Optimization of pullulan production by Aureobasidium pullulans using semi-solid-state fermentation and artificial neural networks: Characterization and antibacterial activity of pullulan impregnated with Ag-TiO2 nanocomposite

This study presents a novel and efficient approach for pullulan production using artificial neural networks (ANNs) to optimize semi-solid-state fermentation (S-SSF) on faba bean biomass (FBB). This method achieved a record-breaking pullulan yield of 36.81 mg/g within 10.82 days, significantly exceeding previous results. Furthermore, the study goes beyond yield optimization by characterizing the purified pullulan, revealing its unique properties including thermal stability, amorphous structure, and antioxidant activity. Energy-dispersive X-ray spectroscopy and scanning electron microscopy confirmed its chemical composition and distinct morphology. This research introduces a groundbreaking combination of ANNs and comprehensive characterization, paving the way for sustainable and cost-effective pullulan production on FBB under S-SSF conditions. Additionally, the study demonstrates the successful integration of pullulan with Ag@TiO2 nanoparticles during synthesis using Fusarium oxysporum. This novel approach significantly enhances the stability and efficacy of the nanoparticles by modifying their surface properties, leading to remarkably improved antibacterial activity against various human pathogens. These findings showcase the low-cost production medium, and extensive potential of pullulan not only for its intrinsic properties but also for its ability to significantly improve the performance of nanomaterials. This breakthrough opens doors to diverse applications in various fields.

Extraction, recovery, and characterization of lignin from industrial corn stover lignin cake

Lignin utilization in value-added co-products is an important component of enabling cellulosic biorefinery economics. However, aqueous dilute acid pretreatments yield lignins with limited applications due to significant modification during pretreatment, low solubility in many solvents, and high content of impurities (ash, insoluble polysaccharides). This work addresses these challenges and investigates the extraction and recovery of lignins from lignin-rich insoluble residue following dilute acid pretreatment and enzymatic hydrolysis of corn stover using three extraction approaches: ethanol organosolv, NaOH, and an ionic liquid. The recovered lignins exhibited recovery yields ranging from 30% for the ionic liquid, 44% for the most severe acid ethanol organosolv condition tested, and up to 86% for the most severe NaOH extraction condition. Finally, the fractional solubilities of different recovered lignins were assessed in a range of solvents and these solubilities were used to estimate distributions of Hildebrand and Hansen solubility parameters using a novel approach.

Facile dissolution of cellulose by superbase-derived ionic liquid using organic solvents as co-solvents at mild temperatures

Dissolving cellulose at low temperatures is a key step in its efficient utilization as a renewable resource to produce high-value-added platform chemicals and high-performance materials. Here, the potential of four aprotic organic solvents was investigated for use as co-solvents with a sustainable DBU-derived ionic liquid (SIL) for the low-temperature dissolution and regeneration of cellulose. Combined experiments, density functional theory calculations, and molecular dynamic simulations were performed. The type and amount of co-solvent were found to have a significant impact on the solubility of cellulose, the dissolution process, and the structure of regenerated cellulose. The addition of organic solvents can significantly reduce the cellulose dissolution temperature and increase the solubility. Among the solvents assessed, 40 wt% DMSO exhibited the most effective synergistic interaction with SIL, where the solubility of cellulose was 14.6 wt% at 75 °C. Subsequently, the effects of the different types and amounts of co-solvents on the microscopic morphology and chemical structure of regenerated cellulose were thoroughly explored. The results showed that different types of organic solvents had different effects on the microstructure of regenerated cellulose. The results may guide the manufacturing specifications of high-performance regenerated fiber materials.

Unveiling malic acid biorefinery: Comprehensive insights into feedstocks, microbial strains, and metabolic pathways

The over-reliance on fossil fuels and resultant environmental issues necessitate sustainable alternatives. Microbial fermentation of biomass for malic acid production offers a viable, eco-friendly solution, enhancing resource efficiency and minimizing ecological damage. This review covers three core aspects of malic acid biorefining: feedstocks, microbial strains, and metabolic pathways. It emphasizes the significance of utilizing biomass sugars, including the co-fermentation of different sugar types to improve feedstock efficiency. The review discusses microbial strains for malic acid fermentation, addressing challenges related to by-products from biomass breakdown and strategies for overcoming them. It delves into the crucial pathways and enzymes for malic acid production, outlining methods to optimize its metabolism, focusing on enzyme regulation, energy balance, and yield enhancement. These insights contribute to advancing the field of consolidated bioprocessing in malic acid biorefining.

Sustainable biorefining and bioprocessing of green seaweed (Ulva spp.) for the production of edible (ulvan) and non-edible (polyhydroxyalkanoate) biopolymeric films

A sustainable biorefining and bioprocessing strategy was developed to produce edible-ulvan films and non-edible polyhydroxybutyrate films. The preparation of edible-ulvan films by crosslinking and plasticisation of ulvan with citric acid and xylitol was investigated using Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC) analysis. The edible ulvan film was tested for its gut-friendliness using Lactobacillus and Bifidobacterium spp. (yoghurt) and was shown to improve these gut-friendly microbiome's growth and simultaneously retarding the activity of pathogens like Escherchia coli and Staphylococcus aureus. Green macroalgal biomass refused after the extraction of ulvan was biologically processed by dark fermentation to produce a maximum of 3.48 (± 0.14) g/L of volatile fatty acids (VFAs). Aerobic processing of these VFAs using Cupriavidus necator cells produced 1.59 (± 0.12) g/L of biomass with 18.2 wt% polyhydroxybutyrate. The present study demonstrated the possibility of producing edible and non-edible packaging films using green macroalgal biomass as the sustainable feedstock.

Genetic markers and tree properties predicting wood biorefining potential in aspen (Populus tremula) bioenergy feedstock

BACKGROUND

Wood represents the majority of the biomass on land and constitutes a renewable source of biofuels and other bioproducts. However, wood is recalcitrant to bioconversion, raising a need for feedstock improvement in production of, for instance, biofuels. We investigated the properties of wood that affect bioconversion, as well as the underlying genetics, to help identify superior tree feedstocks for biorefining.

RESULTS

We recorded 65 wood-related and growth traits in a population of 113 natural aspen genotypes from Sweden ( https://doi.org/10.5061/dryad.gtht76hrd ). These traits included three growth and field performance traits, 20 traits for wood chemical composition, 17 traits for wood anatomy and structure, and 25 wood saccharification traits as indicators of bioconversion potential. Glucose release after saccharification with acidic pretreatment correlated positively with tree stem height and diameter and the carbohydrate content of the wood, and negatively with the content of lignin and the hemicellulose sugar units. Most of these traits displayed extensive natural variation within the aspen population and high broad-sense heritability, supporting their potential in genetic improvement of feedstocks towards improved bioconversion. Finally, a genome-wide association study (GWAS) revealed 13 genetic loci for saccharification yield (on a whole-tree-biomass basis), with six of them intersecting with associations for either height or stem diameter of the trees.

CONCLUSIONS

The simple growth traits of stem height and diameter were identified as good predictors of wood saccharification yield in aspen trees. GWAS elucidated the underlying genetics, revealing putative genetic markers for bioconversion of bioenergy tree feedstocks.

Biosynthesis of artificial starch and microbial protein from agricultural residue

Growing populations and climate change pose great challenges to food security. Humankind is confronting a serious question: how will we feed the world in the near future? This study presents an out-of-the-box solution involving the highly efficient biosynthesis of artificial starch and microbial proteins from available and abundant agricultural residue as new feed and food sources. A one-pot biotransformation using an in vitro coenzyme-free synthetic enzymatic pathway and baker's yeast can simultaneously convert dilute sulfuric acid-pretreated corn stover to artificial starch and microbial protein under aerobic conditions. The β-glucosidase-free commercial cellulase mixture plus an ex vivo two-enzyme complex containing cellobiose phosphorylase and potato α-glucan phosphorylase displayed on the surface of Saccharomyces cerevisiae, showed better cellulose hydrolysis rates than a commercial β-glucosidase-rich cellulase mixture. This is because the channeling of the hydrolytic product from the solid cellulosic feedstock to the yeast mitigated the inhibition of the cellulase cocktail. Animal tests have shown that the digestion of artificial amylose results in slow and relatively small changes in blood sugar levels, suggesting that it could be a new health food component that prevents obesity and diabetes. A combination of the utilization of available agricultural residue and the biosynthesis of starch and microbial protein from non-food biomass could address the looming food crisis in the food-energy-water nexus.

Combination of genetic engineering and random mutagenesis for improving production of raw-starch-degrading enzymes in Penicillium oxalicum

BACKGROUND

Raw starch-degrading enzyme (RSDE) is applied in biorefining of starch to produce biofuels efficiently and economically. At present, RSDE is obtained via secretion by filamentous fungi such as Penicillium oxalicum. However, high production cost is a barrier to large-scale industrial application. Genetic engineering is a potentially efficient approach for improving production of RSDE. In this study, we combined genetic engineering and random mutagenesis of P. oxalicum to enhance RSDE production.

RESULTS

A total of 3619 mutated P. oxalicum colonies were isolated after six rounds of ethyl methanesulfonate and Co⁶⁰-γ-ray mutagenesis with the strain A2-13 as the parent strain. Mutant TE4-10 achieved the highest RSDE production of 218.6 ± 3.8 U/mL with raw cassava flour as substrate, a 23.2% compared with A2-13. Simultaneous deletion of transcription repressor gene PoxCxrC and overexpression of activator gene PoxAmyR in TE4-10 resulted in engineered strain GXUR001 with an RSDE yield of 252.6 U/mL, an increase of 15.6% relative to TE4-10. Comparative transcriptomics and real-time quantitative reverse transcription PCR revealed that transcriptional levels of major amylase genes, including raw starch-degrading glucoamylase gene PoxGA15A, were markedly increased in GXUR001. The hydrolysis efficiency of raw flour from cassava and corn by crude RSDE of GXUR001 reached 93.0% and 100%, respectively, after 120 h and 84 h with loading of 150 g/L of corresponding substrate.

CONCLUSIONS

Combining genetic engineering and random mutagenesis efficiently enhanced production of RSDE by P. oxalicum. The RSDE-hyperproducing mutant GXUR001 was generated, and its crude RSDE could efficiently degrade raw starch. This strain has great potential for enzyme preparation and further genetic engineering.

Recent developments in biorefining of macroalgae metabolites and their industrial applications - A circular economy approach

The macroalgal industry is expanding, and the quest for novel ingredients to improve and develop innovative products is crucial. Consumers are increasingly looking for natural-derived ingredients in cosmetic products that have been proven to be effective and safe. Macroalgae-derived compounds have growing popularity in skincare products as they are natural, abundant, biocompatible, and renewable. Due to their high biomass yields, rapid growth rates, and cultivation process, they are gaining widespread recognition as potentially sustainable resources better suited for biorefinery processes. This review demonstrates macroalgae metabolites and their industrial applications in moisturizers, anti-aging, skin whitening, hair, and oral care products. These chemicals can be obtained in combination with energy products to increase the value of macroalgae from an industrial perspective with a zero-waste approach by linking multiple refineries. The key challenges, bottlenecks, and future perspectives in the operation and outlook of macroalgal biorefineries were also discussed.

Xylo-oligosaccharides, fermentable sugars, and bioenergy production from sugarcane straw using steam explosion pretreatment at pilot-scale

This study investigated the production of xylo-oligosaccharides (XOS) from sugarcane straw (SCS) using steam explosion (SE) pretreatment at pilot-scale, as well as co-production of fermentable sugars and lignin-rich residues for bioethanol and bioenergy, respectively. SE conditions 200 °C; 15 bar; 10 min led to 1) soluble XOS yields of up to 35 % (w/w) of initial xylan with ∼50 % of the recovered XOS corresponding to xylobiose and xylotriose, considered the most valuable sugars for prebiotic applications; 2) fermentable glucose yields from the enzymatic hydrolysis of SE-pretreated SCS of up to ∼78 %; 3) increase in the energy content of saccharified SCS residues (16 %) compared to the untreated material. From an integrated biorefinery perspective, it demonstrated the potential use of SCS for the production of value-added XOS ingredients as well as liquid and solid biofuel products.

Fermentative volatile fatty acid production and recovery from grass using a novel combination of solids separation, pervaporation, and electrodialysis technologies

A novel combination of solids screening, centrifugation, microfiltration, pervaporation, and electrodialysis were used for the targeted and exclusive recovery of volatile fatty acids (VFAs) from an 80L bioreactor. The bioreactor was continually-fed with grass waste, containing 40gL^-1 total solids, over three, seven-day, hydraulic retention times. A VFA solution with a concentration up to 4,500 mgL^-1 was recovered. VFA yields were also increased from 707 to 875 mg of VFA per gram of volatile solids by alleviating end-product inhibition. Both these accomplishments are significant step-changes in adding value to waste, and increased substrate utilisation rates will be attractive from a waste remediation perspective.

Room temperature dissolving cellulose with a metal salt hydrate-based deep eutectic solvent

Abundant and renewable cellulose is a potential candidate for petroleum-derived synthetic polymers. However, the efficient dissolution of this material is problematic because of the high cost, severe reaction condition (e.g., high temperature) and environmentally unfriendly (e.g., toxic reagents, and solvent recyclability). Herein, to realize the room temperature dissolution of cellulose with an inexpensive and eco-friendly solvent, we design a novel low-cost deep eutectic solvent that is composed of zinc chloride, water and phosphoric acid for the efficient dissolution of cellulose. This solvent is featured as having both the superior hydrogen bonding acidity and the hydrogen bonding basicity, and thus can act as a hydrogen bond molecular scissors to cleave the hydrogen bonds within cellulose. In this process, microcrystalline cellulose can be easily dissolved in the solvent at room temperature with a dissolution ratio up to 15 wt%. The dissolved cellulose can also be recovered without any derivatization. The universality, recyclability and pilot production of dissolving cellulose using this solvent are also demonstrated. This work provides a new strategy for the design of novel deep eutectic solvent capable of disrupting the hydrogen bonds of cellulose under mild conditions.

Review of advances in the development of laccases for the valorization of lignin to enable the production of lignocellulosic biofuels and bioproducts

Development and deployment of commercial biorefineries based on conversion of lignocellulosic biomass into biofuels and bioproducts faces many challenges that must be addressed before they are commercially viable. One of the biggest challenges faced is the efficient and scalable valorization of lignin, one of the three major components of the plant cell wall. Lignin is the most abundant aromatic biopolymer on earth, and its presence hinders the extraction of cellulose and hemicellulose that is essential to biochemical conversion of lignocellulose to fuels and chemicals. There has been a significant amount of work over the past 20 years that has sought to develop innovative processes designed to extract and recycle lignin into valuable compounds and help reduce the overall costs of the biorefinery process. Due to the complex matrix of lignin, which is essential for plant survival, the development of a reliable and efficient lignin conversion technology has been difficult to achieve. One approach that has received significant interest relies on the use of enzymes, notably laccases, a class of multi‑copper green oxidative enzymes that catalyze bond breaking in lignin to produce smaller oligomers. In this review, we first assess the different innovations of lignin valorization using laccases within the context of a biorefinery process, and then assess the latest economical advances that these innovations offered. Finally, we review laccase characterization and optimization, as well as the prospects and bottlenecks of this class of enzymes within the industrial and biorefining sectors.

Process development for tall oil lignin production

The aim of this work was to study the production and characterization of tall oil lignin (TOL) from tall oil soap (TOS) of the kraft pulping process following a new process (i.e., LignoTall). Also, the properties of the TOL and kraft lignin (KL) produced via LignoForce technology were compared. Although TOL and KL were generated from the same black liquor and softwood species, they had remarkably different characteristics, confirming the impact of the production methods on the physicochemical properties of the isolated lignin. TOL had higher molecular weight, O/C elemental ratio, sulfur content, and carboxylate-OH content but lower methoxy group content than did KL. The high sulfur group content (7.3%) of TOL can be very useful for the vulcanization process. Moreover, the high carboxylate-OH content of TOL (0.56 mmol/g) is desirable for its utilization in epoxy resin production.

Bio-processing of macroalgae Palmaria palmata: metabolite fractionation from pressed fresh material and ensiling considerations for long-term storage

Red algae, belonging to the phylum Rhodophyta, contain an abundance of useful chemicals including bioactive molecules and present opportunities for the production of different products through biorefinery cascades. The rhodophyte Palmaria palmata, commonly termed dulse or dillisk, grows predominantly on the northern coasts of the Atlantic and Pacific Oceans and is a well-known snack food. Due to its abundance, availability and cultivation capacity, P. palmata was selected for study as a potential candidate for a biorefinery process. In addition to studying juice and solid fractions of freshly harvested P. palmata, we have investigated the novel possibility of preserving algal biomass by ensilaging protocols similar to those employed for terrestrial forage crops. In the metabolite partitioning within the solid and liquid fractions following screw-pressing, the majority of the metabolites screened for-water soluble carbohydrates, proteins and amino acids, lipids, pigments, phenolics and antioxidant activity-remained in the solid fraction, though at differing proportions depending on the metabolite, from 70.8% soluble amino acids to 98.2% chlorophyll a and 98.1% total carotenoids. For the ensiling study, screw-pressed P. palmata, with comparative wilted and chopped, and chopped only samples, were ensiled at scale with and without Safesil silage additive. All samples were successfully ensiled after 90 days, with screw-pressing giving lower or equal pH before and after ensiling compared with the other preparations. Of particular note was the effluent volumes generated during ensiling: 26-49% of the fresh weight, containing 16-34% of the silage dry matter. This may be of advantage depending on the final use of the biomass.

Phosphorylated kraft lignin with improved thermal stability

The low cost, environmental friendliness, and reproducibility of kraft lignin (KL) make it a potential candidate for the development of new green material. The phosphorylation of KL can extend its application as a flame-retardant material. Herein, the phosphorylated kraft lignin (PKL) was systematically fabricated in a sustainable process by utilizing a green phosphating reagent, NH₄H₂PO₄, in the presence of urea. The influence of the reaction parameters, i.e., reaction time and temperature, and NH₄H₂PO₄/lignin ratio on the phosphorylation process were investigated. Advanced characterization techniques including ¹H NMR, ³¹P NMR, and XPS confirmed that the phosphorus groups were successfully introduced to lignin molecules. The active phenolic and aliphatic hydroxy groups of kraft lignin underwent a nucleophilic substitution reaction with the phosphate group to generate phosphorylated lignin. Compared with KL, PKL showed excellent thermal stability, and its maximum decomposition temperature was 620 °C compared with 541 °C for KL.

Pilot-scale production of xylo-oligosaccharides and fermentable sugars from Miscanthus using steam explosion pretreatment

This study investigated pilot-scale production of xylo-oligosaccharides (XOS) and fermentable sugars from Miscanthus using steam explosion (SE) pretreatment. SE conditions (200 °C; 15 bar; 10 min) led to XOS yields up to 52 % (w/w of initial xylan) in the hydrolysate. Liquid chromatography-mass spectrometry demonstrated that the solubilised XOS contained bound acetyl- and hydroxycinnamate residues, physicochemical properties known for high prebiotic effects and anti-oxidant activity in nutraceutical foods. Enzymatic hydrolysis of XOS-rich hydrolysate with commercial endo-xylanases resulted in xylobiose yields of 380 to 500 g/kg of initial xylan in the biomass after only 4 h, equivalent to ~74 to 90 % conversion of XOS into xylobiose. Fermentable glucose yields from enzymatic hydrolysis of solid residues were 8 to 9-fold higher than for untreated material. In view of an integrated biorefinery, we demonstrate the potential for efficient utilisation of Miscanthus for the production of renewable sources, including biochemicals and biofuels.

The use of lytic polysaccharide monooxygenases in anaerobic digestion of lignocellulosic materials

BACKGROUND

The recent discovery that LPMOs can work under anaerobic conditions when supplied with low amounts H₂O₂ opens the possibility of using LPMOs as enzyme aids in biogas reactors to increase methane yields from lignocellulosic materials. We have explored this possibility by studying anaerobic digestion of various lignocellulosic materials: Avicel, milled spruce and birch wood, and a lignin-rich hydrolysis residue from steam-exploded birch. The digestions were added LPMOs and various cellulolytic enzyme cocktails and were carried out with or without addition of H₂O₂.

RESULTS

In several cases, enzyme addition had a beneficial effect on methane production, which was partly due to components present in the enzyme preparations. It was possible to detect LPMO activity during the initial phases of the anaerobic digestions of Avicel, and in some cases LPMO activity could be correlated with improved methane production from lignocellulosic materials. However, a positive effect on methane production was only seen when LPMOs were added together with cellulases, and never upon addition of LPMOs only. Generally, the experimental outcomes showed substrate-dependent variations in process efficiency and the importance of LPMOs and added H₂O₂. These differences could relate to variations in the type and content of lignin, which again will affect the activity of the LPMO, the fate of the added H₂O₂ and the generation of potentially damaging reactive-oxygen species. The observed effects showed that the interplay between cellulases and LPMOs is important for the overall efficiency of the process.

CONCLUSION

This study shows that it may be possible to harness the power of LPMOs in anaerobic digestion processes and improve biogas production, but also highlight the complexity of the reaction systems at hand. One complicating factor was that the enzymes themselves and other organic components in the enzyme preparations acted as substrates for biogas production, meaning that good control reactions were essential to detect effects caused by enzyme activity. As also observed during regular aerobic enzymatic digestion of lignocellulosic biomass, the type and contents of lignin in the substrates likely plays a major role in determining the impact of LPMOs and of cellulolytic enzymes in general. More work is needed to unravel the interplay between LPMOs, O₂, H₂O₂, and the multitude of redox-active components found in anaerobic bioreactors degrading lignocellulosic substrates.

Upgrade of wood sugar d-xylose to a value-added nutraceutical by in vitro metabolic engineering

The upgrade of D-xylose, the most abundant pentose, to value-added biochemicals is economically important to next-generation biorefineries. myo-Inositol, as vitamin B8, has a six-carbon carbon-carbon ring. Here we designed an in vitro artificial NAD(P)-free 12-enzyme pathway that can effectively convert the five-carbon xylose to inositol involving xylose phosphorylation, carbon-carbon (C-C) rearrangement, C-C bond circulation, and dephosphorylation. The reaction conditions catalyzed by all thermostable enzymes from hyperthermophilic microorganisms Thermus thermophiles, Thermotoga maritima, and Archaeoglobus fulgidus were optimized in reaction temperature, buffer type and concentration, enzyme composition, Mg²⁺ concentration, and fed-batch addition of ATP. The 11-enzyme cocktail, whereas a fructose 1,6-bisphosphatase from T. maritima has another function of inositol monophosphatase, converted 20 mM xylose to 16.1 mM inositol with a conversion efficiency of 96.6% at 70 °C. Polyphosphate was found to replace ATP for xylulose phosphorylation due to broad substrate promiscuity of the T. maritima xylulokinase. The Tris-HCl buffer effectively mitigated the Maillard reaction at 70 °C or higher temperature. The co-production of value-added biochemicals, such as inositol, from wood sugar could greatly improve economics of new biorefineries, similar to oil refineries that make value-added plastic precursors to subsidize gasoline/diesel production.

Ionizing radiation processing and its potential in advancing biorefining and nanocellulose composite materials manufacturing

Nanocellulose is a high value material that has gained increasing attention because of its high strength, stiffness, unique photonic and piezoelectric properties, high stability and uniform structure. Through utilization of a biorefinery concept, nanocellulose can be produced in large volumes from wood at relatively low cost via ionizing radiation processing. Ionizing radiation causes significant break down of the polysaccharide and leads to the production of potentially useful gaseous products such as H2 and CO. The application of radiation processing to the production of nanocellulose from woody and non-wood sources, such as field grasses, bio-refining byproducts, industrial pulp waste, and agricultural surplus materials remains an open field, ripe for innovation and application. Elucidating the mechanisms of the radiolytic decomposition of cellulose and the mass generation of nanocellulose by radiation processing is key to tapping into this source of nanocelluose for the growth of nanocellulostic-product development. More importantly, understanding the structural break-up of the cell walls as a function of radiation exposure is a key goal and only through careful, detailed characterization and dimensional metrology can this be achieved at the level of detail that is needed to further the growth of large scale radiation processing of plant materials. This work is resulting from strong collaborations between NIST and its academic partners who are pursuing the unique demonstration of applied ionizing radiation processing to plant materials as well as the development of manufacturing metrology for novel nanomaterials.

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

BACKGROUND

Energy crops including Miscanthus provide a storable, portable energy source which can be used to complement a wide range of products and energy generation systems. Miscanthus is predominantly used in Europe as a combustion material for electricity generation but also has the potential for biochemical conversion due to its high yield and low-nutrient requirements. The ratio of holocellulose (hemicellulose and cellulose combined) to acid detergent lignin (H:L) within the senesced material has previously been shown to indicate the relative suitability of Miscanthus accessions for thermochemical conversion. In this study, the ratio was assessed to examine its use as a selection aid for biochemical conversion. 20 highly-characterised Miscanthus accessions were saccharified using an enzyme mix to determine optimum sugar release. Nine of these accessions spanning high, medium and low H:L ratios were then autoclaved with dilute acid, alkali or water, and enzymically hydrolysed and fermented to produce ethanol. Samples taken throughout the process allowed assessments of released sugars.

RESULTS

Enzymic degradation of the biomass showed a relationship between H:L ratio and glucose release, with high glucose release for high H:L ratio accessions and vice versa. Xylose release showed no such relationship. This relationship was maintained following pretreatments and enzyme saccharification, where compound analysis showed that following all pretreatments, accessions with high H:L ratios repeatedly had the highest releases of glucose, xylose and arabinose, and produced more ethanol. Release of all measured compounds increased with the pretreatment severity and ethanol yields from each pretreatment correlated with the respective glucose yield, providing assurance that any inhibitory compounds generated were tolerated by the fermentation yeast. Strong correlations were also seen between glucose release, ethanol and cell wall components, with cellulose showing the highest correlations with ethanol yields for some treatments and H:L ratio with others.

CONCLUSIONS

The H:L ratio is a good predictor of ethanol yields and sugar release from Miscanthus in this study but individual components lignin and cellulose also correlate well, especially for hot water and mild acid pretreatments. In conclusion, use of the H:L ratio does not provide any advantages over the concentration of individual cell wall components for predicting sugar release and ethanol yields.

Flocculation of thermomechanical pulping spent liquor with polydiallyldimethylammonium chloride

Currently, the dissolved lignocelluloses in the spent liquor (SL) of a thermomechanical pulping process are treated in wastewater treatment systems and thus they are wasted. In this work, polydiallyldimethylammonium chloride (PDADMAC), with different molecular weights, was used for flocculating lignocelluloses of SL and thus isolating them from SL. Results showed that the maximum removals were 38% via treating SL with 100 mg/L of PDADMAC (with 1045 kg/mol molecular weight) at 25 °C for 30 min. The focused beam reflectance measurement of the flocculation process revealed that the chord length of the flocs with the maximum square weighted counts was increased from 70 to 100 μm and also their maximum square weighted counts was increased from 5 to 25 μm²/s. The flocs contained 60.71-74.41 wt% PDADMAC, the balance of lignocelluloses and the heating value of 24-25 MJ/kg. The high molecular PDADMAC generated flocs with more organics and a higher heating value.

Supply Chain Optimisation for an Ultrasound-Organosolv Lignocellulosic Biorefinery: Impact of Technology Choices

Conversion of lignocellulose to value-added products is normally focussed on fuel production via ethanol or heat. In this work, a techno-economic assessment of a biorefinery with three product streams, cellulose, hemicellulose and lignin is presented. Moreover, the techno-economic assessment is evaluated in the context of the supply chain through optimisation. A mixed integer linear program was developed to allow for flexible scenarios in order to determine effects of technological and pre-processing variations on the supply chain. The techno-economic and optimisation model integration was demonstrated on a case study in Scotland using woody biomass, either as sawnlogs or sawmill chips. It was established that sawmill chips is the preferred option, however sawnlogs became competitive once passive drying to 30% moisture content (wet basis) was considered. The flexibility of the modelling approach allowed for consideration of technology savings in the context of the supply chain, which can impact development choices.

A process for producing lignin and volatile compounds from hydrolysis liquor

BACKGROUND

Hot water hydrolysis process is commercially applied for treating wood chips prior to pulping or wood pellet production, while it produces hydrolysis liquor as a by-product. Since the hydrolysis liquor is dilute, the production of value-added materials from it would be challenging.

RESULTS

In this study, acidification was proposed as a viable method to extract (1) furfural and acetic acid from hot water hydrolysis liquor and (2) lignin compounds from the liquor. The thermal properties of the precipitates made from the acidification of hydrolysis liquor confirmed the volatile characteristics of precipitates. Membrane dialysis was effective in removing inorganic salts associated with lignin compounds. The purified lignin compounds had a glass transition temperature (Tg) of 180-190 °C, and were thermally stable.

CONCLUSIONS

The results confirmed that lignin compounds present in hot water hydrolysis liquor had different characteristics. The acidification of hydrolysis liquor primarily removed the volatile compounds from hydrolysis liquor. Based on these results, a process for producing purified lignin and precipitates of volatile compounds was proposed.

Novel rapid method for the characterisation of polymeric sugars from macroalgae

Laminarins are storage polysaccharides found only in brown seaweeds, specifically Laminarialaes and Fucales. Laminarin has been shown to have anti-apoptotic and anti-tumoural activities and is considered as a nutraceutical component that can positively influence human health. The structure is species dependent, generally composed of linear ß(1-3) glucans with intrachain β(1-6) branching and varies according to harvest season and environmental factors. Current methods for analysis of molar mass and DP length are technically demanding and are not widely available. Here, we present a simple inexpensive method which enables rapid analysis of laminarins from macroalgal biomass using high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) without the need for hydrolysis or further processing. This is based on the linear relationship observed between log₁₀ DP and retention time following separation of laminarins on a CarboPac PA-100 column (Dionex) using standard 1,3-β-d-gluco-oligosaccharides ranging in DP from 2 to 8. This method was applied to analyse laminarin oligomers in extracts from different species harvested from within the intertidal zone on Welsh rocky shores containing laminarin polymers with different ranges of DP. The degree of polymerisation and extrapolated molar mass agreed well with values estimated by LC-ESI/MS ⁿ analysis and those reported in the literature.

Enzymatic saccharification of brown seaweed for production of fermentable sugars

This study shows that high drying temperatures negatively affect the enzymatic saccharification yield of the brown seaweed Saccharina latissima. The optimal drying temperature of the seaweed in terms of enzymatic sugar release was found to be 30°C. The enzymatic saccharification process was optimized by investigating factors such as kinetics of sugar release, enzyme dose, solid loading and different blend ratios of cellulases and an alginate lyase. It was found that the seaweed biomass could be efficiently hydrolysed to fermentable sugars using a commercial cellulase cocktail. The inclusion of a mono-component alginate lyase was shown to improve the performance of the enzyme blend, in particular at high solid loadings. At 25% dry matter loading a combined glucose and mannitol concentration of 74g/L was achieved.

Saccharification of newspaper waste after ammonia fiber expansion or extractive ammonia

The lignocellulosic fractions of municipal solid waste (MSW) can be used as renewable resources due to the widespread availability, predictable and low pricing and suitability for most conversion technologies. In particular, after the typical paper recycling loop, the newspaper waste (NW) could be further valorized as feedstock in biorefinering industry since it still contains up to 70 % polysaccharides. In this study, two different physicochemical methods-ammonia fiber expansion (AFEX) and extractive ammonia (EA) were tested for the pretraetment of NW. Furthermore, based on the previously demonstrated ability of the recombinant enzymes endocellulase rCelStrep, α-L-arabinofuranosidase rPoAbf and its evolved variant rPoAbf F435Y/Y446F to improve the saccharification of different lignocellulosic pretreated biomasses (such as corn stover and Arundo donax), in this study these enzymes were tested for the hydrolysis of pretreated NW, with the aim of valorizing the lignocellulosic fractions of the MSW. In particular, a mixture of purified enzymes containing cellulases, xylanases and accessory hemicellulases, was chosen as reference mix and rCelStrep and rPoAbf or its variant were replaced to EGI and Larb. The results showed that these enzymatic mixes are not suitable for the hydrolysis of NW after AFEX or EA pretreatment. On the other hand, when the enzymes rCelStrep, rPoAbf and rPoAbf F435Y/Y446F were tested for their effect in hydrolysis of pretreated NW by addition to a commercial enzyme mixture, it was shown that the total polysaccharides conversion yield reached 37.32 % for AFEX pretreated NW by adding rPoAbf to the mix whilst the maximum sugars conversion yield for EA pretreated NW was achieved 40.80 % by adding rCelStrep. The maximum glucan conversion yield obtained (45.61 % for EA pretreated NW by adding rCelStrep to the commercial mix) is higher than or comparable to those reported in recent manuscripts adopting hydrolysis conditions similar to those used in this study.

Pretreatment of lignocellulose: Formation of inhibitory by-products and strategies for minimizing their effects

Biochemical conversion of lignocellulosic feedstocks to advanced biofuels and other commodities through a sugar-platform process involves a pretreatment step enhancing the susceptibility of the cellulose to enzymatic hydrolysis. A side effect of pretreatment is formation of lignocellulose-derived by-products that inhibit microbial and enzymatic biocatalysts. This review provides an overview of the formation of inhibitory by-products from lignocellulosic feedstocks as a consequence of using different pretreatment methods and feedstocks as well as an overview of different strategies used to alleviate problems with inhibitors. As technologies for biorefining of lignocellulose become mature and are transferred from laboratory environments to industrial contexts, the importance of management of inhibition problems is envisaged to increase as issues that become increasingly relevant will include the possibility to use recalcitrant feedstocks, obtaining high product yields and high productivity, minimizing the charges of enzymes and microorganisms, and using high solids loadings to obtain high product titers.

Optimization-based methodology for the development of wastewater facilities for energy and nutrient recovery

A paradigm shift is currently underway from an attitude that considers wastewater streams as a waste to be treated, to a proactive interest in recovering materials and energy from these streams. This paper is concerned with the development and application of a systematic, model-based methodology for the development of wastewater resource recovery systems that are both economically attractive and sustainable. With the array of available treatment and recovery options growing steadily, a superstructure modeling approach based on rigorous mathematical optimization appears to be a natural approach for tackling these problems. The development of reliable, yet simple, performance and cost models is a key issue with this approach in order to allow for a reliable solution based on global optimization. We argue that commercial wastewater simulators can be used to derive such models, and we illustrate this approach with a simple resource recovery system. The results show that the proposed methodology is computationally tractable, thereby supporting its application as a decision support system for selection of promising resource recovery systems whose development is worth pursuing.

The bio refinery; producing feed and fuel from grain

It is both possible and practicable to produce feed and fuel from grain. Using the value of grain to produce renewable energy for transport, while using the remaining protein content of the grain as a valuable protein source for livestock and for fish, can be seen as a complimentary and optimal use of all the grain constituents. Consideration must be given to maximise the value of the yeast components, as substantial yeast is generated during the fermentation of the grain starch to produce ethanol. Yeast is a nutritionally rich feed ingredient, with potential for use both as feed protein and as a feed supplement with possible immunity and gut health enhancing properties. Bioprocessing, with the consequent economies of scale, is a process whereby the value of grain can be optimised in a way that is traditional, natural and sustainable for primarily producing protein and oil for feed with a co-product ethanol as a renewable fuel.

Use of a mannitol rich ensiled grass press juice (EGPJ) as a sole carbon source for polyhydroxyalkanoates (PHAs) production through high cell density cultivation

This study demonstrates the use of a mannitol rich ensiled grass press juice (EGPJ) as a renewable carbon substrate for polyhydroxyalkanoates (PHA) production in shaking flask experiments and fed-batch stirred tank reactor cultivations. Fed-batch cultivations of Burkholderia sacchari IPT101 using EGPJ as sole carbon source produced 44.5 g/L CDW containing 33% polyhydroxybutyrate (PHB) in 36 h, while Pseudomonas chlororaphis IMD555 produced a CDW of 37 g/L containing 10% of medium chain length polyhydroxyalkanoates (mcl-PHA) in 34 h. PHB and mcl-PHA extracted from B. sacchari IPT101 and P. chlororaphis IMD555, grown on EGPJ, had a molecular weight of 548 kg/mol and 115.4 kg/mol, respectively. While mcl-PHA can be produced from EGPJ, PHB production is more interesting as there is a 4-fold higher volumetric productivity compared to mcl-PHA.

High-level expression, purification and characterization of carbazole dioxygenase, a three components dioxygenase, of Pseudomonas GBS.5

OBJECTIVE

To investigate the conversion of carbazole into 2'-aminobiphenyl-2,3-diol using carbazole dioxygenase (CARDO) that is a multicomponent enzyme consisting of homotrimeric terminal oxygenases (CarAa), a ferredoxin (CarAc) and a ferredoxin reductase (CarAd) unit, encoded by the carAa, carAc and carAd genes, respectively.

RESULTS

The enzyme subunits containing a GST tag were expressed independently in E. coli. The expressed proteins were purified by one-step immobilized affinity chromatography and three purified proteins could reconstitute the CARDO activity in vitro and showed activity against carbazole as well as against wide range of polyaromatic compounds.

CONCLUSION

This method provides an efficient way to obtain an active carbazole dioxygenase with high yield, high purity and with activity against a wide range of polyaromatic compounds.

Indole generates quiescent and metabolically active Escherichia coli cultures

An inherent problem with bacterial cell factories used to produce recombinant proteins or metabolites is that resources are channeled into unwanted biomass as well as product. Over several years, attempts have been made to increase efficiency by unlinking biomass and product generation. One example was the quiescent cell (Q-Cell) expression system that generated non-growing but metabolically active Escherichia coli by over-expressing a regulatory RNA (Rcd) in a defined genetic background. Although effective at increasing the efficiency with which resources are converted to product, the technical complexity of the Rcd-based Q-Cell system limited its use. We describe here an alternative method for generating Q-Cells by the direct addition of indole, or related indole derivatives, to the culture medium of an E. coli strain carrying defined mutations in the hns gene. This simple and effective approach is shown to be functional in both shake-flask and fermenter culture. The cells remain metabolically active and analysis of their performance in the fermenter suggests that they may be particularly suitable for the production of cellular metabolites.

Methodology for enabling high-throughput simultaneous saccharification and fermentation screening of yeast using solid biomass as a substrate

BACKGROUND

High-throughput (HTP) screening is becoming an increasingly useful tool for collating biological data which would otherwise require the employment of excessive resources. Second generation biofuel production is one such process. HTP screening allows the investigation of large sample sets to be undertaken with increased speed and cost effectiveness. This paper outlines a methodology that will enable solid lignocellulosic substrates to be hydrolyzed and fermented at a 96-well plate scale, facilitating HTP screening of ethanol production, whilst maintaining repeatability similar to that achieved at a larger scale.

RESULTS

The results showed that utilizing sheets of biomass of consistent density (handbills), for paper, and slurries of pretreated biomass that could be pipetted allowed standardized and accurate transfers to 96-well plates to be achieved (±3.1 and 1.7%, respectively). Processing these substrates by simultaneous saccharification and fermentation (SSF) at various volumes showed no significant difference on final ethanol yields, either at standard shake flask (200 mL), universal bottle (10 mL) or 96-well plate (1 mL) scales. Substrate concentrations of up to 10% (w/v) were trialed successfully for SSFs at 1 mL volume. The methodology was successfully tested by showing the effects of steam explosion pretreatment on both oilseed rape and wheat straws.

CONCLUSIONS

This methodology could be used to replace large shake flask reactions with comparatively fast 96-well plate SSF assays allowing for HTP experimentation. Additionally this method is compatible with a number of standardized assay techniques such as simple colorimetric, High-performance liquid chromatography (HPLC) and Nuclear magnetic resonance (NMR) spectroscopy. Furthermore this research has practical uses in the biorefining of biomass substrates for second generation biofuels and novel biobased chemicals by allowing HTP SSF screening, which should allow selected samples to be scaled up or studied in more detail.

Robust enzymatic hydrolysis of Formiline-pretreated oil palm empty fruit bunches (EFB) for efficient conversion of polysaccharide to sugars and ethanol

Oil palm empty fruit bunch (EFB) was pretreated by Formiline process to overcome biomass recalcitrance and obtain hemicellulosic syrup and lignin. Higher formic acid concentration led to more lignin removal but also higher degree of cellulose formylation. Cellulose digestibility could be well recovered after deformylation with a small amount of lime. After digested by enzyme loading of 15 FPU+10 CBU/g solid for 48 h, the polysaccharide conversion could be over 90%. Simultaneous saccharification and fermentation (SSF) results demonstrated that ethanol concentration reached 83.6 g/L with approximate 85% of theoretic yield when performed at an initial dry solid consistency of 20%. A mass balance showed that via Formiline pretreatment 0.166 kg of ethanol could be produced from 1 kg of dry EFB with co-production of 0.14 kg of high-purity lignin and 5.26 kg hemicellulosic syrup containing 2.8% xylose. Formiline pretreatment thus can be employed as an entry for biorefining of EFB.

Efficient conversion of brown grease produced by municipal wastewater treatment plant into biofuel using aluminium chloride hexahydrate under very mild conditions

Wastes produced by oil/water separation at the wastewater treatment plant of Bari West (Southern Italy) were taken, characterized and converted. About 12% of this material was composed of greases, mainly made of free fatty acids (50%) and soaps (34%), and was easily separable by the aqueous phase through a hot centrifugation. After chemical activation of this fatty fraction, a direct esterification was carried out under very mild conditions (320K and atmospheric pressure), converting more than 90% of the original free fatty acids into the respective methyl esters in less than 4h, by using AlCl3·6H2O. The activation energy correlated to the use of this catalyst was also calculated (Eaest=43.9kJmol(-1)). The very low cost of the biodiesel produced (0.45€L(-1)) and the associated relevant specific energy (5.02MJ kgFAMEs(-1)) make such a process a really sustainable and effective example of valorization of a waste.

Synergistic benefits of ionic liquid and alkaline pretreatments of poplar wood. Part 1: effect of integrated pretreatment on enzymatic hydrolysis

An environmentally friendly pretreatment process was developed to fractionate hemicelluloses and lignin from poplar wood by ionic liquid (IL) pretreatment coupled with mild alkaline extraction. Hemicellulosic and lignin fractions were obtained in high yields, amounting to 59.3% and 74.4%, respectively, which can served as raw materials for production of value-added products. The yield of glucose for the integrated pretreated poplar wood was 99.2%, while it was just 19.2% for the untreated material. The synergistic benefits of the removal of lignin and hemicelluloses, the increase of the cellulose surface area, and the conversion of cellulose fibers from the cellulose I to the cellulose II crystal phase resulted in the high glucose yield for the integrated pretreated substrate. Therefore, the IL based biorefining strategy proposed can integrate biofuels production into a biorefinery scheme in which the major components of poplar wood can be converted into value-added products.