What cell wall components are the best indicators for Miscanthus digestibility and conversion to ethanol following variable pretreatments?

Exploring the Bioethanol Production Potential of Miscanthus Cultivars

Miscanthus is a fast-growing perennial grass that attracts significant attention for its potential application as a feedstock for bioethanol production. This report explores the difference in the lignocellulosic composition of various Miscanthus cultivars, including Miscanthus × giganteus cultivated at the same location (mainly Lincoln, UK). It also assesses the sugar release profiles and mineral composition profiles of five Miscanthus cultivars harvested over a growing period from November 2018 to February 2019. The results showed that Miscanthus × giganteus contains approximately 45.5% cellulose, 29.2% hemicellulose and 23.8% lignin (dry weight, w/w). Other cultivars of Miscanthus also contain high quantities of carbohydrates (cellulose 41.1–46.0%, hemicellulose 24.3–32.6% and lignin 21.4–24.9%). Pre-treatment of Miscanthus using dilute acid followed by enzymatic hydrolysis released 63.7–80.2% of the theoretical glucose content. Fermentation of a hydrolysate of Miscanthus × giganteus using Saccharomyces cerevisiae NCYC2592 produced 13.58 ± 1.11 g/L of ethanol from 35.13 ± 0.46 g/L of glucose, corresponding to a yield of 0.148 g/g dry weight Miscanthus biomass. Scanning electron microscopy was used to study the morphology of raw and hydrolysed Miscanthus samples, which provided visual proof of Miscanthus lignocellulose degradation in these processes. The sugar release profile showed that a consequence of Miscanthus plant growth is an increase in difficulty in releasing monosaccharides from the biomass. The potassium, magnesium, sodium, sulphur and phosphorus contents in various Miscanthus cultivars were analysed. The results revealed that these elements were slowly lost from the plants during the latter part of the growing season, for a specific cultivar, until February 2019.

Breeding Targets to Improve Biomass Quality in Miscanthus

Lignocellulosic crops are attractive bioresources for energy and chemicals production within a sustainable, carbon circular society. Miscanthus is one of the perennial grasses that exhibits great potential as a dedicated feedstock for conversion to biobased products in integrated biorefineries. The current biorefinery strategies are primarily focused on polysaccharide valorization and require severe pretreatments to overcome the lignin barrier. The need for such pretreatments represents an economic burden and impacts the overall sustainability of the biorefinery. Hence, increasing its efficiency has been a topic of great interest. Inversely, though pretreatment will remain an essential step, there is room to reduce its severity by optimizing the biomass composition rendering it more exploitable. Extensive studies have examined the miscanthus cell wall structures in great detail, and pinpointed those components that affect biomass digestibility under various pretreatments. Although lignin content has been identified as the most important factor limiting cell wall deconstruction, the effect of polysaccharides and interaction between the different constituents play an important role as well. The natural variation that is available within different miscanthus species and increased understanding of biosynthetic cell wall pathways have specified the potential to create novel accessions with improved digestibility through breeding or genetic modification. This review discusses the contribution of the main cell wall components on biomass degradation in relation to hydrothermal, dilute acid and alkaline pretreatments. Furthermore, traits worth advancing through breeding will be discussed in light of past, present and future breeding efforts.

The effects of fiber source on extrusion processing parameters and kibble characteristics of dry cat foods

Cellulose and beet pulp have been commonly used in the pet food industry to increase the dietary fiber content of cat foods. However, pet food companies seek alternatives to these so-called byproducts. Miscanthus grass is grown for its fiber content and may serve as an alternative to traditional fibrous ingredients. The objectives of this study were to determine the effects of fiber sources on extrusion processing and kibble structure of cat foods. Three replicate batches of a complete and balanced foods for adult cats at maintenance each containing 10% of Miscanthus grass, cellulose, or beet pulp was mixed and kibbles were produced on a single-screw extruder. Feed rate, preconditioner water and steam, extruder screw speed, extruder water and steam addition, and knife speed were adjusted to achieve a wet bulk density of 330 g/L. After extrusion, kibbles were dried at 115.5 ºC to less than 10% moisture. Dried kibbles were coated with chicken fat and flavor enhancer. No effects due to fiber source were reported for extrusion parameters or kibble measurements (P > 0.05) with the exception of compression energy, wherein kibbles produced with cellulose required more energy to compress than those containing beet pulp (6,917 N mm vs. 3,591 N mm, respectively). In conclusion, tested fiber sources had no impact on extrusion parameters and most kibble characteristics. Kibbles containing cellulose required more energy to compress than kibbles containing beet pulp. Miscanthus grass could be used as an alternative to traditional fiber sources used to produce cat foods.

Radiation-Induced Structural Changes of Miscanthus Biomass

Efficient pretreatment is a prerequisite for lignocellulosic biomass biorefinery due to the structure of lignocellulose. This study is a first-time investigation into the structural changes of Miscanthus biomass treated with 60Co γ-ray irradiation in different doses up to 1200 kGy. The structural properties of the treated sample have been systematically characterized by FTIR, thermogravimetric analysis (TGA), XRD, gel permeation chromatography (GPC), a laser particle size analyzer, SEM, an atomic force microscope (AFM), and NMR. The results show that irradiation treatment can partially destroy the intra- or inter-molecular hydrogen bonds of biomass. Irradiation treatment can also reduce particle size, narrow the distribution range, as well as increase the specific surface area of biomasses. Noticeably, the TGA stability of the treated biomass decreases with increasing absorbed doses. To respond to these structural changes, the treated biomass can be easily hydrolyzed by cellulases with a high yield of reducing sugars (557.58 mg/g biomass), much higher than that of the untreated sample. We conclude that irradiation treatment can damage biomass structure, a promising strategy for biomass biorefinery in the future.

Effect of fiber source and particle size on chick performance and nutrient utilization

The addition of fiber in chick feeds is known to dilute nutrients; as a result, this may reduce nutrient digestibility and performance. However, recent studies suggest that moderate inclusion of insoluble fibers (2 to 3%) may stimulate gizzard development, which could result in better nutrient utilization and chick growth. The previous fiber sources evaluated were subject to wide fluctuation in their nutritional and chemical composition due to variation in processing. Miscanthus giganteus is a C4 grass purposefully grown for its fiber content which has a consistent fiber composition compared to food process residues. The objectives of this study were to determine the effect of dietary fiber source and particle size on day-old chick performance and nutrient digestibility. Day-old chicks (8 chicks per cage, 5 cages per treatment) were fed diets containing 3% of either sepiolite (SEP), cellulose (CEL), coarse beet pulp (BP), fine BP, coarse Miscanthus grass (MG), and fine MG. At the end of days 7, 14, and 21, chicks and experimental diets were weighed to compute average daily gain and feed intake. In addition, excreta from the previous 48 h of each data capture point was collected to determine nutrient digestibility. In general, chicks fed diets containing fiber consumed more feed, gained more weight, and had better feed conversion rate than birds fed the SEP diet. Particle size of the fiber had no effect on chick performance; however, nutrient utilization was higher (P < 0.05) for chicks fed coarse fiber particles compared to these fed fine fiber particles. Birds fed diets containing MG performed similar to chicks fed CEL (P > 0.05), but digestibility coefficients of birds fed BP diets were generally higher than chicks fed MG diets. In conclusion, chicks performed better with fiber in their diet and MG was comparable to CEL.

The effects of diets varying in fibre sources on nutrient utilization, stool quality and hairball management in cats

Pet food companies use fibrous ingredients in cat foods to aid weight and hairball management. Miscanthus grass could be an alternative novel fibre source for cat foods. The objectives of this work were to determine the effects of Miscanthus grass as a fibre source on nutrient utilization, stool quality and hairball management in cats. Dry extruded cat foods (average chemical composition; digestibility trial: 94.54% dry matter-DM, 34.47% crude protein-CP, 11.67% crude fat, 7.06% ash and 13.04% total dietary fibre-TDF; and hairball trial: 94.88% DM, 34.60% CP, 11.30% crude fat, 7.02% ash and 9.77% TDF) were fed to 12 cats for a 9-day (digestibility trial) or 16-day (hairball trial) adaptation period followed by a 5-day total faecal collection period. Digestibility trial was performed as a replicated Latin square design, and the hairball trial was performed as a switchback design. In general, the cats fed the beet pulp diet (BPD) had higher DM, organic matter, gross energy and TDF digestibility than cats fed Miscanthus grass (MGD) or cellulose (CED) diet (p < .05). However, CP digestibility was lower for cats fed BPD (82.1 vs. 84.7 and 85.1%, respectively, for BPD, MGD and CED). These differences could be due to the differences in dietary fibre content and(or) composition. Faecal scores were lower for cats fed BPD (2.84) compared with MGD (3.32) and CED (3.21; p < .05). No effects due to fibre were reported on the faecal hairball variables, with the exception of less total hair weight and hair clumps per gram of dry faeces for cats fed Miscanthus grass (MGH) compared with control diet (COH; p < .05). In conclusion, Miscanthus grass could be used as an alternative ingredient to cellulose in cat diets.

The in vivo impact of MsLAC1, a Miscanthus laccase isoform, on lignification and lignin composition contrasts with its in vitro substrate preference

BACKGROUND

Understanding lignin biosynthesis and composition is of central importance for sustainable bioenergy and biomaterials production. Species of the genus Miscanthus have emerged as promising bioenergy crop due to their rapid growth and modest nutrient requirements. However, lignin polymerization in Miscanthus is poorly understood. It was previously shown that plant laccases are phenol oxidases that have multiple functions in plant, one of which is the polymerization of monolignols. Herein, we link a newly discovered Miscanthus laccase, MsLAC1, to cell wall lignification. Characterization of recombinant MsLAC1 and Arabidopsis transgenic plants expressing MsLAC1 were carried out to understand the function of MsLAC1 both in vitro and in vivo.

RESULTS

Using a comprehensive suite of molecular, biochemical and histochemical analyses, we show that MsLAC1 localizes to cell walls and identify Miscanthus transcription factors capable of regulating MsLAC1 expression. In addition, MsLAC1 complements the Arabidopsis lac4-2 lac17 mutant and recombinant MsLAC1 is able to oxidize monolignol in vitro. Transgenic Arabidopsis plants over-expressing MsLAC1 show higher G-lignin content, although recombinant MsLAC1 seemed to prefer sinapyl alcohol as substrate.

CONCLUSIONS

In summary, our results suggest that MsLAC1 is regulated by secondary cell wall MYB transcription factors and is involved in lignification of xylem fibers. This report identifies MsLAC1 as a promising breeding target in Miscanthus for biofuel and biomaterial applications.

The effects on nutrient utilization and stool quality of Beagle dogs fed diets with beet pulp, cellulose, and Miscanthus grass12

Dogs can benefit from dietary fibers. Traditionally, cellulose (CE) and beet pulp (BP) have been used by pet food companies as insoluble and soluble fiber sources. Miscanthus grass (MG) is a novel fiber ingredient made from Miscanthus giganteus, a C4 grass produced for its fiber content, but it has not been evaluated for dogs. The objectives of this study were to determine the effects of different fiber sources on nutrient utilization and stool consistency by dogs. Twelve Beagle dogs were fed 3 dietary treatments varying in their fiber sources (BP, CE, MG). Diets were fed for a 14-d period (9 d adaptation), fecal samples were collected (5 d total fecal collection) and scored. Nutrient digestibility was estimated using total fecal collection (TFC). Dogs fed BP diet had softer stools than dogs fed CE and MG (3.15 vs. 3.68 and 3.64, respectively). Wet fecal output was higher for dogs fed CE compared to MG, with dogs fed BP having the lowest values (254.3 g vs. 241.6 g vs. 208.5 g, respectively). Dogs fed CE and MG had lower DM digestibility than dogs fed BP (P < 0.05), dogs fed BP had lower CP digestibility compared with dogs fed MG and CE (81.4% vs. 85.5% and 85.8%, respectively). In conclusion, MG could be used as an alternative fiber source to CE.

Tracking of enzymatic biomass deconstruction by fungal secretomes highlights markers of lignocellulose recalcitrance

BACKGROUND

Lignocellulose biomass is known as a recalcitrant material towards enzymatic hydrolysis, increasing the process cost in biorefinery. In nature, filamentous fungi naturally degrade lignocellulose, using an arsenal of hydrolytic and oxidative enzymes. Assessment of enzyme hydrolysis efficiency generally relies on the yield of glucose for a given biomass. To better understand the markers governing recalcitrance to enzymatic degradation, there is a need to enlarge the set of parameters followed during deconstruction.

RESULTS

Industrially-pretreated biomass feedstocks from wheat straw, miscanthus and poplar were sequentially hydrolysed following two steps. First, standard secretome from Trichoderma reesei was used to maximize cellulose hydrolysis, producing three recalcitrant lignin-enriched solid substrates. Then fungal secretomes from three basidiomycete saprotrophs (Laetisaria arvalis, Artolenzites elegans and Trametes ljubarskyi) displaying various hydrolytic and oxidative enzymatic profiles were applied to these recalcitrant substrates, and compared to the T. reesei secretome. As a result, most of the glucose was released after the first hydrolysis step. After the second hydrolysis step, half of the remaining glucose amount was released. Overall, glucose yield after the two sequential hydrolyses was more dependent on the biomass source than on the fungal secretomes enzymatic profile. Solid residues obtained after the two hydrolysis steps were characterized using complementary methodologies. Correlation analysis of several physico-chemical parameters showed that released glucose yield was negatively correlated with lignin content and cellulose crystallinity while positively correlated with xylose content and water sorption. Water sorption appears as a pivotal marker of the recalcitrance as it reflects chemical and structural properties of lignocellulosic biomass.

CONCLUSIONS

Fungal secretomes applied to highly recalcitrant biomass samples can further extend the release of the remaining glucose. The glucose yield can be correlated to chemical and physical markers, which appear to be independent from the biomass type and secretome. Overall, correlations between these markers reveal how nano-scale properties (polymer content and organization) influence macro-scale properties (particle size and water sorption). Further systematic assessment of these markers during enzymatic degradation will foster the development of novel cocktails to unlock the degradation of lignocellulose biomass.