Fumaric Acid Production: A Biorefinery Perspective

An effective visible-light driven fumarate production from gaseous CO2 and pyruvate by the cationic zinc porphyrin-based photocatalytic system with dual biocatalysts

Fumaric acid is a useful unsaturated dicarboxylic acid that serves as a precursor for the biodegradable plastics poly(butylene succinate) and poly(propylene fumarate). Currently, fumaric acid is mainly synthesised from petroleum resources such as benzene. It is therefore desirable to develop methods to produce fumaric acid from renewable resources such as those derived from biomass. In this work, an effective visible-light driven fumarate production from gaseous CO2 and pyruvate with the system consisting of triethanolamine, cationic water-soluble zinc porphyrin, zinc tetrakis(4-N,N,N-trimethylaminophenyl)porphyrin, pentamethylcyclopentadienyl coordinated rhodium(III) 2,2'-bipyridyl complex, NAD+, malate dehydrogenase (NAD+-dependent oxaloacetate-decarboxylating) and fumarase was developed.

Metabolic engineering and fermentation optimization strategies for producing organic acids of the tricarboxylic acid cycle by microbial cell factories

The organic acids of the tricarboxylic acid (TCA) pathway are important platform compounds and are widely used in many areas. The high-productivity strains and high-efficient and low-cost fermentation are required to satisfy a huge market size. The high metabolic flux of the TCA pathway endows microorganisms potential to produce high titers of these organic acids. Coupled with metabolic engineering and fermentation optimization, the titer of the organic acids has been significantly improved in recent years. Herein, we discuss and compare the recent advances in synthetic pathway engineering, cofactor engineering, transporter engineering, and fermentation optimization strategies to maximize the biosynthesis of organic acids. Such engineering strategies were mainly based on the TCA pathway and glyoxylate pathway. Furthermore, organic-acid-secretion enhancement and renewable-substrate-based fermentation are often performed to assist the biosynthesis of organic acids. Further strategies are also discussed to construct high-productivity and acid-resistant strains for industrial large-scale production.

Recent advances and perspectives on production of value-added organic acids through metabolic engineering

Organic acids are important consumable materials with a wide range of applications in the food, biopolymer and chemical industries. The global consumer organic acids market is estimated to increase to $36.86 billion by 2026. Conventionally, organic acids are produced from the chemical catalysis process with petrochemicals as raw materials, which posts severe environmental concerns and conflicts with our sustainable development goals. Most of the commonly used organic acids can be produced from various organisms. As a state-of-the-art technology, large-scale fermentative production of important organic acids with genetically-modified microbes has become an alternative to the chemical route to meet the market demand. Despite the fact that bio-based organic acid production from renewable cheap feedstock provides a viable solution, low productivity has impeded their industrial-scale application. With our deeper understanding of strain genetics, physiology and the availability of strain engineering tools, new technologies including synthetic biology, various metabolic engineering strategies, omics-based system biology tools, and high throughput screening methods are gradually established to bridge our knowledge gap. And they were further applied to modify the cellular reaction networks of potential microbial hosts and improve the strain performance, which facilitated the commercialization of consumable organic acids. Here we present the recent advances of metabolic engineering strategies to improve the production of important organic acids including fumaric acid, citric acid, itaconic acid, adipic acid, muconic acid, and we also discuss the current challenges and future perspectives on how we can develop a cost-efficient, green and sustainable process to produce these important chemicals from low-cost feedstocks.

Fumaric Acid Production by R. arrhizus NRRL 1526 Using Apple Pomace Enzymatic Hydrolysates: Kinetic Modelling

Fumaric acid is one of the most promising biorefinery platform chemicals, fruit residues being a very suitable raw material for its production in second generation biorefineries. In particular, apple pomace is a plentiful residue from the apple juice industry, with apple being the second largest fruit crop in the world, with a production that increased from 46 to 86 Mtons in the 1994–2021 period. With a global apple juice production of more than 4.5 Mtons, a similar amount of apple pomace is produced yearly. In this work, apple pomace hydrolysate has been obtained by enzymatic hydrolysis and further characterized for its content in sugars, phenolics and nitrogen using different analytic methods, based on HPLC and colorimetric techniques. Previous to the use of this hydrolysate (APH), we studied if the addition of fructose to the usual glucose-rich broth could lead to high fumaric acid yields, titers and productivities. Afterwards, APH fermentation was performed and improved using different nitrogen initial amounts, obtaining production yields (0.32 gFumaric acid/gconsumed sugar) similar to those obtained with synthetic media (0.38 gFumaric acid/gconsumed sugar). Kinetic modelling was employed to evaluate, explain, and understand the experimental values and trends of relevant components in the fermentation broth as functions of the bioprocess time, proposing a suitable reaction scheme and a non-structured, non-segregated kinetic model based on it.

Fumaric acid: fermentative production, applications and future perspectives

The rising prices of petroleum-based chemicals and the growing apprehension about food safety and dairy supplements have reignited interest in fermentation process to produce fumaric acid. This article reviews the main issues associated with industrial production of fumaric acid. Different approaches such as strain modulation, morphological control, selection of substrate and fermentative separation have been addressed and discussed followed by their potential towards production of fumaric acid at industrial scale is highlighted. The employment of biodegradable wastes as substrates for the microorganisms involved in fumaric acid synthesis has opened an economic and green route for production of the later on a commercial scale. Additionally, the commercial potential and technological approaches to the augmented fumaric acid derivatives have been discussed. Conclusion of the current review reveals future possibilities for microbial fumaric acid synthesis.

Photocatalyzed Functionalization of Alkenoic Acids in 3D-Printed Reactors

The valorization of alkenoic acids possibly deriving from biomass (fumaric and citraconic acids) was carried out through conversion in important building blocks, such as γ-keto acids and succinic acid derivatives. The functionalization was carried out by addition onto the C=C double bond of radicals generated under photocatalyzed conditions from suitable hydrogen donors (mainly aldehydes) and by adopting a decatungstate salt as the photocatalyst. Syntheses were performed under batch (in a glass vessel) and flow (by using 3D-printed reactors) conditions. The design of the latter reactors allowed for an improved yield and productivity.

Rhizopus oryzae for Fumaric Acid Production: Optimising the Use of a Synthetic Lignocellulosic Hydrolysate

The hydrolysis of lignocellulosic biomass opens an array of bioconversion possibilities for producing fuels and chemicals. Microbial fermentation is particularly suited to the conversion of sugar-rich hydrolysates into biochemicals. Rhizopus oryzae ATCC 20344 was employed to produce fumaric acid from glucose, xylose, and a synthetic lignocellulosic hydrolysate (glucose–xylose mixture) in batch and continuous fermentations. A novel immobilised biomass reactor was used to investigate the co-fermentation of xylose and glucose. Ideal medium conditions and a substrate feed strategy were then employed to optimise the production of fumaric acid. The batch fermentation of the synthetic hydrolysate at optimal conditions (urea feed rate 0.625mgL−1h−1 and pH 4) produced a fumaric acid yield of 0.439gg−1. A specific substrate feed rate (0.164gL−1h−1) that negated ethanol production and selected for fumaric acid was determined. Using this feed rate in a continuous fermentation, a fumaric acid yield of 0.735gg−1 was achieved; this was a 67.4% improvement. A metabolic analysis helped to determine a continuous synthetic lignocellulosic hydrolysate feed rate that selected for fumaric acid production while achieving the co-fermentation of glucose and xylose, thus avoiding the undesirable carbon catabolite repression. This work demonstrates the viability of fumaric acid production from lignocellulosic hydrolysate; the process developments discovered will pave the way for an industrially viable process.

A Review on the Production of C4 Platform Chemicals from Biochemical Conversion of Sugar Crop Processing Products and By-Products

The development and commercialization of sustainable chemicals from agricultural products and by-products is necessary for a circular economy built on renewable natural resources. Among the largest contributors to the final cost of a biomass conversion product is the cost of the initial biomass feedstock, representing a significant challenge in effective biomass utilization. Another major challenge is in identifying the correct products for development, which must be able to satisfy the need for both low-cost, drop-in fossil fuel replacements and novel, high-value fine chemicals (and/or commodity chemicals). Both challenges can be met by utilizing wastes or by-products from biomass processing, which have very limited starting cost, to yield platform chemicals. Specifically, sugar crop processing (e.g., sugarcane, sugar beet) is a mature industry that produces high volumes of by-products with significant potential for valorization. This review focuses specifically on the production of acetoin (3-hydroxybutanone), 2,3-butanediol, and C4 dicarboxylic (succinic, malic, and fumaric) acids with emphasis on biochemical conversion and targeted upgrading of sugar crop products/by-products. These C4 compounds are easily derived from fermentations and can be converted into many different final products, including food, fragrance, and cosmetic additives, as well as sustainable biofuels and other chemicals. State-of-the-art literature pertaining to optimization strategies for microbial conversion of sugar crop byproducts to C4 chemicals (e.g., bagasse, molasses) is reviewed, along with potential routes for upgrading and valorization. Directions and opportunities for future research and industrial biotechnology development are discussed.

Modelling and Environmental Profile Associated with the Valorization of Wheat Straw as Carbon Source in the Biotechnological Production of Manganese Peroxidase

Interest in the development of biorefineries and biotechnological processes based on renewable resources has multiplied in recent years. This driving force is the result of the availability of lignocellulosic biomass and the range of applications that arise from its use and valorization. The approach of second-generation sugars from lignocellulosic biomass opens up the possibility of producing biotechnological products such as enzymes as a feasible alternative in the framework of biorefineries. It is in this context that this manuscript is framed, focusing on the modelling of a large-scale fermentative biotechnological process to produce the enzyme manganese peroxidase (MnP) by the fungus Irpex lacteus using wheat straw as a carbon source. The production scheme is based on the sequence of four stages: pretreatment of wheat straw, seed fermenters, enzyme production and downstream processes. For its environmental assessment, the Life Cycle Assessment methodology, which allows the identification and quantification of environmental impacts associated with the process, was utilized. As the main finding, the stages of the process with the highest environmental burdens are those of pretreatment and fermentation, mainly due to energy requirements. With the aim of proposing improvement scenarios, sensitivity analyses were developed around the identified hotspots. An improvement in the efficiency of steam consumption leads to a reduction of environmental damage of up to 30%.

Engineering Escherichia coli for efficient aerobic conversion of glucose to fumaric acid

Escherichia coli was engineered for efficient aerobic conversion of glucose to fumaric acid. A novel design for biosynthesis of the target product through the modified TCA cycle rather than via glyoxylate shunt, implying oxaloacetate formation from pyruvate and artificial channelling of 2-ketoglutarate towards succinic acid via succinate semialdehyde formation, was implemented. The main fumarases were inactivated in the core strain MSG1.0 (∆ackA-pta, ∆poxB, ∆ldhA, ∆adhE, ∆ptsG, PL-glk, Ptac-galP) by the deletion of the fumA, fumB, and fumC genes. The Bacillus subtilis pycA gene was expressed in the strain to ensure pyruvate to oxaloacetate conversion. The Mycobacterium tuberculosis kgd gene was expressed to enable succinate semialdehyde formation. The resulting strain was able to convert glucose to fumaric acid with a yield of 0.86 mol/mol, amounting to 86% of the theoretical maximum. The results demonstrated the high potential of the implemented strategy for development of efficient strains for bio-based fumaric acid production.

Production of Fumaric Acid by Rhizopus arrhizus NRRL 1526: A Simple Production Medium and the Kinetic Modelling of the Bioprocess

Fumaric acid is a promising monomer to obtain biomass-based polyesters and polyamides, and it is mainly produced by fungi of the Rhizopus genus in medium to high titters. The use of glucose, a main component of starchy and cellulosic food waste, as carbon source, together with a low-nitrogen source concentration, is a promising route to reduce process costs. In this work, the effects of nitrogen and carbonate sources on Rhizopus arrhizus NRRL 1526 morphology and fumaric acid productivity were analysed, simplifying the traditional production broth composition. Moreover, a non-structured, non-segregated kinetic model was proposed and fitted to concentration data of all relevant components obtained in batches performed in triplicate with the selected production broth at 34 °C and 200 rpm in an orbital shaker.

A Novel Multilayer Natural Coating for Fed-State Gastric Protection

Several nutraceutical products require gastric protection against the hostile environment in the stomach. Currently marketed synthetic and semi-synthetic coatings suffer from major shortcomings such as poor gastric protection, slow-release response to pH change, and the use of artificial ingredients. The challenge of coating natural products is further exacerbated by the relatively high gastric pH in the fed state. In this work, a novel natural enteric coating is presented as a breakthrough alternative to current solutions. Two coating systems were devised: (i) a triple-layer coating that comprises a wax layer embedded between two alginate-based coatings, and (ii) a double-layer coating, where an overcoat of organic acids (fumaric or citric acid) is applied to an alginate-based coating. The multi-layer architecture did not impact the pH-responsive nature of the coating even when more biologically relevant Krebs bicarbonate buffer of lower buffer capacity was used. Interestingly, the gastric protection barrier of organic acid-based coating remained resistant at elevated gastric pH 2, 3, or 4 for 2 h. This is the first report of using an alginate-based coating to provide gastric protection against fed-state stomach conditions (pH 2–4). Being biodegradable, naturally occurring, and with no limit on daily intake, the reported novel coating provides a superior platform to current coating solutions for pharmaceutical and nutraceutical products.

Continuous Production of Fumaric Acid with Immobilised Rhizopus oryzae: The Role of pH and Urea Addition

Fumaric acid is widely used in the food and beverage, pharmaceutical and polyester resin industries. Rhizopus oryzae is the most successful microorganism at excreting fumaric acid compared to all known natural and genetically modified organisms. It has previously been discovered that careful control of the glucose feed rate can eliminate the by-product formation of ethanol. Two key parameters affecting fumaric acid excretion were identified, namely the medium pH and the urea feed rate. A continuous fermentation with immobilised R. oryzae was utilised to determine the effect of these parameters. It was found that the selectivity for fumaric acid production increased at high glucose consumption rates for a pH of 4, different from the trend for pH 5 and 6, achieving a yield of 0.93 gg−1. This yield is higher than previously reported in the literature. Varying the urea feed rate to 0.255 mgL−1h−1 improved the yield of fumaric acid but experienced a lower glucose uptake rate compared to higher urea feed rates. An optimum region has been found for fumaric acid production at pH 4, a urea feed rate of 0.625 mgL−1h−1 and a glucose feed rate of 0.329 gL−1h−1.

Host Stress Signals Stimulate Pneumococcal Transition from Colonization to Dissemination into the Lungs

Streptococcus pneumoniae is an asymptomatic colonizer of the nasopharynx, but it is also one of the most important bacterial pathogens of humans, causing a wide range of mild to life-threatening diseases. The basis of the pneumococcal transition from a commensal to a parasitic lifestyle is not fully understood. We hypothesize that exposure to host catecholamine stress hormones is important for this transition. In this study, we demonstrated that pneumococci preexposed to a hormone released during stress, norepinephrine (NE), have an increased capacity to translocate from the nasopharynx into the lungs compared to untreated pneumococci. Examination of NE-treated pneumococci revealed major alterations in metabolic profiles, cell associations, capsule synthesis, and cell size. By systemically mutating all 12 two-component and 1 orphan regulatory systems, we also identified a unique genetic regulatory circuit involved in pneumococcal recognition and responsiveness to human stress hormones. IMPORTANCE Microbes acquire unique lifestyles under different environmental conditions. Although this is a widespread occurrence, our knowledge of the importance of various host signals and their impact on microbial behavior is not clear despite the therapeutic value of this knowledge. We discovered that catecholamine stress hormones are the host signals that trigger the passage of Streptococcus pneumoniae from a commensal to a parasitic state. We identify that stress hormone treatment of this microbe leads to reductions in cell size and capsule synthesis and renders it more able to migrate from the nasopharynx into the lungs in a mouse model of infection. The microbe requires the TCS09 protein for the recognition and processing of stress hormone signals. Our work has particular clinical significance as catecholamines are abundant in upper respiratory fluids as well as being administered therapeutically to reduce inflammation in ventilated patients, which may explain why intubation in the critically ill is a recognized risk factor for the development of pneumococcal pneumonia.

Fumaric acid production using alternate fermentation mode by immobilized Rhizopus oryzae-a greener production strategy

The current work investigates the impact of using immobilized Rhizopus oryzae NRRL 1526 for bioproduction of fumaric acid using agro-industrial residues as feedstock. This use of agro-industrial residues, a renewable feedstock, for the production of bio-based platform chemical makes the process cost-competitive as well as greener by preventing the release of assimilable organic carbon to the environment, thereby reducing the generation of greenhouse gases. Immobilization of R. oryzae has been proposed previously to alleviate operational difficulties confronted during free mycelial fungal fermentation. To this effect, three synthetic refuse materials namely polystyrene foam, polyester sponge and polyurethane foam were investigated for their suitability towards fumaric acid bioproduction. Polystyrene foam was identified as the most suitable support material for immobilization as well as fumaric acid production. In addition to the considerable reduction in the lag-phase (from 48 to 24 h) the reduction in the size of the support material from cubes of 1 cm to beads of 0.1-0.3 cm led to a 42% improvement in fumaric acid production (27 g/L against 19 g/L). Growing the polystyrene foam bead immobilized R. oryzae on apple pomace ultrafiltration sludge as sole feedstock yielded a final fumaric acid titer of 7.9 g/L whereas free mycelial fermentation yielded 6.3 g/L. Moreover, upon operating the fermentation with intermittent feeding, a three-fold increase (1.7 g/L to 5.1 g/L) in fumaric acid production was obtained upon supplementation of the apple pomace sludge media with molasses, an agro-industrial residue, as feed.

Restricted Nitrogen and Water Applications in the Orchard Modify the Carbohydrate and Amino Acid Composition of Nonpareil and Carmel Almond Hulls

Hull rot disease of almond (Prunus dulcis), caused by the fungus Rhizopus stolonifer, is prevalent in well maintained orchards where trees are provided plenty of water and nitrogen to increase the growth and yield. The predominantly grown variety Nonpareil is considered very susceptible to hull rot, while the pollinator variety Carmel is more resistant. Reduced nitrogen rates and restricted irrigation scheduling decreased the incidence and severity of hull rot in Californian orchards. As a part of our research, the hull composition of Australian almond fruits of Nonpareil and Carmel varieties, grown under two levels of irrigation (high and low) and two levels of nitrogen (high and low), were analysed using ¹H NMR-based metabolomics. Both Nonpareil and Carmel hulls contained sugars such as glucose, sucrose, fructose and xylose, and amino acids, particularly asparagine. Variety was the major factor with Nonpareil hulls significantly higher in sugars and asparagine than Carmel. Within varieties, nitrogen influenced the relative concentrations of glucose, sucrose and asparagine. In Nonpareil, high nitrogen high water (the control) had relatively high glucose and asparagine content. High nitrogen low water increased the sucrose component, low nitrogen high water increased the glucose component and low nitrogen low water increased the sucrose and asparagine components. In Carmel, however, high nitrogen low water and low nitrogen high water increased sucrose and asparagine, and low nitrogen low water increased sucrose and glucose. Hull rot symptoms are caused by fumaric acid production by R. stolonifer growing within the hull. These changes in the hull composition under different nitrogen and water scenarios have the potential to affect the growth of R. stolonifer and its metabolite production in hull rot disease.

Added-Value Chemicals from Lignin Oxidation

Lignin is the second most abundant component, next to cellulose, in lignocellulosic biomass. Large amounts of this polymer are produced annually in the pulp and paper industries as a coproduct from the cooking process-most of it burned as fuel for energy. Strategies regarding lignin valorization have attracted significant attention over the recent decades due to lignin's aromatic structure. Oxidative depolymerization allows converting lignin into added-value compounds, as phenolic monomers and/or dicarboxylic acids, which could be an excellent alternative to aromatic petrochemicals. However, the major challenge is to enhance the reactivity and selectivity of the lignin structure towards depolymerization and prevent condensation reactions. This review includes a comprehensive overview of the main contributions of lignin valorization through oxidative depolymerization to produce added-value compounds (vanillin and syringaldehyde) that have been developed over the recent decades in the LSRE group. An evaluation of the valuable products obtained from oxidation in an alkaline medium with oxygen of lignins and liquors from different sources and delignification processes is also provided. A review of C4 dicarboxylic acids obtained from lignin oxidation is also included, emphasizing catalytic conversion by O2 or H2O2 oxidation.

Evaluation of biomass pretreatment to optimize process factors for different organic acids via Box-Behnken RSM method

Biomass, as renewable energy source, is of importance to investigate to extend the conversion yield by microorganism. Because of lignocellulosic structure, biomass must be pretreated with a process, frequently inorganic acid has to be used with a problem of hazardous byproducts. Organic acid pretreatment is an efficient alternative to be investigated. Sugar beet pulp, as an agro-industrial residue of microorganism, can be utilized by pretreatment, which is usually a costly process. Pretreatment with organic acids creates a great opportunity to convert the process into more economic and effective. Moreover, pressure conditions significantly increase the yield of biodegradable sugar content. In this study, different organic acids of maleic, fumaric, oxalic, and acetic acid pretreatment was investigated to pretreatment of sugar beet pulp, which came vast amount from factories, under pressure and non-pressure conditions via Box-Behnken method to estimate optimum point of acid ratio (1, 3, 5%), time (10, 27.5, 45 min), and solid ratio factors (3, 6.5, 10%) for highest degradation. Results were also evaluated economically. As a result of the experiments, it was observed that acetic acid gave the best result with 409.16 g/L total sugar concentration than the other organic acids. The highest TS concentration of maleic, oxalic, and fumaric acid were 97.26, 97.85, and 91.37 g/L, respectively, under pressure. According to economical evaluation, owing to lower market price and highest TS formation yield, pretreatment cost of acetic acid pretreatment was found averagely 1.51 $/gTS under pressure conditions.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10163-021-01276-7.

Capability Enhancement of Fumaric Acid Production by Rhizopus arrhizus Through Carbon-Nitrogen Sources Coordination

Fumaric acid production from the fermentation process by Rhizopus was considered a potential method. But poor conversion efficiency and low space-time productivity greatly hampered industrial production. Here, we reported improving these problems through carbon-nitrogen sources coordination optimization strategy. Five commonly used nitrogen sources were selected to conduct element analysis and fermentation efficiency comparison. Casein was proven to be the optimum nitrogen source and further investigated in a stirred-tank reactor. It showed that the fermentation cycle was significantly shortened by the application of casein. Combined with optimization of glucose content, the space-time productivity of fumaric acid reached 0.76 g/L h with a yield to 0.31 g/g glucose, which was the highest among the results gotten in the stirred-tank reactor. It illustrated that carbon-nitrogen sources coordination optimization strategy was in favor of the improvement of the fermentation process and laid a promising foundation for the development of fumaric acid industrial production.

Reaction of H2 with mitochondria-relevant metabolites using a multifunctional molecular catalyst

The Krebs cycle is the fuel/energy source for cellular activity and therefore of paramount importance for oxygen-based life. The cycle occurs in the mitochondrial matrix, where it produces and transfers electrons to generate energy-rich NADH and FADH₂, as well as C₄-, C₅-, and C₆-polycarboxylic acids as energy-poor metabolites. These metabolites are biorenewable resources that represent potential sustainable carbon feedstocks, provided that carbon-hydrogen bonds are restored to these molecules. In the present study, these polycarboxylic acids and other mitochondria-relevant metabolites underwent dehydration (alcohol-to-olefin and/or dehydrative cyclization) and reduction (hydrogenation and hydrogenolysis) to diols or triols upon reaction with H₂, catalyzed by sterically confined iridium-bipyridyl complexes. The investigation of these single-metal site catalysts provides valuable molecular insights into the development of molecular technologies for the reduction and dehydration of highly functionalized carbon resources.

Continuous Flow Upgrading of Selected C2-C6 Platform Chemicals Derived from Biomass

The ever increasing industrial production of commodity and specialty chemicals inexorably depletes the finite primary fossil resources available on Earth. The forecast of population growth over the next 3 decades is a very strong incentive for the identification of alternative primary resources other than petro-based ones. In contrast with fossil resources, renewable biomass is a virtually inexhaustible reservoir of chemical building blocks. Shifting the current industrial paradigm from almost exclusively petro-based resources to alternative bio-based raw materials requires more than vibrant political messages; it requires a profound revision of the concepts and technologies on which industrial chemical processes rely. Only a small fraction of molecules extracted from biomass bears significant chemical and commercial potentials to be considered as ubiquitous chemical platforms upon which a new, bio-based industry can thrive. Owing to its inherent assets in terms of unique process experience, scalability, and reduced environmental footprint, flow chemistry arguably has a major role to play in this context. This review covers a selection of C₂ to C₆ bio-based chemical platforms with existing commercial markets including polyols (ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, 1,4-butanediol, xylitol, and sorbitol), furanoids (furfural and 5-hydroxymethylfurfural) and carboxylic acids (lactic acid, succinic acid, fumaric acid, malic acid, itaconic acid, and levulinic acid). The aim of this review is to illustrate the various aspects of upgrading bio-based platform molecules toward commodity or specialty chemicals using new process concepts that fall under the umbrella of continuous flow technology and that could change the future perspectives of biorefineries.

Kinetic Modelling of the Coproduction Process of Fumaric and Malic Acids by Rhizopus arrhizus NRRL 1526

The production of organic acids by biotechnological processes has experienced a notable impulse with the advent of first and second generation biorefineries and the need of searching for renewable and sustainable feedstock, such as biomass. Fumaric acid is a promising biomonomer for polyamide production and a well-known acidulant and preservative in food and feed industries. Malic acid is a well-known food acidulant with a high market share. The biotechnological Fumaric and Malic acid production via fungi of the Rhizopus genus is being explored nowadays as a process for the valorization of food and food-related waste to obtain food ingredients and key platform chemicals of the so-called biochemical biorefinery. In this work, a preliminary study is performed to find reproducible conditions for the production of the acids by Rhizopus arrhizus NRRL 1526 by controlling fungi morphology and inoculum conditions. Afterwards, several production runs are performed to obtain biomass, glucose, and acid concentration data at different processing time values. Finally, an unstructured, unsegregated model including a logistic-type equation for biomass and potential-type equations for the substrate and the products is fitted to experimental data. We find that the production of the organic acids is mainly non-associated with fungal growth.

Fumarate production with Rhizopus oryzae: utilising the Crabtree effect to minimise ethanol by-product formation

BACKGROUND

The four-carbon dicarboxylic acids of the tricarboxylic acid cycle (malate, fumarate and succinate) remain promising bio-based alternatives to various precursor chemicals derived from fossil-based feed stocks. The double carbon bond in fumarate, in addition to the two terminal carboxylic groups, opens up an array of downstream reaction possibilities, where replacement options for petrochemical derived maleic anhydride are worth mentioning. To date the most promising organism for producing fumarate is Rhizopus oryzae (ATCC 20344, also referred to as Rhizopus delemar) that naturally excretes fumarate under nitrogen-limited conditions. Fumarate excretion in R. oryzae is always associated with the co-excretion of ethanol, an unwanted metabolic product from the fermentation. Attempts to eliminate ethanol production classically focus on enhanced oxygen availability within the mycelium matrix. In this study our immobilised R. oryzae process was employed to investigate and utilise the Crabtree characteristics of the organism in order to establish the limits of ethanol by-product formation under growth and non-growth conditions.

RESULTS

All fermentations were performed with either nitrogen excess (growth phase) or nitrogen limitation (production phase) where medium replacements were done between the growth and the production phase. Initial experiments employed excess glucose for both growth and production, while the oxygen partial pressure was varied between a dissolved oxygen of 18.4% and 85%. Ethanol was formed during both growth and production phases and the oxygen partial pressure had zero influence on the response. Results clearly indicated that possible anaerobic zones within the mycelium were not responsible for ethanol formation, hinting that ethanol is formed under fully aerobic conditions as a metabolic overflow product. For Crabtree-positive organisms like Saccharomyces cerevisiae ethanol overflow is manipulated by controlling the glucose input to the fermentation. The same strategy was employed for R. oryzae for both growth and production fermentations. It was shown that all ethanol can be eliminated during growth for a glucose addition rate of 0.07 g L - 1 h - 1 . The production phase behaved in a similar manner, where glucose addition of 0.197 g L - 1 h - 1 resulted in fumarate production of 0.150 g L - 1 h - 1 and a yield of 0.802 g g - 1 fumarate on glucose. Further investigation into the effect of glucose addition revealed that ethanol overflow commences at a glucose addition rate of 0.395 g g - 1 h - 1 on biomass, while the maximum glucose uptake rate was established to be between 0.426 and 0.533 g g - 1 h - 1 .

CONCLUSIONS

The results conclusively prove that R. oryzae is a Crabtree-positive organism and that the characteristic can be utilised to completely discard ethanol by-product formation. A state referred to as "homofumarate production" was illustrated, where all carbon input exits the cell as either fumarate or respiratory CO 2 . The highest biomass-based "homofumarate production": rate of 0.243 g g - 1 h - 1 achieved a yield of 0.802 g g - 1 on glucose, indicating the bounds for developing an ethanol free process. The control strategy employed in this study in conjunction with the uncomplicated scalability of the immobilised process provides new direction for further developing bio-fumarate production.

Microwave-assisted extraction of chitosan from Rhizopus oryzae NRRL 1526 biomass

Microwave-assisted extraction (MAE) of chitosan from dried fungal biomass of Rhizopus oryzae NRRL1526, obtained by culturing on potato dextrose broth (PDB), was performed and the optimal conditions required were identified using statistical analysis for the first time in this study. This microwave-assisted extraction (MAE) was compared against the conventional autoclave assisted method of chitosan extraction. The full factorial experimental design was used to investigate the impact of operating parameters of MAE, microwave power (100 W-500 W), and duration (10 min-30 min), on alkaline insoluble material (AIM) yield, chitosan yield, and degree of deacetylation (DDA). The effect of operating conditions was then evaluated using full factorial data analysis and optimum condition for MAE of chitosan was identified using response surface methodology to be 300 W and 22 min. This optimum condition identified was then further evaluated and the chitosan obtained characterized. Higher chitosan yield of 13.43 ± 0.3% (w/w) of fungal biomass was obtained when compared to that obtained, 6.67% ± 0.3% (w/w) of dry biomass, for the conventional extraction process. MAE yielded chitosan of higher degree of deacetylation, 94.6 ± 0.9% against 90.6 ± 0.5% (conventional heating), but the molecular weight was observed to be similar to that obtained by using conventional autoclave heating. MAE of chitosan was observed to yield a higher quantity of chitosan when compared to conventional extraction process and obtained chitosan exhibited a higher degree of deacetylation as well as molecular weight. The lower energy consumption of 0.11 kW h for MAE (5 kW h for conventional process) and the concomitant reduction in the energy bill to 1.1 cents from 50 cents, in addition to the above results, show that microwave irradiation is a more efficient and environment-friendly means to obtain chitosan from fungal biomass.