal wheat straw colonisation. An YQ/X range of about 120 to 140 kJ/g was seemingly optimal for pretreatment upon consideration of all investigated fungi and application of a non-linear Gaussian fitting model. Upon exclusion from analysis of the brown-rot basidiomycete Gloeophyllum trabeum, which differs from all other here investigated fungi in employing extracellular Fenton chemistry for lignocellulose decomposition, a linear relationship where amounts of total bioaccessible sugars were suggested to increase with increasing YQ/X values was obtained. It remains to be elucidated whether an YQ/X range being optimal for fungal pretreatment could firmly be established, or if the sugar accessibility for post-treatment generally increases with increasing YQ/X values as long as "conventional" enzymatic, i.e. (hemi)cellulase-based, lignocellulose decomposition mechanisms are operative. In any case, metabolic heat measurement-derived parameters such as YQ/X values may become very valuable tools supporting the assessment of the suitability of different fungal species for pretreatment of lignocellulosic substrates. KEY POINTS: • Biocalorimetry was used to monitor wheat straw pretreatment with seven filamentous fungi. • Metabolic heat yield coefficients (YQ/X) seem to indicate pretreatment success. • YQ/X values may support the selection of suitable fungal strains for pretreatment.

Preparation of Wheat Straw Hot-Pressed Board through Coupled Dilute Acid Pretreatment and Surface Modification

The production of wheat straw waste board materials encounters challenges, including inadequate inherent adhesiveness and the utilization of environmentally harmful adhesives. Employing a hot-pressed method for converting wheat straw into board materials represents a positive stride towards the resourceful utilization of agricultural wastes. This study primarily focuses on examining the influence of hot-pressing process conditions on the mechanical properties of wheat straw board materials pretreated with dilute acid. Additionally, it assesses the necessity of dilute acid treatment and optimizes the hot-pressing conditions to achieve optimal results at 15 MPa, 2 h, and 160 °C. Furthermore, a comprehensive process is developed for preparing wheat straw hot-pressed board materials by combining dilute acid pretreatment with surface modification treatments, such as glutaraldehyde, citric acid, and rosin. Finally, a thorough characterization of the mechanical properties of the prepared board materials is conducted. The results indicate a substantial improvement in tensile strength across all modified wheat straw board materials compared to untreated ones. Notably, boards treated with glutaraldehyde exhibited the most significant enhancement, achieving a tensile strength of 463 kPa, bending strength of 833 kPa, and a water absorption rate of 14.14%. This study demonstrates that combining dilute acid pretreatment with surface modification treatments effectively enhances the performance of wheat straw board materials, offering a sustainable alternative to traditional wood-based board materials.

Enhancing crop yields through improvements in the efficiency of photosynthesis and respiration

The rate with which crop yields per hectare increase each year is plateauing at the same time that human population growth and other factors increase food demand. Increasing yield potential (Y p ) of crops is vital to address these challenges. In this review, we explore a component ofY p that has yet to be optimised - that being improvements in the efficiency with which light energy is converted into biomass (ε c ) via modifications to CO2 fixed per unit quantum of light (α), efficiency of respiratory ATP production (ε prod ) and efficiency of ATP use (ε use ). For α, targets include changes in photoprotective machinery, ribulose bisphosphate carboxylase/oxygenase kinetics and photorespiratory pathways. There is also potential forε prod to be increased via targeted changes to the expression of the alternative oxidase and mitochondrial uncoupling pathways. Similarly, there are possibilities to improveε use via changes to the ATP costs of phloem loading, nutrient uptake, futile cycles and/or protein/membrane turnover. Recently developed high-throughput measurements of respiration can serve as a proxy for the cumulative energy cost of these processes. There are thus exciting opportunities to use our growing knowledge of factors influencing the efficiency of photosynthesis and respiration to create a step-change in yield potential of globally important crops.

Biomass Pre-Extraction as a Versatile Strategy to Improve Biorefinery Feedstock Flexibility, Sugar Yields, and Lignin Purity

Feedstock flexibility is highly advantageous for the viability of (solvent-based) biorefineries but comes with the considerable challenge of having to cope with the varying nature and typically high abundance of nonlignocellulose compounds in the most readily available residual biomass streams. Here, we demonstrate that mild aqueous acetone organosolv fractionation of various complex lignocellulosic raw materials (roadside grass, wheat straw, birch branches, almond shells, and a mixed stream thereof) is indeed negatively affected by these compounds and present a versatile strategy to mitigate this bottleneck in biorefining. A biomass pre-extraction approach has been developed to remove the detrimental extractives with (aqueous) acetone prior to fractionation. Pre-extraction removed organic extractives as well as minerals, primarily reducing acid dose requirements for fractionation and loss of hemicellulose sugars by degradation and improved the purity of the isolated lignin. We show how pre-extraction affects the effectiveness of the biorefinery process, including detailed mass balances for pretreatment, downstream processing, and product characteristics, and how it affects solvent and energy use with a first conceptual process design. The integrated biorefining approach allows for the improved compatibility of biorefineries with sustainable feedstock supply chains, enhanced biomass valorization (i.e., isolation of bioactive compounds from the extract), and more effective biomass processing with limited variation in product quality.

Applicability and information value of biocalorimetry for the monitoring of fungal solid-state fermentation of lignocellulosic agricultural by-products

The applicability of biocalorimetry for monitoring fungal conversion of lignocellulosic agricultural by-products during solid-state fermentation (SSF) was substantiated through linking the non-invasive measurement of metabolic heat fluxes to conventional invasive determination of fungal activity (growth, substrate degradation, enzyme activity) parameters. For this, the fast-growing, cellulose-utilising ascomycete Stachybotrys chlorohalonata and the comparatively slow-growing litter-decay basidiomycete Stropharia rugosoannulata were investigated as model organisms during growth on solid wheat straw. Both biocalorimetric and non-calorimetric data may suggest R (ruderal)- and C (combative)-selected life history strategies in S. chlorohalonata and S. rugosoannulata, respectively. For both species, a strong linear correlation of the released metabolic heat with the corresponding fungal biomass was observed. Species-specific Y_Q/X values (metabolic heat released per fungal biomass unit) were obtained, which potentially enable use of biocalorimetric signals for the quantification of fungal biomass during single-species SSF processes. Moreover, Y_Q/X values may also indicate different fungal life history strategies and therefore be considered as useful parameters aiding fungal ecology research.

Inventory review and environmental evaluation of first- and second-generation sugars through life cycle assessment

In recent years, there has been a great movement towards the generation of knowledge related to the biorefinery concept. First-generation biorefineries bear the stigma of using arable land and edible crops for fuel instead of as sources of food and feed. However, second-generation biorefineries have not reached the level of full technical feasibility. Bearing in mind the objective of sugar production from sugar, starch, or lignocellulosic raw materials, the purpose of this study is to assess the environmental impact of first- and second-generation biorefineries, considering as an example for the comparative evaluation, the production of sugar fractions from crops (starch and sugar crops), and lignocellulosic biomass (hardwood and softwood). The characterization results were obtained using the ReCiPe 1.1 model, implemented through the SimaPro 9.0 software. Both production systems are inherently different and have strengths and weaknesses that must be carefully analyzed. The resulting environmental profile shows that the silviculture of wood contributes less to the environmental impact than cropping activities in most impact categories. In general, this study suggests that first-generation systems are burdened environmentally by the use of fertilizers, which have a significant impact on categories such as marine and freshwater eutrophication and terrestrial acidification, while second-generation systems are limited by the intensive processing steps needed for delignification, typically involving the use of chemicals and/or energy. LCA in early stages of the production of bio-based building blocks, rather than on the manufacture of biofuels or bioplastics, allows the precise identification of the environmental burdens that may be influencing the overall environmental profile of a biorefinery.

Heat Stress Impact on Yield and Composition of Quinoa Straw under Mediterranean Field Conditions

Quinoa (Chenopodium quinoa Willd.) is receiving increasing attention globally due to the high nutritional value of its seeds, and the ability of this crop to cope with stress. In the current climate change scenario, valorization of crop byproducts is required to support a climate-smart agriculture. Furthermore, research works characterizing and evaluating quinoa stems and their putative uses are scarce. In this work, straw yield and composition, and the relative feed value of five quinoa varieties, were analyzed in two consecutive years (2017-2018) under field conditions in Southwestern Europe. High temperatures were recorded during the 2017 growing season resulting in significantly decreased straw yield and improved feed value, associated with compositional changes under elevated temperatures. Crude protein, ash, phosphorus, and calcium contents were higher under high temperatures, whereas fiber contents decreased. The relative feed value was also higher in 2017 and differed among varieties. Differences among varieties were also found in straw yield, and contents of phosphorus, potassium, and calcium. Overall, the results presented here support a sustainable quinoa productive system by encouraging straw valorization and shedding light on the mechanisms underlying heat-stress responses in this crop.

Cross-feeding and wheat straw extractives enhance growth of Clostridium thermocellum-containing co-cultures for consolidated bioprocessing

Co-cultures consisting of three thermophilic and lignocellulolytic bacteria, namely Clostridium thermocellum, C. stercorarium, and Thermoanaerobacter thermohydrosulfuricus, degrade lignocellulosic material in a synergistic manner. When cultured in a defined minimal medium two of the members appeared to be auxotrophic and unable to grow, but the growth of all species was observed in all co-culture combinations, indicating cross-feeding of unidentified growth factors between the members. Growth factors also appeared to be present in water-soluble extractives obtained from wheat straw, allowing for the growth of the auxotrophic monocultures in the defined minimal medium. Cell enumeration during growth on wheat straw in this medium revealed different growth profiles of the members that varied between the co-cultures. End-product profiles also varied substantially between the cultures, with significantly higher ethanol production in all co-cultures compared to the mono-cultures. Understanding interactions between co-culture members, and the additional nutrients provided by lignocellulosic substrates, will aid us in consolidated bioprocessing design.

Variation in Lignin, Cell Wall-Bound p-Coumaric, and Ferulic Acid in the Nodes and Internodes of Cereals and Their Impact on Lodging

Understanding the contribution of stem cell wall components to lodging is important in developing breeding programs aimed at reducing lodging in cereal crops. This study is one of the first to investigate the correlation between the amounts of cell wall-bound ferulic acid, p-coumaric acid, and lignin in the nodes and internodes of cereals (oat, wheat, and barley) and their lodging susceptibility during grain fill. All samples, except two-row barley, were susceptible to lodging and expressed a significantly lower stalk strength. Lignin and phenolic contents between nodes and internodes of all samples were significantly different, with internodes having higher amounts (5.5-7.0 and 10.9-16.2 μg/g p-coumaric acid, and 2.5-3.2 and 3.9-7.1 μg/g ferulic acid in nodes and internodes, respectively). The acid-soluble lignin content was different between nodes and internodes but not between crops. This data set did not correlate with lodging classification, possibly due to sample size and type.

Pressurised disc refining of wheat straw as a pre-treatment approach for agricultural residues: A preliminary assessment of energy consumption and fibre composition

This preliminary study assesses a potential pre-treatment approach for agricultural residues, in order to improve enzyme access and cellulose digestibility that increased with increasing refining pressure. Wheat straw, an important European agri-residue, was chopped then refined at pilot-scale under different pressures (4-10 bar) and two refiner plate configurations. The most energy efficient runs used 0.94-0.96 kWh electricity; 8.9-11.0 MJ heat per kg dry matter fibre. A scaling factor specific to the machinery used in the trial suggested that wheat straw could be refined using approximately 160 kWh electricity and 980-1900 MJ heat per tonne DM yield at commercial-scale. Hemicellulose content in wheat straw at 31.8% decreased to the lowest level of 14.6% after refining at 10 bar. Pressurised disc refining did not appear to produce significant quantities of acetic acid, a key fermentation inhibitor, that could limit microbial fermentation.

Impact of the Type of Fertilization and the Addition of Glycerol on the Quality of Spring Rape Straw Pellets

This paper presents an analysis of selected qualitative characteristics of pellets produced from rape straw obtained from cultivations subjected to different fertilization treatments and from mixtures of straw selected for testing with crude glycerol obtained as a by-product from biodiesel production. The assessment focused on the following qualities of the obtained pellets: Moisture content, mechanical durability, heating value and main elements, that is, carbon, hydrogen, nitrogen, sulphur, chlorine and oxygen. The obtained results indicated that the different treatment regimens applied in spring rape cultivations had a significant impact on the physicochemical qualities of the straw. In terms of the heating value, traditional fertilization with multi-component fertilizer (NPK) yielded slightly lower chemical parameters (lower carbon content and heat of combustion) than in the case of straw obtained from the control sample and from the plot fertilized with digestate. Furthermore, in all of the analysed mixtures, the 10% addition of raw glycerol improved the mechanical characteristics of the produced straw pellets. After the 10% glycerol addition, in terms of the energetic use of these biofuels, the parameters of the fuel, such as heating value and net heating value, were slightly decreased.

Effect of straw amount on feed intake and weight gain in growing pigs housed in pens with partly slatted floor

The provision of straw to pigs kept in conventional pens with concrete floor improves animal welfare, but the effects of straw on pigs' performance are unclear. In two steps, we investigated the relationship between amount of straw provided to pigs and measures of performance in a set-up maintaining constant space allowance and controlled room temperature. From approximately 30- to 85-kg BW, pigs were housed in groups of 18 in pens (5.48 m × 2.48 m) with concrete floor (1/3 solid, 1/3 drained and 1/3 slatted). The pens were cleaned manually twice a week, and the designated amount of fresh uncut wheat straw was provided daily onto the solid part of the floor. In the first step, 48 pens were assigned to 10-, 500- or 1000-g straw per pig per day, while in the second step, 90 pens were assigned to 10-, 80-, 150-, 220-, 290-, 360-, 430- or 500-g straw per pig per day. Pigs were weighed at the start of the experimental period at approximately 30 kg and again at approximately 85-kg BW. The average daily gain increased 8.1 g (SEM 17) for every extra 100-g straw added daily (P < 0.001) resulting in 40 g higher average daily gain with 500 compared to 10-g straw per pig per day. The feed conversion ratio was not affected by the amount of straw provided, as the feed intake tended to be higher with increasing amounts of straw. Thus, between 10 and 500 g, the more straw provided, the higher the daily weight gain. As the nutritional value of straw is considered minimal, this result is likely due to improved gut health from the increasing amounts of straw ingested and increased feed intake due to increased stimulation of exploratory behaviour with increasing amounts of straw available, or a combination of these. The observed tendency for a higher feed intake supports this suggestion, but studies are needed to establish the impact of these two contributing factors.

Biofuel production from straw hydrolysates: current achievements and perspectives

Straw is an agricultural residue of the production of e.g. cereals, rapeseed or sunflowers. It includes dried stalks, leaves, and empty ears and corncobs, which are separated from the grains during harvest. Straw is a promising lignocellulosic feedstock with a beneficial greenhouse gas balance for the production of biofuels and chemicals. Like all lignocellulosic materials, straw is recalcitrant and requires thermochemical and enzymatic pretreatment to enable access to the three major biopolymers of straw-the polysaccharides cellulose and hemicellulose and the polyaromatic compound lignin. Straw is used for commercial ethanol and biogas production. Considerable research has also been conducted to produce biobutanol, biodiesel and biochemicals from this raw material, but more research is required to establish them on a commercial scale. The major hindrance for launching industrial biofuel and chemicals' production from straw is the high cost necessitated by pretreatment of the material. Improvements of microbial strains, production and extraction technologies, as well as co-production of high-value compounds represent ways of establishing straw as feedstock for the production of biofuels, chemicals and food.

Integrative visual omics of the white-rot fungus Polyporus brumalis exposes the biotechnological potential of its oxidative enzymes for delignifying raw plant biomass

BACKGROUND

Plant biomass conversion for green chemistry and bio-energy is a current challenge for a modern sustainable bioeconomy. The complex polyaromatic lignin polymers in raw biomass feedstocks (i.e., agriculture and forestry by-products) are major obstacles for biomass conversions. White-rot fungi are wood decayers able to degrade all polymers from lignocellulosic biomass including cellulose, hemicelluloses, and lignin. The white-rot fungus Polyporus brumalis efficiently breaks down lignin and is regarded as having a high potential for the initial treatment of plant biomass in its conversion to bio-energy. Here, we describe the extraordinary ability of P. brumalis for lignin degradation using its enzymatic arsenal to break down wheat straw, a lignocellulosic substrate that is considered as a biomass feedstock worldwide.

RESULTS

We performed integrative multi-omics analyses by combining data from the fungal genome, transcriptomes, and secretomes. We found that the fungus possessed an unexpectedly large set of genes coding for Class II peroxidases involved in lignin degradation (19 genes) and GMC oxidoreductases/dehydrogenases involved in generating the hydrogen peroxide required for lignin peroxidase activity and promoting redox cycling of the fungal enzymes involved in oxidative cleavage of lignocellulose polymers (36 genes). The examination of interrelated multi-omics patterns revealed that eleven Class II Peroxidases were secreted by the fungus during fermentation and eight of them where tightly co-regulated with redox cycling enzymatic partners.

CONCLUSION

As a peculiar feature of P. brumalis, we observed gene family extension, up-regulation and secretion of an abundant set of versatile peroxidases and manganese peroxidases, compared with other Polyporales species. The orchestrated secretion of an abundant set of these delignifying enzymes and redox cycling enzymatic partners could contribute to the delignification capabilities of the fungus. Our findings highlight the diversity of wood decay mechanisms present in Polyporales and the potentiality of further exploring this taxonomic order for enzymatic functions of biotechnological interest.

Genotypic effects on sugar and by-products of liquid hydrolysates and on saccharification of acid-insoluble residues from wheat straw

Wheat straw is one of the major attractive resources for low-cost raw materials for renewable energy, biofuels and biochemicals. However, like other sources of lignocellulosic biomass, straw is a heterogeneous material due to its mixed origin from different tissue and cell types. Here, to examine the genotypic effects on biorefinery usage of wheat straw, straw obtained from different wheat cultivars and experimental lines was pretreated with dilute acid. Significant differences between cultivars were observed in the concentrations of glucose and toxic by-products of the liquid hydrolysates. A higher content of xylose than glucose was found in liquid hydrolysates from wheat straw, and the xylose content appeared to be affected by both environmental and genetic factors. Analysis using chromosome substitution lines of the common wheat cultivar Chinese Spring showed that chromosomes 2A and 3A from other wheat cultivars, Hope and Timstein, significantly increased the xylose content. However, no significant relationship was observed between the liquid hydrolysate xylose content and the glucose content obtained from enzymatic saccharification of the acid-insoluble residue. These results highlight the potential of wheat breeding to improve biomass-related traits in wheat straw.

Release of cell wall phenolic esters during hydrothermal pretreatment of rice husk and rice straw

BACKGROUND

Rice husk and rice straw represent promising sources of biomass for production of renewable fuels and chemicals. For efficient utilisation, lignocellulosic components must first be pretreated to enable efficient enzymatic saccharification and subsequent fermentation. Existing pretreatments create breakdown products such as sugar-derived furans, and lignin-derived phenolics that inhibit enzymes and fermenting organisms. Alkali pretreatments have also been shown to release significant levels of simple, free phenolics such as ferulic acid that are normally esterified to cell wall polysaccharides in the intact plant. These phenolics have recently been found to have considerable inhibitory properties. The aim of this research has been to establish the extent to which such free phenolic acids are also released during hydrothermal pretreatment of rice straw (RS) and rice husk (RH).

RESULTS

RS and RH were subjected to hydrothermal pretreatments over a wide range of severities (1.57-5.45). FTIR analysis showed that the pretreatments hydrolysed and solubilised hemicellulosic moieties, leading to an enrichment of lignin and crystalline cellulose in the insoluble residue. The residues also lost the capacity for UV autofluorescence at pH 7 or pH 10, indicating the breakdown or release of cell wall phenolics. Saponification of raw RS and RH enabled identification and quantification of substantial levels of simple phenolics including ferulic acid (tFA), coumaric acid (pCA) and several diferulic acids (DiFAs) including 8-O-4'-DiFA, 8,5'-DiFA and 5,5'-DiFA. RH had higher levels of pCA and lower levels of tFA and DiFAs compared with RS. Assessment of the pretreatment liquors revealed that pretreatment-liberated phenolics present were not free but remained as phenolic esters (at mM concentrations) that could be readily freed by saponification. Many were lost, presumably through degradation, at the higher severities.

CONCLUSION

Differences in lignin, tFA, DiFAs and pCA between RS and RH reflect differences in cell wall physiology, and probably contribute to the higher recalcitrance of RH compared with RS. Hydrothermal pretreatments, unlike alkali pretreatments, release cinnamic acid components as esters. The potential for pretreatment-liberated phenolic esters to be inhibitory to fermenting microorganisms is not known. However, the present study shows that they are found at concentrations that could be significantly inhibitory if released as free forms by enzyme activity.

Potential of a gypsum-free composting process of wheat straw for mushroom production

Wheat straw based composting generates a selective substrate for mushroom production. The first phase of this process requires 5 days, and a reduction in time is wished. Here, we aim at understanding the effect of gypsum on the duration of the first phase and the mechanism behind it. Hereto, the regular process with gypsum addition and the same process without gypsum were studied during a 5-day period. The compost quality was evaluated based on compost lignin composition analysed by py-GC/MS and its degradability by a commercial (hemi-)cellulolytic enzyme cocktail. The composting phase lead to the decrease of the pyrolysis products 4-vinylphenol and 4-vinylguaiacol that can be associated with p-coumarates and ferulates linking xylan and lignin. In the regular compost, the enzymatic conversion reached 32 and 39% for cellulose, and 23 and 32% for xylan after 3 and 5 days, respectively. In absence of gypsum similar values were reached after 2 and 4 days, respectively. Thus, our data show that in absence of gypsum the desired compost quality was reached 20% earlier compared to the control process.

Variation across a wheat genetic diversity panel for saccharification of hydrothermally pretreated straw

BACKGROUND

Wheat straw forms an important, reliable source of lignocellulosic biomass for use in second-generation ethanol production. However, there is limited understanding of the variation in quality of straw from current breeding cultivars, and studies on such variation have generally employed suboptimal pretreatments. There is also a degree of confusion regarding phenotypic characteristics relevant to optimising the enzymatic saccharification of cellulose after suitable pretreatments for biorefining compared with those which determine good ruminant digestibility. The aim of this study has been to (a) evaluate and compare the levels of glucose enzymatically released from straw obtained from 89 cultivars of winter wheat after optimised hydrothermal pretreatments and (b) identify the underlying phenotypic characteristics relevant to enhanced glucose production with special reference to the ratios of constituent tissue types.

RESULTS

Optimised pretreatment involved hydrothermal extraction at 210 °C for 10 min. Using excess cellulases, quantitative saccharification was achieved within 24 h. The amount of glucose released ranged from 192 to 275 mg/g. The extent of glucose release was correlated with (a) the level of internode tissue (R = 0.498; p = 6.84 × 10^-7), (b) stem height (R = 0.491; p = 1.03 × 10^-6), and (c) chemical characteristics particular to stem tissues including higher levels of cellulose (R = 0.552; p = 2.06 × 10^-8) and higher levels of lignin R = 0.494; p = 8.67 × 10^-7.

CONCLUSIONS

In order to achieve maximum yields of cellulosic glucose for second-generation ethanol production, a predisposition for wheat to produce cellulose-enriched internode stem tissue, particularly of longer length, would be beneficial. This contrasts with the ideotype for ruminant nutrition, in which an increased proportion of leaf tissue is preferable.

Feedstock selection for polymer and chemical production: feedstock-specific recalcitrance

Plant cell wall materials derived from a range of waste biomass sources have great potential as a source of sustainable alternatives to petrochemicals. Perhaps the most straightforward way of realising this potential would be to hydrolyse the most efficiently fermentable polymers into their constituent sugars and use yeast to ferment these into useful chemicals. However, it also makes sense to pre-extract components which have a greater value in polymeric form. This is particularly true for non-cellulosic polymers, which are rich in poorly-fermentable pentose sugars. Liquid hot water (LHW) pretreatment can be used to extract non-cellulosic carbohydrates in a cost-effective manner, leaving a cellulose-rich substrate which is easier to hydrolyse using commercial cellulases. However, inherent differences in the plant cell wall structure and composition mean that some biomass sources may be more suitable for exploitation than others. Here, we examine eight different feedstocks (two each from hardwood, softwood, cereal straws and dicotyledonous crops), expose them to 26 different LHW pretreatment conditions and hydrolyse the entire pretreated slurry with a commercial cellulase. This enables side-by-side comparisons, in terms of saccharification yield, of the feedstocks. The results clearly demonstrate considerable differences in suitability between the feedstocks, in relation to the quantity of products released and the processes needed to obtain them.

Carbohydrate microarrays and their use for the identification of molecular markers for plant cell wall composition

Genetic improvement of the plant cell wall has enormous potential to increase the quality of food, fibers, and fuels. However, the identification and characterization of genes involved in plant cell wall synthesis is far from complete. Association mapping is one of the few techniques that can help identify candidate genes without relying on our currently incomplete knowledge of cell wall synthesis. However, few cell wall phenotyping methodologies have proven sufficiently precise, robust, or scalable for association mapping to be conducted for specific cell wall polymers. Here, we created high-density carbohydrate microarrays containing chemically extracted cell wall polysaccharides collected from 331 genetically diverse Brassica napus cultivars and used them to obtain detailed, quantitative information describing the relative abundance of selected noncellulosic polysaccharide linkages and primary structures. We undertook genome-wide association analysis of data collected from 57 carbohydrate microarrays and identified molecular markers reflecting a diversity of specific xylan, xyloglucan, pectin, and arabinogalactan moieties. These datasets provide a detailed insight into the natural variations in cell wall carbohydrate moieties between B. napus genotypes and identify associated markers that could be exploited by marker-assisted breeding. The identified markers also have value beyond B. napus for functional genomics, facilitated by the close genetic relatedness to the model plant Arabidopsis Together, our findings provide a unique dissection of the genetic architecture that underpins plant cell wall biosynthesis and restructuring.

Recent applications of metabolomics to advance microbial biofuel production

Biofuel production from plant biomass is a promising source of renewable energy [1]. However, efficient biofuel production involves the complex task of engineering high-performance microorganisms, which requires detailed knowledge of metabolic function and regulation. This review highlights the potential of mass-spectrometry-based metabolomic analysis to guide rational engineering of biofuel-producing microbes. We discuss recent studies that apply knowledge gained from metabolomic analyses to increase the productivity of engineered pathways, characterize the metabolism of emerging biofuel producers, generate novel bioproducts, enable utilization of lignocellulosic feedstock, and improve the stress tolerance of biofuel producers.

Fast enhancement on bondability of wheat straw surface for bio-composites manufacture via dielectric barrier discharge plasma

The increased roughness, improved wettability, and enhanced polarity after plasma treatment have responsibility for the enhancement on bondability of bio-composite.

Effect of Brassica napus cultivar on cellulosic ethanol yield

BACKGROUND

Intraspecific variations in biomass composition are likely to influence their suitability for biorefining. This may be particularly important in species such as Brassica napus, which contain many different crop types bred for different purposes. Here, straw derived from 17 B. napus cultivars, of varying crop types, were steam exploded, saccharified and fermented to establish differences in biomass composition relevant to cellulosic ethanol production.

RESULTS

Despite being grown and processed in the same manner, straw from the various cultivars produced different saccharification and fermentation yields after processing. Fermentation inhibitor abundances released by steam explosion also varied between genotypes. Cultivars with glucan-rich straw did not necessarily produce higher saccharification or ethanol yields after processing. Instead, the compositions of non-cellulosic components were more reliable indicators of substrate quality. The abundance of pectins and arabinogalactans had the greatest influence on saccharification efficiency between straw genotypes.

CONCLUSIONS

In dicotyledonous species, such as B. napus, variations in the abundance of pectins between crop cultivars are likely to influence processing efficiency for bioethanol production. Knowledge of these genotypic variants provides targets for plant breeding and could aid in the development of improved cellulase cocktails.

Characterization of cell wall components of wheat bran following hydrothermal pretreatment and fractionation

BACKGROUND

Pretreatments are a prerequisite for enzymatic hydrolysis of biomass and production of ethanol. They are considered to open up the plant cell wall structure by altering, moving or solubilizing lignin and hydrolyzing a proportion of hemicellulosic moieties. However, there is little information concerning pretreatment-induced changes on wheat bran cell wall polymers and indeed on changes in cell wall phenolic esters in bran or other lignocellulosic biomass. Here, we evaluate polymeric changes (chemical and physical) as a result of selected hydrothermal pretreatment conditions on destarched wheat bran using controlled polymer extraction methods. Quantification of cell wall components together with soluble oligosaccharides, the insoluble residues and ease of extractability and fractionation of biomass residues were conducted.

RESULTS

Pretreatment solubilized selected arabinoxylans and associated cross-linking ferulic and diferulic acids with a concomitant increase in lignin and cellulosic glucose. The remaining insoluble arabinoxylans were more readily extractable in alkali and showed considerable depolymerization. The degree of arabinose substitution was less in xylans released by higher concentrations of alkali. The recalcitrant biomass which remained after pretreatment and alkali extraction contained mostly cellulosic glucose and Klason lignin. Pretreatment generated small but insignificant amounts of yeast-inhibiting compounds such as furfural and hydroxymethyl furfural. As such, simultaneous saccharification and fermentation of the hydrothermally pretreated bran resulted in increased ethanol yields compared to that of the control (97.5% compared to 63% theoretical).

CONCLUSION

Hydrothermal pretreatment of destarched wheat bran resulted in degradation and depolymerization of the hemicellulosic arabinoxylans together with some breakdown of cellulosic glucose. This was accompanied by a significant reduction in the cross-linking phenolic acids such as ferulic and diferulic acids. The results suggest that hydrothermal pretreatment enhances enzymatic digestibility of the cellulose not only by depolymerization and solubilization of the hemicelluloses but by breakdown of interpolymeric phenolic cross-links between the remaining insoluble polymers. This allows easier access of hydrolytic enzymes by opening or loosening of the cell wall thus resulting in enhanced saccharification of cellulose and subsequent fermentation to ethanol. The reduction in cinnamic acids by selected breeding or biotechnological approaches could provide a useful basis for improved saccharification and fractionation of wheat bran polysaccharides.