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Xylitol is a sugar alcohol that is used as a sweetener for diabetics and also for other purposes (e.g., in chewing gum). Industrially, xylitol is manufactured through a chemical process that has some disadvantages, including a high energy requirement, extensive purification steps, and a high cost of product. The microbial production of xylitol has...
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... of xylitol by yeast. A scheme diagram of xylose metabolism in microorgan- isms is shown in Fig. 2. Xylitol is produced as a metabolic intermediate compound in all organisms whose xylose metabolism takes place in a sequential activity of XR and XDH enzymes (Fig. 2). Keeping this in view, various researchers have been engaged in microbial screening studies to identify efficient strains for the production of xylitol. Several wild-type ...
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... of xylitol by yeast. A scheme diagram of xylose metabolism in microorgan- isms is shown in Fig. 2. Xylitol is produced as a metabolic intermediate compound in all organisms whose xylose metabolism takes place in a sequential activity of XR and XDH enzymes (Fig. 2). Keeping this in view, various researchers have been engaged in microbial screening studies to identify efficient strains for the production of xylitol. Several wild-type and recombinant yeasts have been used for the fermentative produc- tion of xylitol (Table 1). Biological production of xylitol by yeasts has been reported, (27) ...
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... NADP + -or NAD + -linked xylitol dehydrogenase (XDH). These two reactions are selected as the rate-limiting steps for xylose metabolism and xylitol produc- tion. Xylulokinase (EC 2.7.1.17) catalyzes the phosphorylation of xylulose to xylulose 5-phosphate (X5P) and subsequently the resulting product can enter the pentose phos- phate pathway (PPP) (Fig. 2) 6-phosphate) are oxidized to pentose phosphates (such as ribulose 5-phosphate), provid- ing the NADPH needed in biosynthetic pathways. In the nonoxidative phase, pentose phosphates are transformed to hexose and triose phosphates. Fructose 6-phosphate and glyceraldehyde 3-phosphate are produced from X5P in the nonoxidative phase of the ...
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... of histidine and nucleic acids). In the fermen- tative route, pyruvate decarboxylase converts pyruvate into acetaldehyde and, subsequently, alcohol dehydrogenase acts on the acetaldehyde to yield ethanol. Alternatively, in the oxi- dation path, pyruvate is oxidized in the TCA cycle and the respiratory chain while there is available oxygen (Fig. 2). The transformation of X5P into acetyl phosphate and glycer- aldehyde 3-phosphate by xylulose 5-phosphate phosphoketolase represents an alternative pathway for its use. (1,139) The ratio of XR and XDH and the coenzyme-regenerating system are the main metabolic regulators to produce xylitol. (53) A higher ratio of XR to XDH activity is ...
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... to XDH activity is required to accumulate xylitol. XR and XDH are the crucial enzymes in xylitol biosynthesis by yeasts. These two enzymes need pyridine nucleotide coenzymes showing specificity towards its different forms (NADH or NADPH) in different yeasts. Under aerobic con- ditions, the NADH formed in the second step of the xylose metabolism (Fig. 2) can be reoxidized in the electron transport system, and as a consequence, xylitol is not produced. (10) Under oxygen-limited or anaerobic conditions, a redox imbalance occurs due to a variation in the coenzyme necessity of these enzymes that leads yeasts to accumulate xylitol. Oxygen-limited conditions favor xylitol synthesis because ...
Citations
... Thus, pretreatment operations intend to break down hemicelluloses and remove the resulting isolated products but leave cellulose and lignin partially, if not entirely, intact. The extracted products of the hemicellulose fractionation are contained mainly in an aqueous byproduct and can serve to produce, for example, specialty chemicals [16][17][18][19][20][21][22], while the remaining cellulose-rich product (i.e., a solid fraction) can be utilized for biofuels production after a hydrolysis step. Processes such as hot water extraction (HWE) or autohydrolysis (in the presence of water only) are possible pathways toward this goal [14]. ...
... [21] Xylose for xylitol production Xylitol from xylose using enzyme technology as an alternative to both chemical and microbial processes; biological conversion of xylose and uses of xylitol; catalytic routes for xylose conversion to value-added chemicals; challenges to produce bioproducts based on xylose. [16,18,44] Furfural and HMF using water-based pretreatment process ...
... HTL of sewage sludge (at 325 • C for 30 min) resulted in an aqueous phase constituted by: TS:16.53 ± 0.94 g/L, VS: 15.18 ± 0.73 g/L, COD: 19.30 ± 0.90 g/L, TOC:4.44 ± 0.44 g/L, TN: 3.04 ± 2.52 g/L, phenolic compounds 2654.11 ± 98.71 mg/L, acetate 1531.86 ± 66.37 mg/L, propionate 748.03 ± 36.38 mg/L, butyrate 125.39 ± 8.07 mg/L, Na: 59.23 ± 1.62 mg/L, ammonium 1993.71 ...
Thermochemical pretreatments are employed prior to energy, chemicals, and fuels production from biomass. Wet thermochemical processes (WTCP) are treatments used to modify biomass properties in water as the primary solvent, with or without added reactants/catalysts. WTCP includes hot water extraction, steam explosion, hydrothermal liquefaction, hydrothermal carbonization (HTC), and supercritical water gasification. WTCP also includes processes that add chemicals to reduce reaction time and improve efficiency, i.e., organosolv, alkali, and low acid pretreatment. Operational parameters in WTCP are usually selected to optimize the yields of sugars after enzymatic hydrolysis of the resulting solids and biogas from the pretreated solids, or to ensure that hydrochar (e.g., from HTC) performs adequately in environmental applications. However, a key byproduct from WTCPs is an aqueous fraction (rich in nutrients, hemicellulose-derived sugars, and chemicals) often disposed of as waste. The necessity of resource conservation and proper management and the need to make WTCP-based biorefineries economically and environmentally sound require using all the byproducts of biomass processing. Options for downstream conversion of the WTCPs' aqueous byproducts are dispersed in the literature. Thus, this paper aims to put together works that report the parameters of WTCPs that allowed removing hemicellulose-derived fractions and nutrients from biomass (either partially or almost entirely), the yields and properties of this aqueous byproduct, methods of characterization, current and expected uses, and the challenges for scaling up WTCPs and using the aqueous stream. The paper focuses on expected and existing methods that allow the valorization of the aqueous fraction and reduce wastes within a circular bioeconomy framework.
... Compared to other hydrolysis methods, acid hydrolysis excels at converting xylan into xylose due to its rapid hydrolysis rate, high reactivity and solubility of carbohydrates, and high delignification . This makes xylose the most abundant sugar released in the hydrolysate (Rafiqul and Mimi Sakinah, 2013). ...
The progression of sustainable practices in biorefineries is pivotal in mitigating carbon emissions and optimizing the utilization of natural resources, thereby preserving the environment. Biorefineries, which convert lignocellulosic biomass into a variety of products, distinguish themselves by efficiently transforming waste into high-value products. Xylitol stands out among biorefinery products. Derived from the conversion of xylose present in lignocellulose, it not only offers health benefits but is also considered an intermediate molecule in the production of valuable chemical products. Microbiological methods for xylitol production are increasingly acknowledged as efficient and environmentally friendly alternatives. These are some of the main factors discussed in this review, which aims to demonstrate the biotechnological route for producing xylitol through lignocellulosic materials. Several studies were observed to characterize various lignocellulosic residues, and it was noted that Eucalyptus globulusand banana leaves exhibit high levels of xylose. By analyzing the most recent researches related to xylitol production, the possibility of co-production of bioethanol using the same biotechnological route of xylitol production was identified. For instance, studies have shown that a combination of bagasse and sugarcane straw, as well as rice straw residue, are capable of producing substantial levels of xylitol and ethanol. The yields reached 30.61 g/L of xylitol and 47.97 g/L of ethanol, and 34.21 g/L of xylitol and 2.12 g/L of ethanol, respectively. These innovations not only promote sustainability but also have the potential to generate positive impacts on the global economy.
... Xylitol has a similar flavor and sweetness as sucrose, and it is recommended to be consumed by diabetic patients since the metabolism does not require insulin. It has also been proven that xylitol is able to prevent tooth decay, thus it has been incorporated into some healthcare products such as toothpaste, and mouthwash (Rafiqul & Sakinah, 2013). Therefore, xylitol can be regarded as a dental friendly non-fermentable sugar alcohol. ...
... Xylitol can also be produced through microbial and enzymatic methods. The microbial process utilizes bacteria, yeast, or fungi to produce xylitol from xylose or hemicellulosic hydrolyzate (Rafiqul & Sakinah, 2013). Xylitol is produced as an intermediate product in the metabolic pathway of xylose. ...
Sugar is commonly used on a daily basis but, consuming excessive sugar can lead to various health issues such as diabetes, cardiovascular, and respiratory illnesses. As a result, the food industry has been manufacturing artificial sweeteners in order to reduce the risk of disease development. This research aims to compare the roles of xylitol and sorbitol based on their chemical value, as well as the benefits and drawbacks of their use in food applications. Sugar alcohols are mostly employed as thickeners and sweeteners and are additionally referred to as bulk sweeteners. Xylitol is typically found in fruits, vegetables, and hardwood trees. Furthermore, when compared to sucrose, xylitol includes similar tastes and sweeteners, though insulin is not required during metabolism. Additionally, it is used in healthcare products such as toothpaste and mouthwash due to its ability to prevent tooth decay. Similarly, sorbitol can be found in fruits and vegetables and is frequently employed as a sweetener, texture enhancer, and moisture maintainer. Nevertheless, xylitol and sorbitol may have their own set of advantages and disadvantages. It has been found that xylitol has a wide range of potential health benefits, including lower blood glucose and insulin response, and less sweetness intensity than sucrose. However, a drawback of ingesting xylitol is that it provides low-GI energy, making it unsuitable for people with low glucose levels, and it has a lower laxation threshold. Sorbitol also provides health benefits as it supplies calories and has a low glycemic index.
... Other desirable products of acid hydrolysis include amino acids, which are used in the production of food additives, and fatty acids, which are used in the manufacture of soaps and detergents (Naik et al., 2010). The yield of the soluble fraction depends on the type of biomass and the reaction conditions (Abril and Navarro, 2012;Hyvönen et al., 1982;Rafiqul and Sakinah, 2013;Yi and Zhang, 2012). The branched and amorphous arrangement of hemicellulose allows it to be readily hydrolyzed, with a recovery of 70-95% of its sugars. ...
... The temperature is controlled in the range of 140-200°C as it considerably influences the product selectivity and regulates the overall reaction kinetics. Together with the increase in temperature, the high pressure (around 5 Mpa) favors the hydrogen solubility and the achievement of a high hydrogenation velocity in bulk liquid (Rafiqul and Sakinah, 2013;Su et al., 2013). The kinetic model of the reaction is semi-competitive, with the pentose sugar occupying the catalytic active site. ...
... It utilizes the Entner-Doudoroff pathway to synthesize bioethanol closer to the maximum theoretical yield under anaerobic conditions [19]. Several Candida species can assimilate and reduce xylose to xylitol [20]. Amid xylitol synthesizing yeasts, C. tropicalis is usually employed for effective xylitol biosynthesis via NADPH-dependent xylose reductase enzyme for more adaptable oxidoreduction regeneration [12,21]. ...
Co-generation of high value-added products like xylitol, which has various applications in the pharmaceutical and food industries, can support the economics of bioethanol in an integrated biorefinery. This work proposes a sequential fermentation approach using Z. mobilis and C. tropicalis to produce bioethanol and xylitol from mixed sugars (glucose and xylose) in a single bioreactor. The sequential fermentation without ethanol separation resulted in lower xylose uptake due to the repressive effect of ethanol on C. tropicalis. Thus, an in situ distillation technique was employed for bioethanol recovery prior to xylose fermentation by C. tropicalis. From the mixture of glucose and xylose (60 and 50 g/L), the ethanol and xylitol concentration of 29.94 ± 0.208 g/L and 35.15 ± 0.472 g/L with fermentation efficiency of 97.14 ± 1.054% and 78.55 ± 0.304% respectively was achieved. Fed-batch configuration was further incorporated into this strategy to enhance the xylitol production, which resulted in the high xylitol concentration, productivity, and yield of 86.76 ± 0.416 g/L, 2.07 ± 0.010 g/L/h, and 0.87 ± 0.004 g/g respectively. The bioethanol and xylitol titer, productivity, and yield obtained from sequential fermentation of mixed sugars were similar to the distinct glucose and xylose fermentation in a bioreactor. The proposed technique can be a promising approach for developing lignocellulosic material-based biorefineries to produce bioethanol and xylitol economically and sustainably.
Graphical Abstract
... The production of xylitol by extraction from its natural sources is impractical and uneconomical due to the relatively small quantities in which it occurs, therefore it is customary to obtain it either by synthesis or using biotechnological processes. Among microorganisms, yeast are the best producers of xylitol, especially those belonging to the genus Candida [212][213][214][215]. ...
The origins of primitive living organisms trace back to the enigmatic environment of seawater. While the exact processes leading to the emergence of life remain shrouded in mystery, numerous hypotheses have been put forth, albeit with varying degrees of supporting evidence. This book seeks to shed light on the fascinating journey of protomembranes and their transformation into bilayer lipid membranes from inert substances. The emergence of complex lipids, particularly polyols, played a crucial role in this process, potentially marking the birth of biological membranes and life on Earth as we know it.
One prevailing model used to explain the formation of protomembranes is the coacervates from the Oparin-Haldane hypothesis. These protomembranes, initially consisting of fatty acids and other amphiphiles, represented a simpler form of membranes. However, with the introduction of polyols and the subsequent formation of complex lipids, a new type of protomembrane emerged. This suggests that the inclusion of complex lipids, facilitated by polyols, may have set the stage for the eventual development of biological membranes and the emergence of life.
In exploring the chemical and mathematical models, we gain further insights into the composition and transformation of protomembranes. The chemical model delves into the spontaneous formation of polyols within the primordial broth, shedding light on the specific polyols that could have been present. Additionally, the mathematical model reveals that ethylene glycol, glycerol, and butane-1,2,3,4-tetraols accounted for approximately 90% of all polyols produced. This indicates a potential prevalence of diol lipids in the primitive protomembranes.
Through the course of chemical evolution, as environmental conditions such as temperature, pH, and other factors fluctuated, diol lipids gradually gave way to glycerolipids. The latter displayed more favorable physicochemical characteristics that proved instrumental in the formation of biological membranes across diverse organisms. The book elucidates the presence of polyols as integral components of complex lipids found in modern biological membranes, emphasizing their significance in the evolution and function of life.
By expanding our understanding of polyols and their role in complex lipid synthesis, this book serves as a gateway to new discoveries and deeper insights into the origins and development of biological membranes. By delving into the intricate interplay of chemistry, mathematics, and evolution, we embark on a captivating journey that uncovers the fundamental building blocks of life on Earth.
... As shown in Figure 2B, raffinose and dulcitol exhibited opposite accumulation trends with increasing leaf maturity; raffinose showed the highest level in the 4th leaf, and dulcitol showed the highest level in the bud. Xylitol is a pentose alcohol that is an ideal sweetener for patients with diabetes (23). In fresh tea leaves, the highest level of xylitol was observed in the 4th leaf ( Figure 2B, Profile 41). ...
Background
Jianghua Kucha (JHKC) is a special tea germplasm with enriched specialized secondary metabolites, including theacrine, non-epimeric flavanols and methylated flavanols. Moreover, primary metabolites provide precursors and energy for the production of secondary metabolites. However, the accumulation patterns of primary and secondary metabolites in different tissues of JHKC are unclear.
Methods
The changes of primary and secondary metabolites and related metabolic pathways (primary and secondary metabolism) in different JHKC tissues (the bud, 1st-4th leaves, and new stem) were investigated via metabolomics analysis with ultra-high-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UHPLC-QTOF/MS).
Results
Significant differences were observed in 68 primary and 51 secondary metabolites mainly related with the pathways of starch and sucrose, amino acids, caffeine, and flavanols metabolism and TCA cycle. The bud exhibited higher levels of glucose-6-phosphate, citric acid, most amino acids, theobromine, catechin-gallate, epicatechin-gallate, procyanidins, and theasinensins; the 1st leaf showed higher levels of caffeine and epigallocatechin-3-gallate; and the 4th leaf contained higher levels of most monosaccharides, theacrine, and epigallocatechin-3-O-(3”-O-methyl)-gallate. In addition, primary metabolites and important secondary metabolites had certain correlations.
Conclusion
This study provides comprehensive insight into primary and secondary metabolites in JHKC and offers guidelines for efficiently utilizing specialized metabolites of JHKC in the future.
... Moreover, hemicellulose-active redox enzymes may be used to increase the value of pentose sugars by converting them to alditols (such as xylitol and arabinitol, two among the top twelve value-added chemicals from biomass [93]) or aldonic acids (such as xylonic acid [49,50,160,161]). Both sugar alcohols and sugar acids can be produced by chemical, microbial, or enzymatic (using specific sugar dehydrogenases) reduction [48] or oxidation [162], respectively. However, reduction of pentose sugars, such as xylose to xylitol, is currently done chemically at industrial scale, one example being DuPont's trademark process producing XIVIA Xylitol from xylose remaining after pulp cooking of corn stover [106]. ...
Lignocellulosic biomass is the most abundant source of carbon-based material on a global basis, serving as a raw material for cellulosic fibers, hemicellulosic polymers, platform sugars, and lignin resins or monomers. In nature, the various components of lignocellulose (primarily cellulose, hemicellulose, and lignin) are decomposed by saprophytic fungi and bacteria utilizing specialized enzymes. Enzymes are specific catalysts and can, in many cases, be produced on-site at lignocellulose biorefineries. In addition to reducing the use of often less environmentally friendly chemical processes, the application of such enzymes in lignocellulose processing to obtain a range of specialty products can maximize the use of the feedstock and valorize many of the traditionally underutilized components of lignocellulose, while increasing the economic viability of the biorefinery. While cellulose has a rich history of use in the pulp and paper industries, the hemicellulosic fraction of lignocellulose remains relatively underutilized in modern biorefineries, among other reasons due to the heterogeneous chemical structure of hemicellulose polysaccharides, the composition of which varies significantly according to the feedstock and the choice of pretreatment method and extraction solvent. This paper reviews the potential of hemicellulose in lignocellulose processing with focus on what can be achieved using enzymatic means. In particular, we discuss the various enzyme activities required for complete depolymerization of the primary hemicellulose types found in plant cell walls and for the upgrading of hemicellulosic polymers, oligosaccharides, and pentose sugars derived from hemicellulose depolymerization into a broad spectrum of value-added products.
... Xylitol production is based mainly on chemical and enzymatic processes (Rafiqul and Sakinah, 2013). However, each process has its advantages and disadvantages. ...
... The Km, app. For xylose and NADPH were given by Rafiqul and Mimi Sakinah (2012) and Rafiqul and Sakinah (2013). Already, XR isolated from the filamentous fungus Thermomyces lanuginosus presented values of Km and Vmax, using xylose as a substrate, of 15.36mM and 88.61 (pmol/mg/min), respectively, and for the NADPH cofactor, the values of Km and Vmax were 30.44mM and 94.43 ± 2.24 (pmol/mg/min), respectively (Zhang et al., 2019). ...
In 1891, a German chemist by the name of Emil Fischer, winner of the Nobel Prize in Chemistry in 1902, was the first to actually obtain xylitol using chemical methods and as a source ofbiomass, wood (D-xylose) (O’Donnell and Kearsley, 2012). In the 1930s, inter¬est in commercializing xylitol as a sweetener began because of a shortage of sugar during World War II (O’Donnell and Kearsley, 2012). However, large-scale xylitol production was ignored with the end of World War II (Ur Rehman et al., 2013).
Xylitol has a growing global market (Gupta, 2018). Xylitol production started in Fin¬land in the 1970s after the development of mass-scale production of D-xylose by chro¬matographic separation of several woody hemicelluloses. After several studies evaluating the effectiveness of xylitol in reducing dental plaque in 1970, xylitol was widely researched and accepted globally as a natural sweetener approved by the U.S. Food and Drug Administration (FDA) (FDA-CFR-Code of Federal Regulations Title 21, 2019). More than 35 countries have approved the use of xylitol in food, pharmaceuticals, and health products, mainly in chewing gums, toothpastes, syrups, and confectionery (da Silva and Chandel, 2012).
... In addition to specific metabolites discussed in various parts of this article, diverse other food and feed ingredients are produced by microbial (Gupta and Prakash, 2018;Gupta et al., 2018;Holban and Grumezescu, 2017;McNeil et al., 2013) and enzymatic processes. Microbially produced ingredients include the many vitamins (Fang et al., 2017;Vandamme, 1992;Wang et al., 2021a), biopreservatives such as bacteriocins (Chen and Hoover, 2003;Gautam and Sharma, 2009;Perez et al., 2014;Silva et al., 2018;Yang et al., 2014), food acids (e.g., acetic acid, citric acid, other organic acids) (Sauer et al., 2008(Sauer et al., , 2013, amino acids (D'Este et al., 2018;Ikeda, 2003), biopolymers (Freitas et al., 2013;Gutiérrez, 2018) for food thickening, food colorants (Nigam and Luke, 2016;Sen et al., 2019;Zha et al., 2020) and antioxidants (Chandra et al., 2020;Lin et al., 2014), food and feed enzymes (Choct, 2006;Fernandes, 2010;Kermasha and Eskin, 2021;McNeil et al., 2013;Nunes and Kumar, 2018;Raveendran et al., 2018;Whitehurst and van Oort, 2010), fatty acids (Chi et al., 2022;Ghazani and Marangoni, 2022;Thevenieau and Nicaud, 2013), certain sweeteners (Rafiqul and Mimi Sakinah, 2013), flavoring agents (Krings and Berger, 1998;Lee and Trinh, 2020;Vandamme and Soetaert, 2002;Zha et al., 2020), and fragrances (Korn et al., 2020;Vilela et al., 2019). Compared to the more conventional production processes, many environmental and sustainability benefits are associated with enzymatic processes (Nedwin and Oxenbøll, 2005). ...
