Xylitol Production Research Articles

Multi-feedstock biorefinery concept: Valorization of winery wastes by engineered yeast

The wine industry produces significant amounts of by-products and residues that are not properly managed, posing an environmental problem. Grape must surplus, vine shoots, and wine lees have the potential to be used as renewable resources for the production of energy and chemicals. Metabolic engineering efforts have established Saccharomyces cerevisiae as an efficient microbial cell factory for biorefineries. Current biorefineries designed for producing multiple products often rely on just one feedstock, but the bioeconomy would clearly benefit if these biorefineries could efficiently convert multiple feedstocks. Moreover, to reduce the environmental impact of fossil fuel consumption and maximize production economics, a biorefinery should be capable to supplement the manufacture of biofuel with the production of high-value products. This study proposes an integrated approach for the valorization of diverse wastes resulting from winemaking processes through the biosynthesis of xylitol and ethanol. Using genetically modified S. cerevisiae strains, the xylose-rich hemicellulosic fraction of hydrothermally pretreated vine shoots was converted into xylitol, and the cellulosic fraction was used to produce bioethanol. In addition, grape must, enriched in sugars, was efficiently used as a low-cost source for yeast propagation. The production of xylitol was optimized, in a Simultaneous Saccharification and Fermentation process configuration, by adjusting the inoculum size and enzyme loading. Furthermore, a yeast strain displaying cellulases in the cell surface was applied for the production of bioethanol from the glucan-rich cellulosic. With the addition of grape must and/or wine lees, high ethanol concentrations were reached, which are crucial for the economic feasibility of distillation. This integrated multi-feedstock valorization provides a synergistic alternative for converting a range of winery wastes and by-products into biofuel and an added-value chemical while decreasing waste released to the environment.

Crystalline xylitol production from corncob biomass with oral toxicity analysis

Xylitol, a five-carbon sugar alcohol, has a steady global market and finds application as a natural sugar substitute in various food and confectionery products. Biocatalytic xylitol production, although touted as a greener alternative to conventional chemical catalysis, suffers from certain challenges, the primary being high cost of production. This study demonstrates a process for food-grade xylitol production from corncob biomass with energy reduction through two major process modifications. A non-conventional fermentation strategy was adopted whereby adjusting aeration without agitation, xylitol with high yield (0.86 ± 0.015 g/g), and productivity (0.74 gL-1h-1) could be produced by a GRAS Pichia caribbica MTCC 5703 strain. Xylitol was recovered from the broth in the form of crystals using a combination of membrane-based filtration and crystallization. The crystals demonstrated ~98 % purity when quantified with 1H NMR. Oral toxicity analysis of the crystals demonstrated no adverse effect in female Winstar rats (at a loading of 2000 mg/kg body weight of animals). Overall process statistics showed that 0.584 kg of food-grade xylitol crystals could be produced from 3.5 kg of corncob biomass. The two-process modifications during fermentation and xylitol recovery enabled an energy saving of ~20.842 kW/kg of crystals, providing tremendous advantages for biorefinery-based large-scale xylitol production from corncob biomass.

RNA-seq based transcriptomic analysis of the non-conventional yeast Spathaspora passalidarum during Melle-boinot cell recycle in xylose-glucose mixtures

The Melle-Boinot is a promising process for second-generation ethanol production by xylose-fermenting yeasts. However, the impact of this process on the physiology of the non-conventional yeast Spathaspora passalidarum during second-generation ethanol production remains unclear. Therefore, we performed a transcriptomic analysis of S. passalidarum to determine the differences and global responses of differentially expressed genes (DEGs) during five fed-batch fermentations with cell recycle. A cycle-to-cycle metabolic reprogramming was observed resulting in an increase in ethanol yield (32%), volumetric productivity (33%), and titer (33%); and an expressive decrease of 94% of xylitol production. A broad set of pathways operated synergically such as fatty acid metabolism, N-glycan biosynthesis, glyoxylate and dicarboxylate metabolism, oxidative phosphorylation, glutathione metabolism and sulfur metabolism, indicating those as important mechanisms for cell recycling adaptations due to increased ethanol concentration, long-term ethanol exposure and osmotic stress. Together these results suggest that cellular energy was redirected towards the production of cell wall components enabling S. passalidarum cells to thrive on consecutive recycles. Furthermore, these results are instrumental to guide genetic-engineering efforts of xylose-fermenting yeasts to improve the productiveness and feasibility of renewable energy production from lignocellulosic biomass and hemicellulosic hydrolysates.

Deep Eutectic Solvent Pretreatment of Water Hyacinth for Improved Holocellulosic Saccharification and Fermentative Co-Production of Xylitol and Lipids Using Rhodosporidium toruloides NCIM 3547

In this study, delignification of water hyacinth (WH) using a mild ionic liquid-like chemical deep eutectic solvent (DES) synthesized using choline chloride and urea was conducted and the process parameters were optimized by Box–Behnken design (BBD)-based response surface methodology (RSM). From the results, a delignification of 64.32 ± 4.08% (w/w) was obtained under 1:12.5 (biomass:DES ratio), 4.63 h (time) and 87 °C (temperature). Further, a dilute sulphuric acid (2%, v/v) hydrolysis was carried out to destabilize the hemicellulose that resulted in 23.7 ± 0.50 g/L of xylose. Fermentation of the obtained xylose was carried out using a red oleaginous yeast, Rhodosporidium toruloides NCIM 3547, with free and Ca2+-alginate-immobilized cells for xylitol production under microaerophilic conditions and obtained yields of 4.73 ± 0.40 g/L (168 h) and 9.18 ± 0.10 g/L (packed bed reactor with a retention time of 18 h), respectively. Further, when the same fermentation was performed under aerobic conditions about 40.93 ± 0.73% lipid accumulation was observed with free cells. For saccharification, Aspergillus-niger-derived cellulase was used and this resulted in a yield of 27.45 ± 0.04 g/L of glucose. The glucose-enriched hydrolysate was supplemented for fermentation under nitrogen starved conditions from which 46.81 ± 2.60% (w/w) lipid content was obtained.

Biological production of xylitol by using nonconventional microbial strains.

Xylitol (C5H12O5), an amorphous sugar alcohol of crystalline texture has received great interest on the global market due to its numerous applications in different industries. In addition to its high anticariogenic and sweetening properties, characteristics such as high solubility, stability and low glycemic index confer xylitol its fame in the food and odontological industries. Moreover, it also serves as a building-block in the production of polymers. As a result of the harmful effects of the chemical production of xylitol, the biotechnological means of producing this polyol have evolved over the decades. In contrast to the high consumption of energy, long periods of purification, specialized equipment and high production cost encountered during its chemical synthesis, the biotechnological production of xylitol offers advantages both to the economy and the environment. Non-Saccharomyces yeast strains, also termed as nonconventional, possess the inherent capacity to utilize D-xylose as a sole carbon source, unlike Saccharomyces species.

Improving glycerol utilization during high-temperature xylitol production with Kluyveromyces marxianus using a transient clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 system

Glycerol is an ideal co-substrate for xylitol production with Kluyveromyces marxianus. This study demonstrated that K. marxianus catabolizes glycerol through the Gut1-Gut2 pathway instead of the previously speculated NADPH-dependent Gcy1-Dak1 pathway using the transient clustered regularly interspaced short palindromic repeats/ CRISPR-associated protein 9 (CRISPR/Cas9) system. Additionally, Utr1p was demonstrated to mediate NADPH generation through NADH phosphorylation. YZB392, which was constructed by integrating Utr1 into the Ypr1 site in the strain overexpressing NcXyl1 and CiGxf1 and harboring disrupted Xyl2, exhibited enhanced glycerol utilization for xylitol production (from 2.50- to 3.30- g/L after consuming 1 g/L glycerol). Fed-batch fermentation at 42 °C with YZB392 yielded 322.07 g/L xylitol, which is the highest known xylitol titer obtained via biological method. Feeding crude glycerol, xylose mother liquor, and corn steep liquor powder into a bioreactor resulted in the production of 235.69 g/L xylitol. This study developed a platform for xylitol production from industrial by-products.

Lignocellulosic xylitol production from corncob using engineered Kluyveromyces marxianus.

Xylitol production from lignocellulose hydrolysate is a sustainable and environment-friendly process. In this study, a systematic process of converting corncob waste into xylitol is described. First, the corncobs are hydrolyzed with acid to a hydrolysate. Second, Kluyveromyces marxianus YZJQ016 derived from K. marxianus YZJ074, constructed by overexpressing ScGAL2-N376F from Saccharomyces cerevisiae, CtXYL1 from Candida tropicalis, and KmZWF1 from K. marxianus, produces xylitol from the hydrolysate. A total of ten xylose reductase genes were evaluated, and CtXYL1 proved best by showing the highest catalytic activity under the control of the KmGAPDH promoter. A 5L fermenter at 42°C produced 105.22g/L xylitol using K. marxianus YZJQ016-the highest production reported to date from corncob hydrolysate. Finally, for crystallization of the xylitol, the best conditions were 50% (v/v) methanol as an antisolvent, at 25°C, with purity and yield of 99%-100% and 74%, respectively-the highest yield reported to date.

Mathematical modeling of the biotechnological production of xylitol from hydrolysates of agro-industrial waste

Xylitol is widely used in the pharmaceutical and food industries since it has cariogenic properties and low caloric value compared to sucrose. In recent decades, its demand has increased, which has motivated the generation of alternatives for its production. The biotechnological route is an attractive alternative since in addition to reducing production costs, it uses lignocellulosic hydrolysates from agro-industrial residues as raw material. However, due to the inherent variability in the composition of the waste, the implementation of the process is not a simple task, i. e., the determination of the operating conditions that maximize production yield requires a broad experimental design. In this sense, mathematical modeling can help reduce experimental work, and allows for predicting and evaluating the dynamic behavior of key variables, making it a useful tool for the implementation of process optimization and control schemes. Therefore, the objective of this work is to propose a generalized mathematical model that can be adapted to different study cases (i.e., different substrates and microorganism strains), operating conditions, and fermenter configuration. The results show high determination coefficients R2 > 0.90 for each case study, indicating that the proposed model is easily adaptable to different substrates and operating conditions. In addition, the model allows the incorporation of different effects such as pH, temperature, and agitation.

An Integrated Process for the Xylitol and Ethanol Production from Oil Palm Empty Fruit Bunch (OPEFB) Using Debaryomyces hansenii and Saccharomyces cerevisiae.

Oil palm empty fruit bunch (OPEFB) is the largest biomass waste from the palm oil industry. The OPEFB has a lignocellulose content of 34.77% cellulose, 22.55% hemicellulose, and 10.58% lignin. Therefore, this material’s hemicellulose and cellulose content have a high potential for xylitol and ethanol production, respectively. This study investigated the integrated microaerobic xylitol production by Debaryomyces hansenii and anaerobic ethanol semi simultaneous saccharification and fermentation (semi-SSF) by Saccharomyces cerevisiae using the same OPEFB material. A maximum xylitol concentration of 2.86 g/L was obtained with a yield of 0.297 g/gxylose. After 96 h of anaerobic fermentation, the maximum ethanol concentration was 6.48 g/L, corresponding to 71.38% of the theoretical ethanol yield. Significant morphological changes occurred in the OPEFB after hydrolysis and xylitol and ethanol fermentation were shown from SEM analysis.

Efficient process for xylitol production from nitric acid pretreated rice straw derived pentosans by Candida tropicalis GS18

Valorization of agricultural residues has garnered worldwide interests due to their inexpensive, renewable and environment friendly nature. Among various lignocellulosic wastes, rice straw is the third-most abundantly available biomass rich in hemicelluloses and an easily accessible biomass for biological production of xylitol. In the present study, dilute nitric acid was employed for fractionation of hemicellulosic component of rice straw. Screening of various parameters such as solid to liquid ratio, acid concentration, residence temperature and time was carried out for maximal liberation of fermentable sugars. Xylose conversion was attained to the extent of 71.32% from the xylan of rice straw upon treating with 1% (v/v) dilute HNO3 at 121 °C for 30 min. In the process, complete removal of furfurals and HMF as well as partial removal of acetic acid was achieved by using 2% (w/v) activated carbon. Maximum xylitol titre of 25.15 g/L and 34.21 g/L was obtained during fermentation of non-detoxified and detoxified hydrolysate of rice straw biomass respectively by the newly isolated strain of Candida tropicalis GS18 at 30 °C, 150 rpm and pH 5.5 after 96 h of fermentation. This study suggested the use of dilute nitric acid as an effective and environment friendly catalyst for efficient recovery of xylose from rice straw and its subsequent use for xylitol production.

Fermentation process optimisation based on ANN and RSM for xylitol production from areca nut husk followed by xylitol crystal characterisation

Areca nut husk is an agricultural bio-waste with massive potential for producing value-added chemicals by conversion of xylose present in it through fermentation. This study aimed to optimise the production of xylitol from areca nut husk hemicellulosic acid hydrolysate (as the substrate) by using Candida tropicalis (MTCC 6192). Response Surface Methodology (RSM) and Artificial Neural Network (ANN) were compared for fermentation process optimisation in modelling and prediction. Agitation, pH, temperature, xylose concentration and operation time were considered variable parameters. The maximum concentration of xylitol obtained was around 9.96 g/L under designed conditions. Crystallisation analysis was conducted to separate pure xylitol crystal from fermented broth, followed by characterisation of xylitol crystal such as X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Thermogravimetric Analysis (TGA), Differential scanning calorimetry (DSC) and Raman analysis. DSC analysis revealed that the melting process of commercial xylitol crystals after crystallisation (CXCAC) was observed at 93.71 °C with enthalpies of 210.7 J/g. However, almost similar results were observed for xylitol crystals from fermentation broth (XCFB), with a melting point at 91.73 °C and enthalpies of 220 J/g.

Techno-Economic Analysis of an Integrated Bio-Refinery for the Production of Biofuels and Value-Added Chemicals from Oil Palm Empty Fruit Bunches

Lignocellulose-rich empty fruit bunches (EFBs) have high potential as feedstock for second-generation biofuel and biochemical production without compromising food security. Nevertheless, the major challenge of valorizing lignocellulose-rich EFB is its high pretreatment cost. In this study, the preliminary techno-economic feasibility of expanding an existing pellet production plant into an integrated bio-refinery plant to produce xylitol and bioethanol was investigated as a strategy to diversify the high production cost and leverage the high selling price of biofuel and biochemicals. The EFB feedstock was split into a pellet production stream and a xylitol and bioethanol production stream. Different economic performance metrics were used to compare the profitability at different splitting ratios of xylitol and bioethanol to pellet production. The analysis showed that an EFB splitting ratio below 40% for pellet production was economically feasible. A sensitivity analysis showed that xylitol price had the most significant impact on the economic performance metrics. Another case study on the coproduction of pellet and xylitol versus that of pellet and bioethanol concluded that cellulosic bioethanol production is yet to be market-ready, requiring a minimum selling price above the current market price to be feasible at 16% of the minimum acceptable return rate.

Integrated and partial process of xylitol and bioethanol production from oil palm empty fruit bunches

Oil palm empty fruit bunches (OPEFBs) are highly abundant in Indonesia and have been highlighted as a potential feedstock for bioethanol and xylitol production. However, the efficacy of the fermentation technology to convert OPEFBs to bioethanol and xylitol, either in partial (i.e. mono-production) or integrated (i.e. co-production) process, still needs further improvement. This study aimed to evaluate the partial and integrated process for xylitol and bioethanol production from OPEFBs. In the integrated process, the remaining solid residues after xylitol extraction are used as feedstock for bioethanol due to their high cellulose compounds. This solid residue is more susceptible to be degraded by cellulase enzymes into glucose and further transformed into bioethanol. In the partial process of xylitol production, xylanase enzyme was used to hydrolyze xylan into xylose, which was then converted into xylitol using Debaryomyces hansenii. While in the partial process of bioethanol production, the hydrolysis of cellulose in the OPEFB into glucose was carried out using cellulase enzymes, followed by fermentation using Saccharomyces cerevisiae. The results show that the partial process produced xylitol yield (Yp/s) of 0.10 g-xylitol/g-xylose, while bioethanol at yield (Yp/s) of 0.32 g-bioethanol/g-glucose, respectively. The integrated process generates xylitol yield (Yp/s)of 0.298 g-xylitol/g-xylose, with bioethanol yield from the remaining solid at 0.051 g-bioethanol/g-OPEFB (or 0.078 g-bioethanol/g-glucose). These findings, therefore, confirmed that the integrated process of xylitol with bioethanol production might offer higher efficacy of OPEFB utilization into high value-added products.

Sugarcane Bagasse-Based Ethanol Production and Utilization of Its Vinasse for Xylitol Production as an Approach in Integrated Biorefinery

Biorefinery of sugarcane bagasse into ethanol and xylitol was investigated in this study. Ethanol fermentation of sugarcane bagasse hydrolysate was carried out by Saccharomyces cerevisiae. After ethanol distillation, the vinasse containing xylose was used to produce xylitol through fermentation by Candida guilliermondii TISTR 5068. During the ethanol fermentation, it was not necessary to supplement a nitrogen source to the hydrolysate. Approximately 50 g/L of bioethanol was produced after 36 h of fermentation. The vinasse was successfully used to produce xylitol. Supplementing the vinasse with 1 g/L of yeast extract improved xylitol production 1.4-fold. Cultivating the yeast with 10% controlled dissolved oxygen resulted in the best xylitol production and yields of 10.2 ± 1.12 g/L and 0.74 ± 0.04 g/g after 60 h fermentation. Supplementing the vinasse with low fraction of molasses to improve xylitol production did not yield a positive result. The supplementation caused decreases of up to 34% in xylitol production rate, 24% in concentration, and 24% in yield.

An appropriate unstructured kinetic model describing the batch fermentation growth of Debaryomyces hansenii for xylitol production using hydrolysis of oil palm empty fruit bunch

This study aimed to determine an appropriate unstructured kinetic model describing the growth of Debaryomyces hansenii with the hydrolysis of oil palm empty bunches as the substrate sources. We tested the well-known cell growth kinetic models for approximating the xylitol fermentation data. We modeled the extracellular process by considering the biomass as a variable, xylose as the substrate and xylitol as the product. The appropriate kinetic model was determined by fitting the models to the experimental data. The fitting process involved an optimization procedure that minimizes a least-squared error between the model solution and the experimental data using a gradient-based method. We found that the unstructured model with Monod specific kinetic growth model had the best approximating ability to describe the dynamics of the batch xylitol fermentation data. Some factors were highlighted as the key factors that influence the growth of yeast cells. One of them is the maximum growth rate of the yeast cell which had a high sensitivity to the maximum production of new cells and xylitol as the main product. As Monod was the best-approximated model, it implies that inhibitory effects by substrate and product played an important role in controlling the growth of yeast cells. There was a certain maximum growth rate for the yeast cell that generates maximum production of new cells and xylitol within a relatively short fermentation time. This result indicates that the growth rate parameter played an important role in adjusting the fermentation process for optimality purposes.

Kinetic study and model of fermentation parameters affected growth and xylitol production in bioreactor by Kluyveromyces marxianus ATCC 36,907

Kinetic study and model of fermentation parameters affected growth and xylitol production in bioreactor by Kluyveromyces marxianus ATCC 36,907

Xylitol Production from Corncob Hydrolysate by an Engineered Escherichia coli M15 as Whole-Cell Biocatalysts

Xylitol Production from Corncob Hydrolysate by an Engineered Escherichia coli M15 as Whole-Cell Biocatalysts

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 gethanol/gglucose and 0.344 gethanol/gcellobiose, 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 gethanol/gGX and 0. 380 gethanol/gGXC, respectively. Likewise, in identical conditions, C. lusitaniae produced xylitol from xylose with a yield of 0.421 gxylitol/gxylose. 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.

Xylitol production from rice straw hemicellulosic hydrolysate by Candida tropicalis GS18 immobilized on bacterial cellulose-sodium alginate matrix

Xylitol production from rice straw hemicellulosic hydrolysate by Candida tropicalis GS18 immobilized on bacterial cellulose-sodium alginate matrix

Exploitation of plant-derived food waste for valuable products using bioprocesses: a narrative review

Globally, a million tons of plant-derived food waste are generated annually from various cultivation activities and agro-industrial manufacturing. When food waste decomposes, it releases methane gas that causes global warming. The exploitation of food wastes for valuable products provides an alternative approach to environmental protection. This paper aimed to review the exploitation of plant-derived food waste for valuable products and to evaluate different bioprocesses for optimum yields of the valuable products. This review study was conducted by using PubMed, ScienceDirect, and NCBI databases. A total of 169 publications were screened and 43 papers of high relevance were selected. Cereal wastes such as wheat straw, rice bran, root and tuber waste, and fruits and vegetable pomace contribute the most amounts to the total food waste worldwide. These wastes serve as renewable sources for bioactive production. Various fermentation processes involving enzymes, yeast, or bacteria were used to convert food waste into valuable products such as phenolics, flavonoids, dietary fibre, carotenoids, lignocellulose, phytosterols, tocotrienols, coumaric acid, oryzanol, citrulline, vitamins, and essential amino acids. Several bioprocesses and the optimization conditions for the maximum yield of valuable products were highlighted. In the production of xylitol from corn cobs using yeast (Debaryomyces hansenii), a higher yield (0.216 g xylitol/g xylose) was obtained through enzyme hydrolysate fermentation compared to acid hydrolysate fermentation (0.100 g xylitol/g xylose). In the production of fungal chitosan using solid-state fermentation, the yield was 3 folds higher (34.4 g/kg substrate) for soybean meals substrate than potato peels substrate (10.8 g/kg substrate). Plant-derived food waste serves as a renewable substrate for the production of health-promoting bioactive compounds through the optimization of various bioprocesses. The exploitation of plant-derived food waste for high-value products has significant implications for environmental impact, public health, and economic gain.