Xylitol production by Debaryomyces hansenii and Candida guilliermondii from rapeseed straw hemicellulosic hydrolysate

Enhancing 2,3-butanediol and acetoin production from brewer's spent grain hemicellulosic hydrolysate through bacterial co-cultivation

This study evaluated bacterial co-cultivation as a strategy to mitigate brewer's spent grain (BSG) hemicellulosic hydrolysate toxicity, aiming to enhance 2,3-butanediol (2,3-BDO) and acetoin production through fermentation. Co-culture of Paenibacillus polymyxa with Pseudomonas alloputida or Rhodococcus sp. was assessed using synthetic medium and BSG hydrolysate. Attention was given to removing inhibitory compounds, including lignin-derived phenolics, hydroxymethylfurfural, furfural, and acetic acid, through microbial detoxification during co-cultivation. Various fermentation temperatures (30, 34, and 37 °C) and initial cell concentrations (OD600 of 0.05 and 0.1) were tested. Both P. polymyxa and Rhodococcus sp. effectively removed inhibitory compounds present in the medium. Co-cultures with Rhodococcus sp. exhibited higher sugar consumption rates (1.01 vs 0.88 g/L·h) than P. polymyxa monoculture, efficiently utilizing glucose, xylose, and arabinose, producing 2,3-BDO and acetoin. In co-culture with Rhodococcus sp., concentration (3.7 g/L), yield (0.14 g/g) and productivity (0.10 g/L·h) of 2,3-BDO at 34 °C considerably surpassed that of the P. polymyxa monoculture, with an increase of up to 48 %. These findings highlight the potential of co-cultures, especially with Rhodococcus sp., to alleviate inhibitory compound impacts when using complex media for fermentation. This study represents the first exploration of 2,3-BDO and acetoin production from BSG hemicellulosic hydrolysates using co-cultures.

Current Directions of Selected Plant-Origin Wastes' Valorization in Biotechnology of Food Additives and Other Important Chemicals

Environmental pollution and the accumulation of industrial waste are increasingly serious issues that impose financial burdens on businesses and pose threats to ecosystems. As industrial production continues to grow, the volume of waste generated by humanity is rising, leading to a heightened need to search for effective waste management and recycling methods. One promising approach is the concept of a circular economy, where industrial waste, including agricultural and food processing waste, is transformed into new products. The goal is to maximize the utilization of natural resources, particularly in food production. This article presents various concepts for utilizing specific types of plant-based waste, particularly lignocellulosic, pectin, and starch wastes, in biotechnological processes aimed at producing value-added food ingredients with a technological function. The literature clearly shows that this waste can be effectively used in the cultivation of different microorganisms to produce enzymes, polyols, oligosaccharides, carboxylic acids, and biopolymers, among other products. However, further research is needed to explore more efficient and environmentally friendly methods, especially in the utilization of lignocellulose in biotechnology. This research shows knowledge gaps in existing discussed solutions.

Membrane-based processes for xylitol production from oil palm empty fruit bunches hydrolysate fermentation broth

Oil palm empty fruit bunch (OPEFB) is one of the wastes that has high hemicellulose composition and potentially processed into xylitol via biotransformation route. This study explores the effectiveness of ultrafiltration (UF) and nanofiltration (NF) in purifying and concentrating xylitol from OPEFB hydrolysate-fermentation broth. Various UF membranes, including UF1 (MWCO 150 kDa), UF2-Psf (MWCO 20 kDa), and UF2-PVDF (MWCO 50 kDa), were used, along with NF (MWCO 150 Da). Pre-treating the broth before UF was crucial to remove foulants such as microorganisms and macromolecules. While microfiltration (MF) achieved 100% microorganism rejection, its flux declined rapidly, necessitating feed centrifugation before MF. The choice of UF membrane MWCO significantly influenced xylitol retention, with UF2-PSf leading to substantial xylitol loss and UF2-PVDF showed promising results. NF has shown its applicability in concentrating xylitol in the UF permeate as much as 4 times higher, while permeating 90% of the acetic adic in the solution.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-024-06044-7.

Exploring the complexity of xylitol production in the fungal cell factory Aspergillus niger

Production of xylitol from agricultural by-products offers a promising approach for the circular bioeconomy. This study investigates the roles of transcription factors XlnR and CreA in xylitol production from wheat bran in Aspergillus niger by generating strains with a constitutively active XlnR (XlnRc, V756F mutation) and/or deletion of creA, in a previously generated xylitol-producing strain. The XlnRc mutation increased the initial rate of xylitol production but lowered the overall accumulation. Deletion of creA in this strain significantly improved both the onset and rate of xylitol production, indicating an inhibitory role of CreA in the PCP. These results demonstrate the complexity of metabolic engineering to generate fungal cell factories for valuable biochemicals, such as xylitol, as not only metabolic but also multiple gene regulation aspects need to be considered.

Aspergillus labruscus ITAL 22.223 xylanase - immobilization and application for the obtainment of corncob xylan targeting xylitol production

Corncob is an agro-residue rich in lignocellulosic material that can be used for the xylitol production, through its enzymatic conversion obtaining fermentable sugars and their subsequent fermentation. In light of the above, this study targeted the immobilization of Aspergillus labruscus xylanase and the use of the derivative to hydrolyze the corncob xylan for the obtainment of xylose, and its subsequent use for the production of xylitol. The extracellular xylanase was immobilized using different supports (sodium alginate, DEAE-Cellulose, DEAE-Sephadex and CM-Sephadex). Among all supports used, the best results were obtained with the DEAE-Cellulose derivative showing an efficiency of immobilization of 97-99%, yield of 93-95% and recovered activity of 81-100%. The sodium alginate derivative showed 3 cycles of reuse, with drop in activity of about 65% in the 3rd cycle using both CaCl2 and MnCl2 as crosslinkers. The best enzymatic activity for the DEAE-Cellulose derivative was observed at 55ºC and pH 5.0. This derivative presented reuse of 10 cycles using commercial xylan as substrate, and 4 cycles using corncob xylan. This derivative was used in an enzymatic reactor to hydrolyze corncob xylan, obtaining 2.7 mg/mL of xylose after 48 h of operation under optimal condition of temperature and pH. The xylose obtained from the corncob was fermented by Candida tropicalis for 96 h with consumption of 60%. The HPLC analyses indicated a production of 1.02 mg/mL of xylitol with 48 h of fermentation. In conclusion, this is the first report on the immobilization of the A. labrucus xylanase as an alternative for the obtainment of xylose from corncob xylan, and the subsequent production of xylitol.

Research progress in the biosynthesis of xylitol: feedstock evolution from xylose to glucose

Xylitol, as an important food additive and fine chemical, has a wide range of applications, including food, medicine, chemical, and feed. This review paper focuses on the research progress of xylitol biosynthesis, from overcoming the limitations of traditional chemical hydrogenation and xylose bioconversion, to the full biosynthesis of xylitol production using green and non-polluting glucose as substrate. In the review, the molecular strategies of wild strains to increase xylitol yield, as well as the optimization strategies and metabolic reconfiguration during xylitol biosynthesis are discussed. Subsequently, on the basis of existing studies, the paper further discusses the current status of research and future perspectives of xylitol production using glucose as a single substrate. The evolution of raw materials from xylose-based five-carbon sugars to glucose is not only cost-saving, but also safe and environmentally friendly, which brings new opportunities for the green industrial chain of xylitol.

Improved xylitol production by the novel inhibitor-tolerant yeast Candida tropicalis K2

Production of potential value-added products from different lignocellulosic biomass is becoming more common due to the availability of the feedstocks in abundance and the environment- friendly nature of the microbial production process. Due to the large array of its applications in the pharmaceutical and food sectors, xylitol is considered as potential value-added compound for production. In this study, organic waste samples were collected from various habitats and screened for potential yeast isolates for xylitol production. Among 124 tested isolates, Candida tropicalis K2 showed the highest potential for xylitol production as well as inhibitors tolerance (Furfural, 5-hydroxymethyl furfural and acetic acid) phenotypes. C. tropicalis K2 produced 90 g/L of xylitol in batch fermentation (100 g/L xylose supplemented with 20 g/L of glycerol as co-substrate) with the yield and productivity of 0.90 g/g and 1.5 g/L.h, respectively, at pH 5.5 and 30°C temperature. Together, >10% higher xylitol yield was achieved when glycerol was used as a co-substrate with pure xylose. Moreover, with non-detoxified corncob and Albizia pod hydrolysates, C. tropicalis K2 isolate produced 0.62 and 0.69 g/g of xylitol yields and 1.04 and 0.75 g/L.h xylitol productivities, respectively. Thus, C. tropicalis K2 isolate could be considered as promising candidate for xylitol production from different lignocellulosic biomass.HIGHLIGHTS Candia tropicalis K2 isolate was screened from natural sites of biomass degradation and characterized for xylitol production.Non-detoxified Albizia pod and corncob hydrolysates were explored for xylitol production using selected C. tropicalis K2 isolate.A maximum of 0.90 g/g yield and 1.07 g/L.h xylitol productivity was achieved with pure xylose.A >10% increase in xylitol yield was achieved using glycerol as a co-substrate.

Open (non-sterile) cultivations of Debaryomyces hansenii for recombinant protein production combining industrial side-streams with high salt content

The halotolerant non-conventional yeast Debaryomyces hansenii can grow in media containing high concentrations of salt (up to 4 M), metabolize alternative carbon sources than glucose, such as lactose or glycerol, and withstand a wide range of temperatures and pH. These inherent capabilities allow this yeast to grow in harsh environments and use alternative feedstock than traditional commercial media. For example, D. hansenii could be a potential cell factory for revalorizing industrial salty by-products, using them as a substrate for producing new valuable bioproducts, boosting a circular economy. In this work, three different salty by-products derived from the dairy and biopharmaceutical industry have been tested as a possible feedstock for D. hansenii's growth. The yeast was not only able to grow efficiently in all of them but also to produce a recombinant protein (Yellow Fluorescent Protein, used as a model) without altering its performance. Moreover, open cultivations at different laboratory scales (1.5 mL and 1 L) were performed under non-sterile conditions and without adding fresh water or any nutritional supplement to the cultivation, making the process cheaper and more sustainable.

Expanding sugar alcohol industry: Microbial production of sugar alcohols and associated chemocatalytic derivatives

Sugar alcohols are polyols that are widely employed in the production of chemicals, pharmaceuticals, and food products. Chemical synthesis of polyols, however, is complex and necessitates the use of hazardous compounds. Therefore, the use of microbes to produce polyols has been proposed as an alternative to traditional synthesis strategies. Many biotechnological approaches have been described to enhancing sugar alcohols production and microbe-mediated sugar alcohol production has the potential to benefit from the availability of inexpensive substrate inputs. Among of them, microbe-mediated erythritol production has been implemented in an industrial scale, but microbial growth and substrate conversion rates are often limited by harsh environmental conditions. In this review, we focused on xylitol, mannitol, sorbitol, and erythritol, the four representative sugar alcohols. The main metabolic engineering strategies, such as regulation of key genes and cofactor balancing, for improving the production of these sugar alcohols were reviewed. The feasible strategies to enhance the stress tolerance of chassis cells, especially thermotolerance, were also summarized. Different low-cost substrates like glycerol, molasses, cellulose hydrolysate, and CO₂ employed for producing these sugar alcohols were presented. Given the value of polyols as precursor platform chemicals that can be leveraged to produce a diverse array of chemical products, we not only discuss the challenges encountered in the above parts, but also envisioned the development of their derivatives for broadening the application of sugar alcohols.

Relation of xylitol formation and lignocellulose degradation in yeast

One of the critical steps of the biotechnological production of xylitol from lignocellulosic biomass is the deconstruction of the plant cell wall. This step is crucial to the bioprocess once the solubilization of xylose from hemicellulose is allowed, which can be easily converted to xylitol by pentose-assimilating yeasts in a microaerobic environment. However, lignocellulosic toxic compounds formed/released during plant cell wall pretreatment, such as aliphatic acids, furans, and phenolic compounds, inhibit xylitol production during fermentation, reducing the fermentative performance of yeasts and impairing the bioprocess productivity. Although the toxicity of lignocellulosic inhibitors is one of the biggest bottlenecks of the biotechnological production of xylitol, most of the studies focus on how much xylitol production is inhibited but not how and where cells are affected. Understanding this mechanism is important in order to develop strategies to overcome lignocellulosic inhibitor toxicity. In this mini-review, we addressed how these inhibitors affect both yeast physiology and metabolism and consequently xylose-to-xylitol bioconversion. In addition, this work also addresses about cellular adaptation, one of the most relevant strategies to overcome lignocellulosic inhibitors toxicity, once it allows the development of robust and tolerant strains, contributing to the improvement of the microbial performance against hemicellulosic hydrolysates toxicity. KEY POINTS: • Impact of lignocellulosic inhibitors on the xylitol production by yeasts • Physiological and metabolic alterations provoked by lignocellulosic inhibitors • Cell adaptation as an efficient strategy to improve yeast's robustness.

Strategy to reduce acetic acid in sugarcane bagasse hemicellulose hydrolysate concomitantly with xylitol production by the promising yeast Cyberlindnera xylosilytica in a bioreactor

The yeast Cyberlindnera xylosilytica UFMG-CM-Y309 has been identified as a promising new xylitol producer from sugarcane bagasse hemicellulosic hydrolysate (SCHH). However, SCHH pretreatment process generates byproducts, which are toxic to cell metabolism, including furans, phenolic compounds, and carboxylic acids, such as acetic acid, typically released at high concentrations. This research aims to reduce acetic acid in sugarcane hemicellulose hydrolysate concomitantly with xylitol production by yeast strain Cy. xylosilytica UFMG-CM-Y309 in a bioreactor by strategically evaluating the influence of volumetric oxygen transfer coefficient (k_La) (21 and 35 h^-1). Experiments were conducted on a bench bioreactor (2 L volumetric capacity) at different initial k_La values (21 and 35 h^-1). SCHH medium was supplemented with rice bran extract (10 g L^-1) and yeast extract (1 g L^-1). Cy. xylosilytica showed high xylitol production performance (19.56 g L^-1), xylitol yield (0.56 g g^-1) and, maximum xylitol-specific production rate (μp_máx 0.20 g_xylitol·g^-1 h^-1) at k_La value of 21 h^-1, concomitantly slowing the rate of acetic acid consumption. A faster acetic acid consumption (100%) by Cy. xylosilytica was observed at k_La of 35 h^-1, concomitantly with an increase in maximum cellular growth (14.60 g L^-1) and reduction in maximum xylitol production (14.56 g L^-1 and Y_p/s 0.34 g g^-1). This study contributes to pioneering research regarding this yeast performance in bioreactors, emphasizing culture medium detoxification and xylitol production.

Utilization of salt-rich by-products from the dairy industry as feedstock for recombinant protein production by Debaryomyces hansenii

The dairy industry processes vast amounts of milk and generates high amounts of secondary by-products, which are still rich in nutrients (high Chemical Oxygen Demand (COD) and Biochemical Oxygen Demand (BOD) levels) but contain high concentrations of salt. The current European legislation only allows disposing of these effluents directly into the waterways with previous treatment, which is laborious and expensive. Therefore, as much as possible, these by-products are reutilized as animal feed material and, if not applicable, used as fertilizers adding phosphorus, potassium, nitrogen, and other nutrients to the soil. Finding biological alternatives to revalue dairy by-products is of crucial interest in order to improve the utilization of dry dairy matter and reduce the environmental impact of every litre of milk produced. Debaryomyces hansenii is a halotolerant non-conventional yeast with high potential for this purpose. It presents some beneficial traits - capacity to metabolize a variety of sugars, tolerance to high osmotic environments, resistance to extreme temperatures and pHs - that make this yeast a well-suited option to grow using complex feedstock, such as industrial waste, instead of the traditional commercial media. In this work, we study for the first time D. hansenii's ability to grow and produce a recombinant protein (YFP) from dairy saline whey by-products. Cultivations at different scales (1.5, 100 and 500 ml) were performed without neither sterilizing the medium nor using pure water. Our results conclude that D. hansenii is able to perform well and produce YFP in the aforementioned salty substrate. Interestingly, it is able to outcompete other microorganisms present in the waste without altering its cell performance or protein production capacity.

Fermentation performance of a Mexican native Clavispora lusitaniae strain for xylitol and ethanol production from xylose, glucose and cellobiose

Lignocellulose hydrolysates are rich in fermentable sugars such as xylose, cellobiose and glucose, with high potential in the biotechnology industry to obtain bioproducts of higher economic value. Thus, it is important to search for and study new yeast strains that co-consume these sugars to achieve better yields and productivity in the processes. The yeast Clavispora lusitaniae CDBB-L-2031, a native strain isolated from mezcal must, was studied under various culture conditions to potentially produce ethanol and xylitol due to its ability to assimilate xylose, cellobiose and glucose. This yeast produced ethanol under microaerobic conditions with yields of 0.451 g_ethanol/g_glucose and 0.344 g_ethanol/g_cellobiose, when grown on 1% glucose or cellobiose, respectively. In mixtures (0.5% each) of glucose:xylose and glucose:xylose:cellobiose the yields were 0.367 g_ethanol/g_GX and 0. 380 g_ethanol/g_GXC, respectively. Likewise, in identical conditions, C. lusitaniae produced xylitol from xylose with a yield of 0.421 g_xylitol/g_xylose. In 5% glucose or xylose, this yeast had better ethanol and xylitol titers and yields, respectively. However, glucose negatively affected xylitol production in the mixture of both sugars (3% each), producing only ethanol. Xylose reductase (XR) and xylitol dehydrogenase (XDH) activities were evaluated in cultures growing on xylose or glucose, obtaining the highest values in cultures on xylose at 8 h (25.9 and 6.22 mU/mg, respectively). While in glucose cultures, XR and XDH activities were detected once this substrate was consumed (4.06 and 3.32 mU/mg, respectively). Finally, the XYL1 and XYL2 genes encoding xylose reductase and xylitol dehydrogenase, respectively, were up-regulated by xylose, whereas glucose down-regulated their expression.

Debaryomyces hansenii: an old acquaintance for a fresh start in the era of the green biotechnology

The halophilic yeast Debaryomyces hansenii has been studied for several decades, serving as eukaryotic model for understanding salt and osmotic tolerance. Nevertheless, lack of consensus among different studies is found and, sometimes, contradictory information derived from studies performed in very diverse conditions. These two factors hampered its establishment as the key biotechnological player that was called to be in the past decade. On top of that, very limited (often deficient) engineering tools are available for this yeast. Fortunately Debaryomyces is again gaining momentum and recent advances using highly instrumented lab scale bioreactors, together with advanced –omics and HT-robotics, have revealed a new set of interesting results. Those forecast a very promising future for D. hansenii in the era of the so-called green biotechnology. Moreover, novel genetic tools enabling precise gene editing on this yeast are now available. In this review, we highlight the most recent developments, which include the identification of a novel gene implicated in salt tolerance, a newly proposed survival mechanism for D. hansenii at very high salt and limiting nutrient concentrations, and its utilization as production host in biotechnological processes.

Yeasts Inhabiting Extreme Environments and Their Biotechnological Applications

Yeasts are microscopic fungi inhabiting all Earth environments, including those inhospitable for most life forms, considered extreme environments. According to their habitats, yeasts could be extremotolerant or extremophiles. Some are polyextremophiles, depending on their growth capacity, tolerance, and survival in the face of their habitat's physical and chemical constitution. The extreme yeasts are relevant for the industrial production of value-added compounds, such as biofuels, lipids, carotenoids, recombinant proteins, enzymes, among others. This review calls attention to the importance of yeasts inhabiting extreme environments, including metabolic and adaptive aspects to tolerate conditions of cold, heat, water availability, pH, salinity, osmolarity, UV radiation, and metal toxicity, which are relevant for biotechnological applications. We explore the habitats of extreme yeasts, highlighting key species, physiology, adaptations, and molecular identification. Finally, we summarize several findings related to the industrially-important extremophilic yeasts and describe current trends in biotechnological applications that will impact the bioeconomy.

Activation of cryptic xylose metabolism by a transcriptional activator Znf1 boosts up xylitol production in the engineered Saccharomyces cerevisiae lacking xylose suppressor BUD21 gene

Background

Xylitol is a valuable pentose sugar alcohol, used in the food and pharmaceutical industries. Biotechnological xylitol production is currently attractive due to possible conversion from abundant and low-cost industrial wastes or agricultural lignocellulosic biomass. In this study, the transcription factor Znf1 was characterised as being responsible for the activation of cryptic xylose metabolism in a poor xylose-assimilating S. cerevisiae for xylitol production.

Results

The results suggest that the expression of several xylose-utilising enzyme genes, encoding xylose reductases for the reduction of xylose to xylitol was derepressed by xylose. Their expression and those of a pentose phosphate shunt and related pathways required for xylose utilisation were strongly activated by the transcription factor Znf1. Using an engineered S. cerevisiae strain overexpressing ZNF1 in the absence of the xylose suppressor bud21Δ, xylitol production was maximally by approximately 1200% to 12.14 g/L of xylitol, corresponding to 0.23 g/g xylose consumed, during 10% (w/v) xylose fermentation. Proteomic analysis supported the role of Znf1 and Bud21 in modulating levels of proteins associated with carbon metabolism, xylose utilisation, ribosomal protein synthesis, and others. Increased tolerance to lignocellulosic inhibitors and improved cell dry weight were also observed in this engineered bud21∆ + pLJ529-ZNF1 strain. A similar xylitol yield was achieved using fungus-pretreated rice straw hydrolysate as an eco-friendly and low-cost substrate.

Conclusions

Thus, we identified the key modulators of pentose sugar metabolism, namely the transcription factor Znf1 and the suppressor Bud21, for enhanced xylose utilisation, providing a potential application of a generally recognised as safe yeast in supporting the sugar industry and the sustainable lignocellulose-based bioeconomy.

Graphical Abstract

Utilizing yeasts for the conversion of renewable feedstocks to sugar alcohols - a review

Sugar alcohols are widely marketed compounds. They are useful building block chemicals and of particular value as low- or non-calorigenic sweeteners, serving as sugar substitutes in the food industry. To date most sugar alcohols are produced by chemical routes using pure sugars, but a transition towards the use of renewable, non-edible feedstocks is anticipated. Several yeasts are naturally able to convert renewable feedstocks, such as lignocellulosic substrates, glycerol and molasses, into sugar alcohols. These bioconversions often face difficulties to obtain sufficiently high yields and productivities necessary for industrialization. This review provides insight into the most recent studies on utilizing yeasts for the conversion of renewable feedstocks to diverse sugar alcohols, including xylitol, erythritol, mannitol and arabitol. Moreover, metabolic approaches are highlighted that specifically target shortcomings of sugar alcohol production by yeasts from these renewable substrates.

An overview of the metabolically engineered strains and innovative processes used for the value addition of biomass derived xylose to xylitol and xylonic acid

Xylose, the most abundant pentose sugar of the hemicellulosic fraction of lignocellulosic biomass, has to be utilized rationally for the commercial viability of biorefineries. An effective pre-treatment strategy for the release of xylose from the biomass and an appropriate microbe of the status of an Industrial strain for the utilization of this pentose sugar are key challenges which need special attention for the economic success of the biomass value addition to chemicals. Xylitol and xylonic acid, the alcohol and acid derivatives of xylose are highly demanded commodity chemicals globally with plenty of applications in the food and pharma industries. This review emphasis on the natural and metabolically engineered strains utilizing xylose and the progressive and innovative fermentation strategies for the production and subsequent recovery of the above said chemicals from pre-treated biomass medium.

Microbial xylitol production

Xylitol is pentahydroxy sugar alcohol, existing in very trace amount in fruits and vegetables, and finds varied application in industries like food, pharmaceuticals, confectionaries, etc. and is of prime importance to health. Owing to its trace occurrence in nature and considerable increase in market demand that exceeds availability, alternate production through biotechnological and chemical approach is in process. Biochemical production involves substrates like lignocellulosic biomasses and industrial effluents and is an eco-friendly process with high dependency on physico-chemical parameters. Although the chemical processes are faster, high yielding and economical, they have a great limitation as usage of toxic chemicals and thus need to be regulated and replaced by an environment friendly approach. Microbes play a major role in xylitol production through a biotechnological process towards the development of a sustainable system. Major microbes working on assimilation of xylose for production of xylitol include Candida tropicalis, Candida maltose, Bacillus subtilis, Debaromyces hansenii, etc. The present review reports all probable microbial xylitol production biochemical pathways encompassing diverse bioprocesses involved in uptake and conversion of xylose sugars from agricultural residues and industrial effluents. A comprehensive report on xylitol occurrence and biotechnological production processes with varied substrates has been encompassed. KEY POINTS: • Xylitol from agro-industrial waste • Microbial xylose assimilation.

High level xylitol production by Pichia fermentans using non-detoxified xylose-rich sugarcane bagasse and olive pits hydrolysates

Hemicellulosic sugars, the overlooked fraction of lignocellulosic residues can serve as potential and cost-effective raw material that can be exploited for xylitol production. Xylitol is a top platform chemical with applications in food and pharmaceutical industries. Sugarcane bagasse (SCB) and olive pits (OP) are the major waste streams from sugar and olive oil industries, respectively. The current study evaluated the potential of Pichia fermentans for manufacturing of xylitol from SCB and OP hydrolysates through co-fermentation strategy. The highest xylitol accumulation was noticed with a glucose and xylose ratio of 1:10 followed by feeding with xylose alone. The fed-batch cultivation using pure xylose, SCB, and OP hydrolysates, resulted in xylitol accumulation of 102.5, 86.6 and 71.9 g/L with conversion yield of 0.78, 0.75 and 0.74 g/g, respectively. The non-pathogenic behaviour and ability to accumulate high xylitol levels from agro-industrial residues demonstrates the potential of P. fermentans as microbial cell factory.

Xylitol Production by Candida Species from Hydrolysates of Agricultural Residues and Grasses

Xylitol is an industrially important chemical due to its commercial applications. The use of xylitol as a sweetener as well as its utilization in biomedical applications has made it a high value specialty chemical. Although several species of yeast synthesize xylitol, this review focusses on the species of the genus Candida. The importance of the enzyme xylitol reductase present in Candida species as it relates to their ability to synthesize xylitol was examined. Another focus of this work was to review prior studies examining the ability of the Candida species to synthesize xylitol effectively from hydrolysates of agricultural residues and grasses. An advantage of utilizing such a hydrolysate as a substrate for yeast xylitol production would be decreasing the overall cost of synthesizing xylitol. The intent of this review was to learn if such hydrolysates could substitute for xylose as a substrate for the yeast when producing xylitol. In addition, a comparison of xylitol production by Candida species should indicate which hydrolysate of agricultural residues and grasses would be the best substrate for xylitol production. From studies analyzing previous hydrolysates of agricultural residues and grasses, it was concluded that a hydrolysate of sugarcane bagasse supported the highest level of xylitol by Candida species, although corncob hydrolysates also supported significant yeast xylitol production. It was also concluded that fewer studies examined yeast xylitol production on hydrolysates of grasses and that further research on grasses may provide hydrolysates with a higher xylose content, which could support greater yeast xylitol production.

Increasing NADPH Availability for Xylitol Production via Pentose-Phosphate-Pathway Gene Overexpression and Embden-Meyerhof-Parnas-Pathway Gene Deletion in Escherichia coli

Cofactor availability is often a rate-limiting factor in the bioconversion of xylose to xylitol. The overexpression of pentose phosphate pathway genes and the deletion of Embden-Meyerhof-Parnas pathway genes can modulate the glucose metabolic flux and increase the intracellular NADPH supply, enabling Escherichia coli cells to produce xylitol from corncob hydrolysates. The effects of zwf and/or gnd overexpression and pfkA, pfkB, and/or pgi deletion on the intracellular redox environment and xylitol production were examined. The NADPH-enhanced strain 2bpgi produced 162 g/L xylitol from corncob hydrolysates after a 76 h fed-batch fermentation in a 15 L bioreactor, which was 13.3% greater than the 143 g/L xylitol produced by the IS5-d control strain. Additionally, the xylitol productivity and xylitol yield per glucose for 2bpgi were 2.13 g/L/h and 2.50 g/g, respectively. Thus, the genetic modifications in 2bpgi significantly enhanced NADPH regeneration, making 2bpgi a potentially useful strain for the industrial-scale production of xylitol from detoxified corncob hydrolysates.

Development of a purification process via crystallization of xylitol produced for bioprocess using a hemicellulosic hydrolysate from the cashew apple bagasse as feedstock

Xylitol was biotechnologically produced by Kluyveromyces marxianus ATCC36907 using the hemicellulosic hydrolysate of the cashew apple bagasse (CABHH). Sequentially, the present study investigated the recovery and purification of xylitol evaluating different antisolvents [ethanol, isopropanol and the ionic liquid 2-hydroxyl-ethylammonium acetate (2-HEAA)], their proportion in the medium (10-90% v/v), and their cooling rate (V_C 0.25-0.50 °C/min). These processes were contrasted with the crystallization process of commercial xylitol. This study is the first to assess xylitol crystallization using a protic ionic liquid. The hydrolysate obtained from a mild treatment with sulfuric acid contained mainly glucose and xylose at concentrations of 15.7 g/L and 11.9 g/L, respectively. With this bioprocess, a maximum xylitol production of 4.5 g/L was achieved. The performance of the investigated antisolvents was similar in all conditions evaluated in the crystallization process of the commercial xylitol, with no significant difference in yields. For the crystallization processes of the produced xylitol, the best conditions were: 50% (v/v) isopropanol as antisolvent, cooling rate of 0.5 °C/min, with a secondary nucleation of yield and purity of 69.7% and 84.8%, respectively. Under the same linear cooling rate, using ethanol, isopropanol or the protic ionic liquid 2-hydroxyl-ethylammonium acetate (2-HEAA), crystallization did not occur, probably due to the presence of carbohydrates not metabolized by the yeast in the broth, which influences the solubility curve of xylitol. With the results of this work, a possible economical and environmentally friendly process of recovery and purification of xylitol from CABHH could be proposed.

Optimization of activated charcoal detoxification and concentration of chestnut shell hydrolysate for xylitol production

OBJECTIVES

To increase xylose concentration of the chestnut shell hemicellulosic hydrolysate with an acceptable phenolic compound level in order to enhance xylitol production by Candida tropicalis M43.

RESULTS

The xylose concentration and total phenolic compound concentration of the hydrolysate were obtained as 33.68 g/L and 77.38 mg gallic acid equivalent/L, respectively by optimization of detoxification parameters and concentration level (60 °C, 115 min contact time, 5.942% (w/v) dosage of activated charcoal, 120 strokes/min shaking rate and 0.2 volume ratio). Xylitol production was achieved in the hydrolysate by using Candida tropicalis M43. The maximum xylitol concentration was 6.30 g/L and productivity, yield and percentage of substrate conversion were calculated as 0.11 g/L h, 19.13% and 97.79%, respectively. In addition, the chestnut shell hydrolysate fortified with xylose and the maximum xylitol concentration increased to 18.08 g/L in the hydrolysate-based medium containing 80 g/L xylose.

CONCLUSIONS

Optimizing detoxification conditions with concentration level was found to be useful for enhancing xylitol production. In addition, fortification of the hydrolysate caused a three fold increase in maximum xylitol concentration.

Potential for reduced water consumption in biorefining of lignocellulosic biomass to bioethanol and biogas

Increasing ethanol demand and public concerns about environmental protection promote the production of lignocellulosic bioethanol. Compared to that of starch- and sugar-based bioethanol production, the production of lignocellulosic bioethanol is water-intensive. A large amount of water is consumed during pretreatment, detoxification, saccharification, and fermentation. Water is a limited resource, and very high water consumption limits the industrial production of lignocellulosic bioethanol and decreases its environmental feasibility. In this review, we focused on the potential for reducing water consumption during the production of lignocellulosic bioethanol by performing pretreatment and fermentation at high solid loading, omitting water washing after pretreatment, and recycling wastewater by integrating bioethanol production and anaerobic digestion. In addition, the feasibility of these approaches and their research progress were discussed. This comprehensive review is expected to draw attention to water competition between bioethanol production and human use.

Development of a purification process via crystallization of xylitol produced for bioprocess using a hemicellulosic hydrolysate from the cashew apple bagasse as feedstock

Xylitol was biotechnologically produced by Kluyveromyces marxianus ATCC36907 using the hemicellulosic hydrolysate of the cashew apple bagasse (CABHH). Sequentially, the present study investigated the recovery and purification of xylitol evaluating different antisolvents [ethanol, isopropanol and the ionic liquid 2-hydroxyl-ethylammonium acetate (2-HEAA)], their proportion in the medium (10-90% v/v), and their cooling rate (V_C 0.25-0.50 °C/min). These processes were contrasted with the crystallization process of commercial xylitol. This study is the first to assess xylitol crystallization using a protic ionic liquid. The hydrolysate obtained from a mild treatment with sulfuric acid contained mainly glucose and xylose at concentrations of 15.7 g/L and 11.9 g/L, respectively. With this bioprocess, a maximum xylitol production of 4.5 g/L was achieved. The performance of the investigated antisolvents was similar in all conditions evaluated in the crystallization process of the commercial xylitol, with no significant difference in yields. For the crystallization processes of the produced xylitol, the best conditions were: 50% (v/v) isopropanol as antisolvent, cooling rate of 0.5 °C/min, with a secondary nucleation of yield and purity of 69.7% and 84.8%, respectively. Under the same linear cooling rate, using ethanol, isopropanol or the protic ionic liquid 2-hydroxyl-ethylammonium acetate (2-HEAA), crystallization did not occur, probably due to the presence of carbohydrates not metabolized by the yeast in the broth, which influences the solubility curve of xylitol. With the results of this work, a possible economical and environmentally friendly process of recovery and purification of xylitol from CABHH could be proposed.

Process scale-up of an efficient acid-catalyzed steam pretreatment of rice straw for xylitol production by C. Tropicalis MTCC 6192

The present study focuses on operational parameters for the efficient acid catalyzed rice straw pretreatment process for xylitol production. 75.77 % xylose yield was attained when the 24 h presoaked rice straw (≤10 mm or ≤ 15 mm) in 1.5 % (v/v) H₂SO₄ was pretreated in the same reactor at 121 °C for 30 min. Neutralization with barium hydroxide produced insoluble salt and noticeably reduced HMF and furfurals. Xylitol yield of 0.6 g/g of xylose, was achieved by fermenting rice straw hydrolysate medium with C. tropicalis MTCC 6192. This two-step process of production of xylitol from xylose rich hydrolysate is much simpler and produced minimal inhibitors including organic acids such as acetic acid. This process is modified for upscaling at optimized parameters and will simultaneously minimize the pollution problem caused by rice straw and is also promising for commercial scale.

Effect of pH on xylitol production by Candida species from a prairie cordgrass hydrolysate

Using hydrolysates of the North American prairie grass prairie cordgrass buffered at pH 4.5, 5.0, 5.5 or 6.0, xylitol production, xylitol yield, cell biomass production and productivity were investigated for three strains of yeast Candida. Of the three strains, the highest xylitol concentration of 20.19 g xylitol (g xylose consumed)-1 and yield of 0.89 g xylitol (g xylose consumed)-1 were produced by Candida mogi ATCC 18364 when grown for 120 h at 30° C on the pH 5.5-buffered hydrolysate-containing medium. The highest biomass level being 7.7 g cells (kg biomass)-1 was observed to be synthesized by Candida guilliermondii ATCC 201935 after 120 h of growth at 30° C on a pH 5.5-buffered hydrolysate-containing medium. The highest xylitol specific productivity of 0.73 g xylitol (g cells h)-1 was determined for C. guilliermondii ATCC 20216 after 120 h of growth at 30°C on a pH 5.0-buffered hydrolysate-containing medium. Xylitol production and yield by the three Candida strains was higher on prairie cordgrass than what was previously observed for the same strains after 120 h at 30° C when another North American prairie grass big bluestem served as the plant biomass hydrolysate indicating that prairie cordgrass may be a superior plant biomass substrate.

Xylitol Production from Exhausted Olive Pomace by Candida boidinii

In this work, the production of xylitol from a hemicellulosic hydrolysate of exhausted olive pomace (EOP), a residue originated in the olive oil production process by Candida boidinii, was assessed. The hydrolysate was obtained by dilute acid pretreatment of EOP at 170 °C and 2% H2SO4 (w/v). A previous detoxification step of the hydrolysate was necessary, and its treatment with activated charcoal and ion-exchange resin was evaluated. Prior to fermentation of the hydrolysate, fermentation tests in synthetic media were performed to determine the maximum xylitol yield and productivity that could be obtained if inhibitory compounds were not present in the medium. In addition, the glucose existing in the media exerted a negative influence on xylitol production. A maximum xylitol yield of 0.52 g/g could be achieved in absence of inhibitor compounds. Fermentation of the hemicellulosic hydrolysate from EOP after detoxification with ion-exchange resin resulted in a xylitol yield of 0.43 g/g.

Hydrolysis of Corncob Hemicellulose by Solid Acid Sulfated Zirconia and Its Evaluation in Xylitol Production

Corncob is an abundant agricultural residue containing high content of hemicellulose. In this paper, the hemicellulosic hydrolysate was prepared from the hydrolysis of corncob using the solid acid sulfated zirconia as a catalyst. According to response surface analysis experiments, the optimum conditions for preparing hemicellulosic hydrolysate catalyzed by sulfated zirconia were determined as follows: solid (sulfated zirconia)-solid (corncob) ratio was 0.33, solid (corncob)-liquid (water) ratio was 0.09, temperature was 153 °C, and time was 5.3 h. Under the optimized conditions, the soluble sugar concentration was 30.12 g/L with a yield of 033 g/g corncob. Subsequently, xylitol production from the resulting hemicellulosic hydrolysate was demonstrated by Candida tropicalis, and results showed that the yield of xylitol from the hemicellulosic hydrolysate could be significantly improved on a basis of decolorization and detoxification before fermentation. The maximum yield of xylitol from the hemicellulosic hydrolysate fermented by C. tropicalis was 0.76 g/g. This study provides a new attempt for xylitol production from the hemicellulosic hydrolysate.

Production of bioethanol from unwashed-pretreated rapeseed straw at high solid loading

Reduction in water consumption and increase in ethanol concentration are two main challenges for bioethanol production from lignocellulosic materials. To address the two challenges, the aim of this work was to study the production of bioethanol from unwashed-pretreated rapeseed straw (RS) at high solid loading. RS pretreated with 1% (w w^-1) H₂SO₄ at 160 °C for 10 min resulted in excellent digestibility and fermentability of pretreated RS. The unwashed-pretreated RS was subjected to presaccharification and fed-batch simultaneous saccharification and fermentation (P-FB-SSF) at a final solid loading of 22% (w w^-1). Ethanol concentration and ethanol yield of 53.1 g L^-1 (equivalent to 4.1% (w w^-1) based on fermentation slurry) and 72.4% were obtained, respectively. In total, 92.1 g water g^-1 ethanol was consumed, a much smaller amount than that observed with washing after pretreatment or fermentation performed at lower solid loading.

Identification of genes involved in xylose metabolism of Meyerozyma guilliermondii and their genetic engineering for increased xylitol production

Meyerozyma guilliermondii, a non-conventional yeast that naturally assimilates xylose, is considered as a candidate for biotechnological production of the sugar alternative xylitol. Because the genes of the xylose metabolism were yet unknown, all efforts published so far to increase the xylitol yield of this yeast are limited to fermentation optimization. Hence, this study aimed to genetically engineer this organism for the first time with the objective to increase xylitol production. Therefore, the previously uncharacterized genes of M. guilliermondii ATCC 6260 encoding for xylose reductase (XR) and xylitol dehydrogenase (XDH) were identified by pathway investigations and sequence similarity analysis. Cloning and overexpression of the putative XR as well as knockout of the putative XDH genes generated strains with about threefold increased xylitol yield. Strains that combined both genetic modifications displayed fivefold increase in overall xylitol yield. Enzymatic activity assays with lysates of XR overexpressing and XDH knockout strains underlined the presumed functions of the respective genes. Furthermore, growth evaluation of the engineered strains on xylose as sole carbon source provides insights into xylose metabolism and its utilization for cell growth.

Anionic structural effect on the dissolution of arabinoxylan-rich hemicellulose in 1-butyl-3-methylimidazolium carboxylate-based ionic liquids

The exploration of a highly efficient and environment-friendly solvent for dissolving hemicellulose is significant. In this study, 1-butyl-3-methylimidazolium carboxylate ([Bmim]carboxylate)-based ionic liquids (ILs), including [Bmim]formate, [Bmim]acetate, [Bmim]propionate, and [Bmim]butyrate, were used as solvents to dissolve arabinoxylan-rich hemicellulose from bamboo. The hemicellulose solubility in the ILs was determined as a function of temperature. The interaction between the hemicellulose and the ILs was evaluated by using ¹H and ¹³C NMR techniques. The hemicelluloses regenerated from the saturated IL solutions were characterized. Results showed that the temperature and structure of carboxylate anions deeply affected the hemicellulose solubility. The carboxylate anion played a more important role than the imidazolium cation in hemicellulose dissolution. The hydrogen bond that formed between the ILs and the hydroxyl groups at the XC2 position of xylopyranose units of hemicellulose was stronger than that between the ILs and the hydroxyl groups at XC3 position of xylopyranose units. The hydrogen bond strength between the hemicellulose and the ILs was affected by the alkyl chain of the carboxylate anion and the hemicellulose concentration. The disruption of the inter- and intra-molecular hydrogen bonds in hemicellulose by the ILs was responsible for the hemicellulose dissolution. The main chain of hemicellulose remained nearly unchanged during the dissolution process.

The exploration of a highly efficient and environment-friendly solvent for dissolving hemicellulose is significant.

Site-Specific Profiling of the Dental Mycobiome Reveals Strong Taxonomic Shifts during Progression of Early-Childhood Caries

Dental caries is one of the most common diseases worldwide. Bacteria and fungi are both commensals in the oral cavity; however, most research regarding caries has focused on bacterial impacts. The oral fungal mycobiome associated with caries is not well characterized, and its role in disease is unclear. ITS1 amplicon sequencing was used to generate taxonomic profiles from site-specific supragingival plaque samples (n = 82) obtained from 33 children with different caries status. Children were either caries free (CF), caries active with enamel lesions (CAE), or caries active with dentin lesions (CA). Plaque samples were collected from caries-free surfaces (PF) and from enamel (PE) and dentin (PD) lesions. Taxonomic profiles representing the different categorizations (CF-PF, CAE-PF, CAE-PE, CA-PF, CA-PE, and CA-PD) were used to characterize the mycobiome and its change through disease progression. A total of 139 fungal species were identified. Candida albicans was the most abundant species, followed by Candida dubliniensis We found that severely progressed plaque communities (CA-PD) were significantly different from healthy plaque communities (CF-PF). A total of 32 taxa were differentially abundant across the plaque categories. C. albicans, C. dubliniensis, Nigrospora oryzae, and an unclassified Microdochium sp. were correlated with caries, whereas 12 other taxa were correlated with health. C. dubliniensis increased steadily as caries progressed, suggesting that C. dubliniensis may play an important role in caries pathogenicity. In contrast, four health-associated fungal taxa have the potential to antagonize the cariogen Streptococcus mutans via xylitol production, suggesting a possible fungal mechanism that could contribute to maintenance of dental health.IMPORTANCE Early-childhood caries is one of the most prevalent diseases in children worldwide and, while preventable, remains a global public health concern. Untreated cavities are painful and expensive and can lead to tooth loss and a lower quality of life. Caries are driven by acid production via microbial fermentation of dietary carbohydrates, resulting in enamel erosion. While caries is a well-studied disease, most research has focused on bacterial impacts, even though fungi are commensal organisms living within the plaque biofilm. There is very little known about how fungi impact caries pathogenicity. The elucidation of fungal taxa involved in caries disease progression is necessary for a more holistic view of the human oral microbiome. Data from this study will improve our understanding of how the fungal community changes as disease progresses and provide insight into the complex etiology of dental caries, which is necessary for the development of treatment plans and preventative measures.

Characterisation of a catalytic triad and reaction selectivity in the dual mechanism of the catalyse hydride transfer in xylitol phosphate dehydrogenase

Xylitol is a high-value low-calorie sweetener used as sugar substitute in food and pharmaceutical industry. Xylitol phosphate dehydrogenase (XPDH) catalyses the conversion of d-xylulose 5-phosphate (XU5P) and d-ribulose 5-phosphate (RU5P) to xylitol and ribitol respectively in the presence of nicotinamide adenine dinucleotide hydride (NADH). Although these enzymes have been shown to produce xylitol and ribitol, there is an incomplete understanding of the mechanism of the catalytic events of these reactions and the detailed mechanism has yet to be elucidated. The main goal of this work is to analyse the conformational changes of XPDH-bound ligands such as zinc^, NADH, XU5P, and RU5P to elucidate the key amino acids involved in the substrate binding. In silico modelling, comparative molecular dynamics simulations, interaction analysis and conformational study were carried out on three XPDH enzymes of the Medium-chain dehydrogenase (MDR) family in order to elucidate the atomistic details of conformational transition, especially on the open and closed state of XPDH. The analysis also revealed the possible mechanism of substrate specificity that are responsible in the catalyse hydride transfer are the residues His58 and Ser39 which would act as the proton donor for reduction of XU5P and RU5P respectively. The structural comparison and MD simulations displayed a significant difference in the conformational dynamics of the catalytic and coenzyme loops between Apo and XPDH-complexes and highlight the contribution of newly found triad residues. This study would assist future mutagenesis study and enzyme modification work to increase the catalysis efficiency of xylitol production in the industry.

Combination of the CRP mutation and ptsG deletion in Escherichia coli to efficiently synthesize xylitol from corncob hydrolysates

The biotechnology-based production of xylitol has received widespread attention because it can use cheap and renewable lignocellulose as a raw material, thereby decreasing costs and pollution. The simultaneous use of various sugars in lignocellulose hydrolysates is a primary prerequisite for efficient xylitol production. In this study, a ΔptsG and crp* combinatorial strategy was used to generate Escherichia coli W3110 strain IS5-dI, which completely eliminated glucose repression and simultaneously used glucose and xylose. This strain produced 164 g/L xylitol from detoxified corncob hydrolysates during a fed-batch fermentation in a 15-L bioreactor, which was 14.7% higher than the xylitol produced by the starting strain, IS5-d (143 g/L), and the xylitol productivity was 3.04 g/L/h. These results represent the highest xylitol concentration and productivity reported to date for bacteria and hemicellulosic sugars. Additionally, strain IS5-dG, which differs from IS5-dI at CRP amino acid residue 127 (I127G), was tolerant to the toxins in corncob hydrolysates. In a fed-batch fermentation experiment involving a 15-L bioreactor, IS5-dG produced 137 g/L xylitol from non-detoxified corncob hydrolysates, with a productivity of 1.76 g/L/h. On the basis of these results, we believe that IS5-dI and IS5-dG may be useful host strains for the industrial-scale production of xylitol from detoxified or non-detoxified corncob hydrolysates.

Improved upstream processing for detoxification and recovery of xylitol produced from corncob

This work deals with the development of an improved process for xylitol production from corn cob hydrolysate by biotechnological routes emphasizing the detoxification of corncob acid hydrolysate. The acid hydrolysate obtained by acid hydrolysis of corn cob was concentrated and detoxified by activated charcoal, membrane process and ion exchange resin process. The resultant partially purified corncob hydrolysate was used in fermentation. The fermentation of acid hydrolysate containing 56.5 g/L xylose was carried out in a 14 L fermenter at pH 4.5 for 48 h with 150 rpm stirring rate at 30 °C. A xylitol yield of 62% was achieved from the partially purified acid hydrolysate medium during fermentation using Candida tropicalis MTCC 6192. The purity of xylitol was increased to 92-94% upon downstream processing of carbonation, subsequently ion exchange process and activated charcoal.

Bioconversion of pentose sugars to value added chemicals and fuels: Recent trends, challenges and possibilities

Most of the crop plants contain about 30% of hemicelluloses comprising D-xylose and D-arabinose. One of the major limitation for the use of pentose sugars is that high purity grade D-xylose and D-arabinose are yet to be produced as commodity chemicals. Research and developmental activities are going on in this direction for their use as platform intermediates through economically viable strategies. During chemical pretreatment of biomass, the pentose sugars were generated in the liquid stream along with other compounds. This contains glucose, proteins, phenolic compounds, minerals and acids other than pentose sugars. Arabinose is present in small amounts, which can be used for the economic production of value added compound, xylitol. The present review discusses the recent trends and developments as well as challenges and opportunities in the utilization of pentose sugars generated from lignocellulosic biomass for the production of value added compounds.

Xylitol production from lignocellulosic whole slurry corn cob by engineered industrial Saccharomyces cerevisiae PE-2

In this work, the industrial Saccharomyces cerevisiae PE-2 strain, presenting innate capacity for xylitol accumulation, was engineered for xylitol production by overexpression of the endogenous GRE3 gene and expression of different xylose reductases from Pichia stipitis. The best-performing GRE3-overexpressing strain was capable to produce 148.5 g/L of xylitol from high xylose-containing media, with a 0.95 g/g yield, and maintained close to maximum theoretical yields (0.89 g/g) when tested in non-detoxified corn cob hydrolysates. Furthermore, a successful integrated strategy was developed for the production of xylitol from whole slurry corn cob in a presaccharification and simultaneous saccharification and fermentation process (15% solid loading and 36 FPU) reaching xylitol yield of 0.93 g/g and a productivity of 0.54 g/L·h. This novel approach results in an intensified valorization of lignocellulosic biomass for xylitol production in a fully integrated process and represents an advance towards a circular economy.

Evaluation of the Simultaneous Production of Xylitol and Ethanol from Sisal Fiber

Recent years have seen an increase in the use of lignocellulosic materials in the development of bioproducts. Because sisal fiber is a low cost raw material and is readily available, this work aimed to evaluate its hemicellulose fraction for the simultaneous production of xylitol and ethanol. The sisal fiber presented a higher hemicellulose content than other frequently-employed biomasses, such as sugarcane bagasse. A pretreatment with dilute acid and low temperatures was conducted in order to obtain the hemicellulose fraction. The highest xylose contents (0.132 g·g-1 of sisal fiber) were obtained at 120 °C with 2.5% (v/v) of sulfuric acid. The yeast Candida tropicalis CCT 1516 was used in the fermentation. In the sisal fiber hemicellulose hydrolysate, the maximum production of xylitol (0.32 g·g-1) and of ethanol (0.27 g·g-1) was achieved in 60 h. Thus, sisal fiber presents as a potential biomass for the production of ethanol and xylitol, creating value with the use of hemicellulosic liquor without detoxification and without the additional steps of alkaline pretreatment.