Search Results (89)

This study aimed to evaluate the production of xylose reductase (XR), an enzyme responsible for converting xylose into xylitol, by Candida tropicalis ATCC 750 using hemicellulosic hydrolysate from cashew apple bagasse (CABHM) as a low-cost carbon source. The effects of temperature, aeration, and fluid dynamics on XR biosynthesis were also investigated. The highest XR production (1.53 U mL⁻¹) was achieved at 30 °C, with 8.3 g·L⁻¹ of xylitol produced by the yeast under microaerobic conditions, demonstrating that aeration and fluid dynamics are important factors in this process. Cellular metabolism and enzyme production decreased at temperatures above 35 °C. The maximum enzymatic activity was observed at pH 7.0 and 50 °C. XR is a heterodimeric protein with a molecular mass of approximately 30 kDa. These results indicate that CABHM is a promising substrate for XR production by C. tropicalis, contributing to the development of enzymatic bioprocesses for xylitol production from lignocellulosic biomass. This study also demonstrates the potential of agro-industrial residues as sustainable feedstocks in biorefineries, aligning with the principles of a circular bioeconomy. Full article

This study evaluates the feasibility of using banana peels as a substrate for cultivating fodder yeast biomass. Banana peels (BPs), representing approximately 38% of the total fruit weight, are rich in cellulose and hemicellulose, thus presenting a significant opportunity for valorisation. The study investigates the effects of microwave and ultrasound treatments on the hydrolysis efficiency of banana peels and the subsequent cultivation of yeast. Two yeast strains, Scheffersomyces stipitis and Meyerozyma guilliermondii, were cultivated in hydrolysates prepared using various methods, including acid–thermal, enzymatic, microwave, and ultrasound treatments. The results demonstrate that enzymatic hydrolysis following microwave or ultrasound pretreatment significantly enhances sugar release, supporting higher biomass yields. The maximum biomass concentration achieved was 7.68 g DM/L, with crude protein content reaching up to 45.46% DM. These results indicate that banana peels can be effectively utilised for single-cell protein production, providing a sustainable alternative for animal feed. The study underscores the potential of integrating microwave and ultrasound technologies in bioprocessing to enhance the efficiency and environmental sustainability of yeast cultivation. Full article

The worldwide demand for sustainable bioprocesses is undeniable, as well as for research aimed at the biotechnological exploitation of lignocellulosic materials, especially their hemicellulosic fractions rich in xylose. Various bioproducts can be obtained from these fractions, although some bottlenecks still exist, such as the presence in hemicellulosic hydrolysates of compounds that are toxic for microorganisms, which requires a previous step of detoxification to reduce them to non-inhibitory levels. The present investigation proposes the use of hydrotalcites as a new detoxifying agent for the hemicellulosic hydrolysate of sugarcane straw to produce xylitol by Candida tropicalis, aiming at a greater removal of phenolics and less loss of sugars. The design of these experiments was used for factorial effect analysis in a simultaneous way; the influences of pH and temperature were evaluated, considering the detoxification process at different times for both uncalcined and calcined hydrotalcite adsorbents. While for the calcined hydrotalcite, the temperature was the significant factor, for the uncalcined, there was also an influence of pH and little effect on the factors of yield and productivity. The effectiveness of hydrotalcites as demonstrated in this research, mainly regarding the ability to reduce the content of phenolic compounds in hydrolysates with a low loss of sugar content, followed by fermentability to produce xylitol, is a strong requirement for the proposition of these new adsorbents in investigations of the development of sustainable technologies for obtaining bioproducts in a biorefinery context. Full article

The valorization of agri-food wastes can provide value-added products, enzymes and biofuels. For the second-generation ethanol (2G) production, pulps rich in cellulose are desirable in order to release fermentable sugars. This study investigated the homemade biosynthesis of cellulases and hemicellulases via solid-state fermentation (SSF) using sugarcane bagasse (SB) and wheat bran (WB) for the growth of endophytic fungi (Beauveria bassiana, Trichoderma asperellum, Metarhizium anisopliae and Pochonia chlamydosporia). Cocktails with high enzymatic levels were obtained, with an emphasis for M. anisopliae in the production of β-glucosidase (83.61 U/g after 288 h) and T. asperellum for xylanase (785.50 U/g after 144 h). This novel M. anisopliae β-glucosidase demonstrated acidophile and thermotolerant properties (optimum activity at pH 5.5 and 60 °C and stability in a wide pH range and up to 60 °C), which are suitable for lignocellulose saccharifications. Hence, the M. anisopliae multi-enzyme blend was selected for the hydrolysis of raw and organosolv-pretreated corn straw (CS) and corncob (CC) using 100 CBU/g cellulose. After the ethanol/water (1:1) pretreatment, solid fractions rich in cellulose (55.27 in CC and 50.70% in CS) and with low concentrations of hemicellulose and lignin were found. Pretreated CC and CS hydrolysates reached a maximum TRS release of 12.48 and 13.68 g/L, with increments of 100.80 and 73.82% in comparison to untreated biomass, respectively, emphasizing the fundamental role of a pretreatment in bioconversions. This is the first report on β-glucosidase biosynthesis using M. anisopliae and its use in biomass hydrolysis. These findings demonstrated a closed-loop strategy for internal enzyme biosynthesis integrated to reducing sugar release which would be applied for further usage in biorefineries. Full article

This work addresses the technical–economic–environmental analysis of a 1G2G ethanol integrated process using immobilized recombinant Saccharomyces cerevisiae and crude sugarcane bagasse acid hydrolysate mixed with molasses. Three case studies were evaluated and compared with the traditional 1G plants. The minimal ethanol-selling price and the life cycle assessment using CML-IA midpoint indicators were chosen as the economic and environmental metrics, respectively. The values found for the ethanol-selling price ranged from 472.92 USD/m³ to 966.53 USD/m³ for the integrated case studies. Compared to the average sales value of 1G ethanol (673.48 USD/m³), the first and second case studies were interesting for their economic viability, while the third case study would require a 43.5% increase in the price of ethanol to achieve production profitability. In the environmental assessment, the integrated 2G ethanol processes of the first and third case studies allowed for the increase in ethanol production per ton of sugarcane processed without decreasing the environmental performance of the process. The third case study presented the lowest environmental impact indicators, except for global warming potential and photochemical oxidation categories, highlighting the importance of the development of biomass pretreatment strategies with lower carbon footprint. The strategy of integrating the 2G process into a 1G ethanol biorefinery offers interesting economic and environmental values, allows the use of hemicellulose, and contributes to the development of 2G processes in sugarcane biorefineries and to the sustainability of the processes. Full article

A hemicellulose-first approach can offer advantages for biorefineries utilizing wheat straw as it combines lignocellulose fractionation and potentially higher added value from pentose-based hemicellulose. Therefore, a tailored hydrothermal concept for the production of xylooligosaccharides and xylan was investigated. The focus was on assessing the energy requirements and potential improvements based on experimental results. The wheat straw pretreatment and the downstream processing of hemicellulose hydrolysate were modeled at a scale of 30,000 tons of wheat straw dry mass per year. The results confirmed that the hydrothermal concept can be implemented in an energy-efficient manner without the need for additional auxiliaries, due to targeted process design, heat integration and a high solids loading during hydrolysis. The resulting specific energy requirements for pretreatment and hydrolysate processing are 0.28 kWh/kg and 0.13 kWh/kg of wheat straw dry mass, respectively. Compared to thermal hydrolysate processing alone, the combination of a multi-effect evaporator and pressure-driven ultrafiltration can reduce the heating and cooling energy by 29% and 44%, respectively. However, the ultrafiltration requirements (e.g., electrical energy, membrane area and costs) depend heavily on the properties of the hydrolysate and its interactions with the membrane. This work can contribute to the commercially viable ramp-up of wheat straw multi-product biorefineries. Full article

A biocatalyst has been developed for application in the simultaneous isomerization and fermentation (SIF) of xylose, which could enable operation in repeated batches and the use of xylose from biomass hemicellulose for the production of second-generation (2G) ethanol. To this end, the enzyme xylose isomerase (XI) was immobilized on eleven different supports (based on chitosan, modified silica, agarose and magnetic supports) to obtain a derivative that is stable under process conditions and easy to recover from the fermented medium for future industrial application in biorefineries. Immobilization was performed with 5 mg/g_support, with a support-to-suspension ratio of 1:20. Phosphate (pH 7.0) and carbonate–bicarbonate (pH 10.05) buffer were used for uni-point and multi-point immobilization, respectively. Among the immobilized enzymes, the magnetic microparticle Captura N exhibited the best immobilization parameters (67% recovered activity and half-life of 10 h at 80 °C), in addition to its magnetic properties, which facilitates purification. The SIF of crude sugarcane straw acid hydrolysate was carried out in repeated batches using XI-chitosan and XI-Captura N. Although economically promising, chitosan-based supports did not enhance enzyme stability. Therefore, magnetic microparticles are a promising option as XI immobilization supports for biorefinery applications. Full article

A sequential valorization process of sunflower stalks was carried out using nitric acid (0.1–2 mol dm⁻³) as a hydrolytic agent and fermenting the hydrolysate of higher sugar concentration in the presence of the non-conventional yeast Hansenula polymorpha. Values reached for ethanol yield (0.25 g g⁻¹) and xylitol yield (0.14 g g⁻¹) were higher than those achieved after pretreatment with other acids in previous studies. The effect of acid treatment with nitric, phosphoric, and sulfuric acids on the separated solid fractions was evaluated to determine its potential use as solid biofuel by FTIR and SEM determinations. A significant loss of lignin and hemicellulose was found in the solid treated with nitric acid, while a higher HHV was obtained when pretreated with phosphoric acid (19.16 MJ kg⁻¹) and sulfuric acid (19.12 MJ kg⁻¹). A subsequent enzymatic hydrolysis of acid-pretreated solids showed that the nitric acid pretreatment increased the availability of glucose from the cellulose fraction to a greater extent than the other two acids, by reducing the hemicellulose fraction to 0.7% and the lignin fraction to 2.5%. This study shows that pretreatment of biomass with nitric acid leads to better fermentation results to obtain biofuels such as ethanol, which could be further increased by additional enzymatic hydrolysis, while pretreatment with the other two acids generates better solid fuels. Full article

Converting agricultural biomass wastes into bio-chemicals can significantly decrease greenhouse gas emissions and foster global initiatives towards mitigating climate change. This study examined the co-production of xylitol and ethanol from xylose and glucose-rich hydrolysates of corn cob (CC), sugarcane bagasse (SCB), and rice straw (RS) without prior detoxification, using C. magnoliae (C. mag), C. tropicalis (C. trop), and C. guilliermondii (C. guil). A score ranking system based on weighted yields and productivity assessed the best raw material and yeast strain combination. The study revealed that C. mag cultivated on RS hemicellulosic and CC cellulosic media exhibited statistically significant (p ≤ 0.05) superiority in xylitol (272 ± 5) and ethanol 273 ± 3, production. The single-phase emulsion system using frozen-thawed whole cells of CC—C. mag, CC—C. trop, and RS—C. guil was utilized for phenylacetylcarbinol (PAC) biotransformation. Although similar PAC concentration within 14.4–14.7 mM was obtained, the statistically significant higher (p ≤ 0.05) volumetric pyruvate decarboxylase (PDC) activity from C. mag at 360 min was observed by 28.3 ± 1.51%. Consequently, further utilization of CC—C. mag in a two-phase emulsion system (Pi buffer: vegetable oil (Vg. oil) and Pi buffer: deep eutectic solvents (DES)) revealed that Pi buffer: DES medium preserved volumetric PDC activity (54.0 ± 1.2%) statistically significant higher (p ≤ 0.05) than the Pi buffer: Vg. oil system (34.3 ± 1.3%), with no statistically significant difference (p > 0.05) in [PAC]. These findings outlined the sustainable pioneering approach for the co-production of chemicals and reusing the residual yeast cells for PAC biotransformation in the Pi buffer: DES system. Full article

Due to its unique physicochemical properties, Pullulan is an exopolysaccharide with many applications in the food, biomedical, and pharmaceutical industries. Aiming to reduce its production cost, an interesting alternative is to consider other possibilities of raw materials, including the production of this biopolymer in a lignocellulosic biorefinery concept. Xylose is the main sugar of hemicellulosic hydrolysates obtained from different biomasses, and it is a sugar still not extensively exploited regarding its potential for pullulan production. This study aimed to evaluate the production of pullulan from sugarcane bagasse hemicellulosic hydrolysate by cultivating Aureobasidium pullulans ATCC 42023 in a bubble column reactor. The hemicellulosic hydrolysate was obtained through dilute acid treatment carried out in a stirred tank reactor before being detoxified to remove microbial growth inhibitors. The maximum concentration of 28.62 ± 1.43 g/L of pullulan was obtained after 120 h of fermentation in a bubble column reactor in batch mode. Analysis of spectroscopic properties through FTIR of the obtained pullulan revealed α-(1→6)-linked maltosyl units, similar to those of commercial samples of the biopolymer. XRD analysis showed that the prepared pullulan is amorphous, and a homogeneous morphology with a smooth surface of the pullulan was observed in SEM analysis. This study showed the potential of the production of pullulan from sugarcane bagasse hemicellulosic hydrolysate in a bubble column bioreactor, an alternative strategy for the industrial production of this biopolymer. Full article

Sugarcane bagasse (SCB), an agro-industrial byproduct generated by a sugar mill, holds a substantial carbohydrate content of around 70 wt.%, comprising cellulose and hemicellulose. Saccharification plays a pivotal role in the conversion of SCB into second-generation (2G)-ethanol and valuable compounds, which is significantly aided by thermochemical pretreatments. In this study, SCB underwent diluted sulfuric acid pretreatment (2% H₂SO₄, 80 rpm, 200 °C, 20 min), resulting in the removal of 77.3% of the xylan. The hemicellulosic hydrolysate was analyzed to identify the sugars and degraded products acting as microbial inhibitors. The acid hydrolysate showed a xylose yield of 68.0% (16.4 g/L) and a yield of 3.8 g/L of acetic acid. Afterward, the hemicellulosic hydrolysate was concentrated 2.37 times to obtain a xylose-rich stream (39.87 g/L). The sequential detoxification, employing calcium oxide and activated carbon, removed the inhibitory compounds, including acetic acid, while preserving the xylose at 38.10 g/L. The enzymatic saccharification of cellulignin at 5% and 10% of the total solids (TSs) yielded comparable reducing sugar (RS) yields of 47.3% (15.2 g/L) and 47.4% (30.4 g/L), respectively, after 96 h, employing a 10 FPU/g enzyme loading of Cellic^® CTec3 (Novozymes Inc. Parana, Brazil). In summary, these findings outline an integrated green chemistry approach aimed at addressing the key challenges associated with pretreatment, concentration, detoxification, and enzymatic hydrolysis to produce fermentable sugars. Full article

In this work, hydrogen production from the co-digestion of sugarcane straw and sugarcane vinasse in the dark fermentation (DF) process was monitored using a cost-effective hydrogen detection system. This system included a sensor of the MQ-8 series, an Arduino Leonardo board, and a computer. For the DF, different concentrations of sugarcane vinasse and volumetric ratios of vinasse/hemicellulose hydrolysate were used together with a thermally pretreated inoculum, while the hydrogen detection system stored the hydrogen concentration data during the fermentation time. The results showed that a higher concentration of vinasse led to higher inhibitors for the DF, resulting in a longer lag phase. Additionally, the hydrogen detection system proved to be a useful tool in monitoring the DF, showcasing a rapid response time, and providing reliable information about the period of adaptation of the inoculum to the substrate. The measurement system was assessed using the error metrics SE, RMSE, and MBE, whose values ranged 0.6 and 5.0% as minimum and maximum values. The CV (1.0–8.0%) and SD (0.79–5.62 ppm) confirmed the sensor’s robustness, while the ANOVA at the 5% significance level affirmed the repeatability of measurements with this instrument. The RMSE values supported the accuracy of the sensor for online measurements (6.08–14.78 ppm). The adoption of this straightforward and affordable method sped up the analysis of hydrogen in secluded regions without incurring the expenses associated with traditional measuring instruments while offering a promising solution for biomass valorization, contributing to the advancement of rural green energy initiatives in remote areas. Full article

Sugarcane bagasse (SCB) is an abundant agricultural waste, rich in cellulose and hemicellulose, that could be used as an ideal raw material for succinic acid (SA) production. A two-step chemical pretreatment, involving alkali extraction and alkaline hydrogen peroxide treatment, was utilized to treat SCB, followed by multi-enzyme hydrolysis to obtain a reducing sugar hydrolysate mainly composed of glucose and xylose. Optimization of the multi-enzyme hydrolysis of pretreated SCB resulted in a final reducing sugar concentration of 78.34 g/L. In order to enhance the bioconversion of SCB to SA and to reduce the production costs, the initial reducing sugar concentration, nitrogen source, and MgCO₃ content were further optimized. The results demonstrated that the inexpensive corn steep liquor powder (CSLP) could be utilized as an alternative nitrogen source to yeast extract for the production of SA; and the optimal concentrations of initial reducing sugar, CSLP, and MgCO₃ were 70 g/L, 18 g/L, and 60 g/L, respectively. When fed-batch fermentation was conducted in a 2 L stirred bioreactor, approximately 72.9 g/L of SA was produced, with a yield of 83.2% and a productivity of 1.40 g/L/h. The high SA concentration, yield, and productivity achieved in this study demonstrate the potential of SCB, an agricultural waste, as a viable alternative substrate for Actinobacillus succinogenes GXAS137 to produce SA. This lays a solid foundation for the resource utilization of agricultural waste and cost-effective industrial-scale production of SA in the future. Full article

The extracted olive pomace (EOP) is an industrial lignocellulosic by-product of olive pomace oil extraction, currently mainly used for energy production through combustion. In this work, the hemicellulosic fraction of EOP was selectively hydrolyzed by diluted acid hydrolysis to obtain pentose-rich hydrolysates that can potentially be upgraded by Debaryomyces hansenii, targeting xylitol production. The monosaccharides and degradation by-products released along the pre-treatment were quantified and several detoxification methods for the removal of potentially toxic compounds were evaluated, including pH adjustment to 5.5, the use of anion-exchange resins, adsorption into activated charcoal, concentration by evaporation, and membrane techniques, i.e., nanofiltration. The latter approach was shown to be the best method allowing the full removal of furfural, 41% of 5-hydroxymethylfurfural, 54% of acetic acid, and 67% of the phenolic compounds present in the hydrolysate. The effects of the supplementation of both non-detoxified and detoxified hydrolysates were also assessed. The non-detoxified hydrolysate, under aerobic conditions, supported the yeast growth and xylitol production at low levels. Supplementation with the low-cost corn steep liquor of the nanofiltration detoxified hydrolysate showed a higher xylitol yield (0.57 g/g) compared to the non-detoxified hydrolysate. The highest xylitol productivity was found in hydrolysate detoxified with anionic resins (0.30 g/L·h), which was 80% higher than in the non-detoxified culture medium. Overall, the results showed that EOP dilute acid hydrolysates can efficiently be used for xylitol production by D. hansenii if detoxification, and supplementation, even with low-cost supplements, are performed. Full article

This study explores the mechanical properties, as well as the water-reducing and setting delay mechanism, of a novel xylonic acid-based water reducer applied to cementitious materials. Four xylonic acid water reducers were synthesized in this study: XACa (PX) from pure xylose, XACa (HS) from hemicellulose hydrolysate, XANa (PX) from pure xylose, and XANa (HS) from hemicellulose hydrolysate. These were generated through the whole-cell catalysis of Gluconobacter oxydans bacteria, using pure xylose and hemicellulose hydrolysate as substrates. The findings indicate that the xylonic acid-based water reducer can attain a water-reducing capability between 14% and 16% when the dosage (expressed as a mass fraction of cement) is roughly 0.2%. In initial and final setting tests, XACa (PX) demonstrated a pronounced retarding influence at admixture levels below 0.15%, reaching its apex at 0.10%. This delayed the initial setting time by 76% and the final setting time by 136% relative to the control group. However, a slight pro-setting effect was noted beyond a 0.2% dosage. In the compressive and flexural tests of concrete, under the same slump, the XA group improved its mechanical properties by 5% to 10% compared to the SodiuM lignosulfonate (SL) group. In the air content and chloride ion migration resistance tests, the XA group reduced the air content by 38% compared to the SL group, but also increased the data of rapid chloride migration (D_RCM) by 16%. Characterization studies revealed that the carboxyl and hydroxyl groups in xylonic acid undergo chemisorption with the Si-O bonds on the surface of cement particles. These groups interact with the Si-O bonds on cement particles, contributing to water-reducing effects and delaying the setting process by impeding Ca²⁺ ion aggregation in the calcium-silicate-hydrate gel. Its significant water-reducing effect, adjustable setting time, and excellent mechanical and durability properties suggest its viability as an alternative to lignosulfonate series water-reducing agents. Full article