Physico-chemical pretreatment and enzymatic hydrolysis of cotton stalk for ethanol production by Saccharomyces cerevisiae

Microbial β-glucosidases: Recent advances and applications

The global β-glucosidase market is currently estimated at ∼400 million USD, and it is expected to double in the next six years; a trend that is mainly ascribed to the demand for the enzyme for biofuel processing. Microbial β-glucosidase, particularly, has thus garnered significant attention due to its ease of production, catalytic efficiency, and versatility, which have all facilitated its biotechnological potential across different industries. Hence, there are continued efforts to screen, produce, purify, characterize and evaluate the industrial applicability of β-glucosidase from actinomycetes, bacteria, fungi, and yeasts. With this rising demand for β-glucosidase, various cost-effective and efficient approaches are being explored to discover, redesign, and enhance their production and functional properties. Thus, this present review provides an up-to-date overview of advancements in the utilization of microbial β-glucosidases as "Emerging Green Tools" in 21st-century industries. In this regard, focus was placed on the use of recombinant technology, protein engineering, and immobilization techniques targeted at improving the industrial applicability of the enzyme. Furthermore, insights were given into the recent progress made in conventional β-glucosidase production, their industrial applications, as well as the current commercial status-with a focus on the patents.

Delignification of the cotton stalk and ginning mill waste via EnZolv pretreatment and optimization of process parameters using response surface methodology (RSM)

The present study aimed to add value to cotton waste biomass using a more eco-friendly process, EnZolv which delignifies cotton stalk and cotton ginning mill waste. A maximum delignification of 68.68% and 65.51% was obtained using pre-optimized EnZolv parameters in cotton stalk (CS) and ginning mill waste (GMW), respectively. Optimized EnZolv process removed 78.68% of lignin in CS using Response Surface Methodology (RSM) in Box-Behnken design at 0% moisture content, 50 U laccase g-1 of biomass, 5 h incubation time, 50 ⁰C incubation temperature, and 150 rpm shaking speed. Similarly, RSM-based delignification of 70.53% in GMW was achieved under the optimized EnZolv conditions of 98.75 % moisture content, 41.59 U laccase g-1 of biomass, 9.3 h incubation time, 46.15 ⁰C incubation temperature, and 150 rpm shaking speed.

Bioethanol production from agricultural residues as lignocellulosic biomass feedstock's waste valorization approach: A comprehensive review

Bioenergy is becoming very popular, drawing attention as a renewable energy source that may assist in managing growing energy costs, besides possibly affording revenue to underprivileged farmers and rural populations worldwide. Bioethanol made from agricultural residual-biomass provides irreplaceable environmental, socioeconomic, and strategic benefits and can be considered as a safe and cleaner liquid fuel alternative to traditional fossil fuels. There is a significant advancement made at the bench scale towards fuel ethanol production from agricultural lignocellulosic materials (ALCM). These process technologies include pretreatment of ALCM biomass employment of cellulolytic enzymes for depolymerizing carbohydrate polymers into fermentable sugars to effectively achieve it by applying healthy fermentative microbes for bioethanol generation. Amongst all the available process methods, weak acid hydrolysis followed by enzymatic hydrolysis process technique. Recovering higher proficient celluloses is more attractive in terms of economic benefits and long-term environmental effects. Besides, the state of ALCM biomass based bioethanol production methods is discussed in detail, which could make it easier for the scientific and industrial communities to utilize agricultural leftovers properly.

High-pressure microwave-assisted pretreatment of softwood, hardwood and non-wood biomass using different solvents in the production of cellulosic ethanol

BACKGROUND

Pretreatment is an indispensable stage of the preparation of lignocellulosic biomass with key significance for the effectiveness of hydrolysis and the efficiency of the production of cellulosic ethanol. A significant increase in the susceptibility of the raw material to further degradation can be attained as a result of effective delignification in high-pressure conditions. With this in mind, a method of high-pressure pretreatment using microwave radiation and various solvents (water, 40% w/v NaCS, 1% v/v H₂SO₄, 1% w/v NaOH or 60% v/v EtOH with an addition of 1% v/v H₂SO₄) was developed, enabling the acquisition of biomass with an increased susceptibility to the process of enzymatic hydrolysis. The medium obtained in this way can be used for the production of cellulosic ethanol via high-gravity technology (lignocellulosic media containing from 15 to 20% dry weight of biomass). For every type of biomass (pine chips, beech chips and wheat straw), a solvent was selected to be used during the pretreatment, guaranteeing the acquisition of a medium highly susceptible to the process of enzymatic hydrolysis.

RESULTS

The highest efficiency of the hydrolysis of biomass, amounting to 71.14 ± 0.97% (glucose concentration 109.26 ± 3.49 g/L) was achieved for wheat straw subjected to microwave-assisted pretreatment using 40% w/v NaCS. Fermentation of this medium produced ethanol concentration at the level of 53.84 ± 1.25 g/L. A slightly lower effectiveness of enzymatic hydrolysis (62.21 ± 0.62%) was achieved after high-pressure microwave-assisted pretreatment of beech chips using 1% w/v NaOH. The hydrolysate contained glucose in the concentration of 91.78 ± 1.91 g/L, and the acquired concentration of ethanol after fermentation amounted to 49.07 ± 2.06 g/L. In the case of pine chips, the most effective delignification was achieved using 60% v/v EtOH with the addition of 1% v/v H₂SO₄, but after enzymatic hydrolysis, the concentration of glucose in hydrolysate was lower than in the other raw materials and amounted to 39.15 ± 1.62 g/L (the concentration of ethanol after fermentation was ca. 19.67 ± 0.98 g/L). The presence of xylose and galactose was also determined in the obtained fermentation media. The highest initial concentration of these carbohydrates (21.39 ± 1.44 g/L) was observed in beech chips media after microwave-assisted pretreatment using NaOH. The use of wheat straw after pretreatment using EtOH with an addition of 1% v/v H₂SO₄ for the preparation of fermentation medium, results in the generation of the initial concentration of galactose and xylose at the level of 19.03 ± 0.38 g/L.

CONCLUSION

The achieved results indicate a high effectiveness of the enzymatic hydrolysis of the biomass subjected to high-pressure microwave-assisted pretreatment. The final effect depends on the combined use of correctly selected solvents for the different sources of lignocellulosic biomass. On the basis of the achieved results, we can say that the presented method indicates a very high potential in the area of its use for the production of cellulosic ethanol involving high-gravity technology.

Optimization and characterization of rhamnolipid production by Pseudomonas aeruginosa NY3 using waste frying oil as the sole carbon

Yield and cost are two major factors limiting the widespread use of rhamnolipids (RLs). In the present study, waste frying oil (WFO) was used as the sole carbon source to produce environmentally friendly RLs by Pseudomonas aeruginosa NY3. The Plackett-Burman design (PBD) and Box-Behnken design (BBD) methods were used to maximize the production yield of RL. The PBD results showed that the concentrations of NaNO₃ , Na₂ HPO₄ , and trace elements were the key factors affecting the yield of RL. Furthermore, the BBD results showed that at NaNO₃ , Na₂ HPO₄ , and trace elements concentrations were 4.95, 0.66, and 0.64 mL/L, respectively, the average RL yield reached 9.15 ± 0.52 g/L, 1.58-fold higher than that observed before optimization. Fourier transform infrared spectroscopy (FTIR) and liquid chromatography-ion trap-time of flight mass spectrometry (LCMS-IT-TOF) were used to elucidate the diversity of RL congeners. The results showed that, after optimization, the RL congener diversity increased, and the major RL constituent was converted from di-RLs (64.04%) to mono-RLs (60.44%). These results suggested that the concentrations of the components contained in the culture medium of P. aeruginosa NY3 influenced not only the yield of RL, but also its congener distribution.

Organic waste streams as feedstock for the production of high volume-low value products

Valorisation of organic wastes to produce industrially relevant commodity products is a sustainable, cost-effective and viable alternative providing a green platform for chemical production while simultaneously leading to waste disposal management. In the present study, organic wastes such as agricultural residue-derived sugars, oilseed meals, poultry waste and molasses were used for substituting expensive organic fermentation medium components. Moorella thermoacetica and Aurantiochytrium limacinum were adapted on these waste-derived hydrolysates to produce high volume-low value products such as bio-acetic acid (80% theoretical yields) and oil-rich fish/animal feed (more than 85% dry cell weight as compared with conventional nutrient sources) respectively. Use of these waste-derived nutrients led to ~ 75% and ~ 90% reduction in media cost for acetic acid and oil-rich biomass production respectively as compared with that of traditionally used high-priced medium components. The strategy will assist in the cost reduction for high volume-low value products while also ensuring waste recovery.

Suitability assessment of dumpsite soil biocover to reduce methane emission from landfills under interactive influence of nutrients

Biocovers are known for their role as key facilitator to reduce landfill methane (CH₄) emission on improving microbial methane bio-oxidation. Methanotrophs existing in the aerobic zone of dumped wastes are the only known biological sinks for CH₄ being emitted from the lower anaerobic section of landfill sites and even from the atmosphere. However, their efficacy remains under the influence of landfill environment and biocover characteristics. Therefore, the present study was executed to explore the suitability and efficacy of dumpsite soil as biocover to achieve enhanced methane bio-oxidation under the interactive influence of nutrients, carbon source, and environmental factors using statistical-mathematical models. The Placket-Burman design (PBD) was employed to identify the significant factors out of 07 tested factors having considerable impact on CH₄ bio-oxidation. The normal plot and Student's t test of PBD indicated that ammonical nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N), methane (CH₄), and copper (Cu) concentration were found significant. A three-level Box-Behnken design (BBD) was further applied to optimize the significant factors identified from PBD. The BBD results revealed that interactive interaction of CH₄ with NH₄⁺-N and NO₃^--N affected the CH₄ bio-oxidation significantly. The sequential statistical approach predicted that maximum CH₄ bio-oxidation of 27.32 μg CH₄ h^-1 could be achieved with CH₄ (35%), NO₃^--N (250 μg g^-1), NH₄+-N (25 μg g^-1), and Cu (50 mg g^-1) concentration. Conclusively, waste dumpsite soil could be a good alternative over conventional soil cover to improve CH₄ bio-oxidation and lessen the emission of greenhouse gas from waste sector.

Anti-Streptococcus mutans and anti-biofilm activities of dextranase and its encapsulation in alginate beads for application in toothpaste

Background

The accumulation of plaque causes oral diseases. Dental plaque is formed on teeth surfaces by oral bacterial pathogens, particularly Streptococcus mutans, in the oral cavity. Dextranase is one of the enzymes involved in antiplaque accumulation as it can prevent dental caries by the degradation of dextran, which is a component of plaque biofilm. This led to the idea of creating toothpaste containing dextranase for preventing oral diseases. However, the dextranase enzyme must be stable in the product; therefore, encapsulation is an attractive way to increase the stability of this enzyme.

Methods

The activity of food-grade fungal dextranase was measured on the basis of increasing ratio of reducing sugar concentration, determined by the reaction with 3, 5-dinitrosalicylic acid reagent. The efficiency of the dextranase enzyme was investigated based on its minimal inhibitory concentration (MIC) against biofilm formation by S. mutans ATCC 25175. Box-Behnken design (BBD) was used to study the three factors affecting encapsulation: pH, calcium chloride concentration, and sodium alginate concentration. Encapsulation efficiency (% EE) and the activity of dextranase enzyme trapped in alginate beads were determined. Then, the encapsulated dextranase in alginate beads was added to toothpaste base, and the stability of the enzyme was examined. Finally, sensory test and safety evaluation of toothpaste containing encapsulated dextranase were done.

Results

The highest activity of the dextranase enzyme was 4401.71 unit/g at a pH of 6 and 37 °C. The dextranase at its MIC (4.5 unit/g) showed strong inhibition against the growth of S. mutans. This enzyme at 1/2 MIC also showed a remarkable decrease in biofilm formation by S. mutans. The most effective condition of dextranase encapsulation was at a pH of 7, 20% w/v calcium chloride and 0.85% w/v sodium alginate. Toothpaste containing encapsulated dextranase alginate beads produced under suitable condition was stable after 3 months of storage, while the sensory test of the product was accepted at level 3 (like slightly), and it was safe.

Conclusion

This research achieved an alternative health product for oral care by formulating toothpaste with dextranase encapsulated in effective alginate beads to act against cariogenic bacteria, like S. mutants, by preventing dental plaque.

Enhancing the Enzymatic Saccharification of Grain Stillage by Combining Microwave-Assisted Hydrothermal Irradiation and Fungal Pretreatment

Grain stillage from the liquor industry was pretreated by using microwave-assisted hydrothermal pretreatment, fungal pretreatments, and their combination to enable efficient enzymatic hydrolysis for sugar production. The microwave-assisted hydrothermal (MH) pretreatment was optimized by using a response surface methodology, and the respective maximum reducing sugar yield and saccharification efficiency of 17.59 g/100 g and 33.85%, respectively, were achieved under the pretreatment conditions of microwave power = 120 W, solid-to-liquid ratio = 1:15 (g·mL^-1), and time = 3.5 min. The fungal pretreatment with Phanerochaete chrysosporium digestion (PC) achieved the maximum ligninolytic enzyme activities in 6 days with 10% inoculum size at which the reducing sugar yield and saccharification efficiency reached 19.74 g/100 g and 36.29%, respectively. To further improve the pretreatment efficiency, MH and PC pretreatments were combined, but the sequence of MH and PC mattered on the saccharification efficiency. The MH + PC pretreatment (the MH prior to the PC) was better than PC + MH (the PC prior to the MH) in terms of saccharification efficiency. Overall, the MH + PC pretreatment achieved superior reducing sugar yield and saccharification efficiency (25.51 g/100 g and 66.28%, respectively) over all other studied pretreatment methods. The variations of chemical compositions and structure features of the raw and pretreated grain stillage were characterized by using scanning electron microscopy and Fourier transform infrared spectroscopy. The results reveal that both MH and PC pretreatments mainly functioned on delignification and decreasing cellulose crystallinity, thus enhancing the enzymatic saccharification of the pretreated grain stillage. The combined MH and PC pretreatment could be a promising method to enable cost-efficient grain stillage utilization for downstream applications such as biofuels.

Microbial Beta Glucosidase Enzymes: Recent Advances in Biomass Conversation for Biofuels Application

The biomass to biofuels production process is green, sustainable, and an advanced technique to resolve the current environmental issues generated from fossil fuels. The production of biofuels from biomass is an enzyme mediated process, wherein β-glucosidase (BGL) enzymes play a key role in biomass hydrolysis by producing monomeric sugars from cellulose-based oligosaccharides. However, the production and availability of these enzymes realize their major role to increase the overall production cost of biomass to biofuels production technology. Therefore, the present review is focused on evaluating the production and efficiency of β-glucosidase enzymes in the bioconversion of cellulosic biomass for biofuel production at an industrial scale, providing its mechanism and classification. The application of BGL enzymes in the biomass conversion process has been discussed along with the recent developments and existing issues. Moreover, the production and development of microbial BGL enzymes have been explained in detail, along with the recent advancements made in the field. Finally, current hurdles and future suggestions have been provided for the future developments. This review is likely to set a benchmark in the area of cost effective BGL enzyme production, specifically in the biorefinery area.

Optimization of extraction conditions and determination of purine content in marine fish during boiling

Background

Gout is the second most common metabolic disease affecting human health. The disease of gout is closely related to the level of uric acid, which is the end-product of human purine metabolism. Moreover, food is the main way of external ingestion of purine.

Method

A simple and time-saving method was developed to extract purines like adenine, hypoxanthine, guanine, and xanthine from marine fish by single factor design combined with Box-Behnken. The contents of these purines in the edible parts and internal organs of marine fish, as well as Scophthalmus maximus, were determined by high-performance liquid chromatography to investigate the relationship between the boiling process and purine content.

Result

The mixed-acid method was chosen for the extraction of purine bases and the extraction conditions were as follows: mixture acid 90.00% TFA/80.00% FA (v/v, 1:1); hydrolysis temperature 90.00 °C; time 10.00 min; liquid-to-solid ratio 30:1. The total purine content of the edible parts (eyes, dorsal muscles, abdominal muscles, and skin) was the highest in Scophthalmus maximus, followed by sphyraena, Sardinella, Trichiurus lepturus, Scomberomorus niphonius, Pleuronectiformes, Sea catfish, Anguillidae, and Rajiformes. Moreover, boiling significantly reduced the purine content in the marine fish because of the transfer of the purines to the cooking liquid during boiling. Scophthalmus maximus, Sphyraena, and Sardinella were regard as high-purine marine fish, which we should eat less. We also confirmed that boiling significantly transferred purine bases from fish to cooking liquid. Thus, boiling could reduce the purine content of fish, thereby reducing the risk of hyperuricemia and gout.

Lignin monomer in steam explosion assist chemical treated cotton stalk affects sugar release

In this study, the fermentable sugar released from cotton stalk (CS), which were pretreated by instant catapult steam explosion (SE) combined with different concentrations of strong monobasic acid (HCl), weak monobasic acid (CH₃COOH), strong monobasic alkali (NaOH) and weak monobasic alkali (NH₃·H₂O), followed by hydrolysis in cellulase/xylanase mixed enzyme solutions, were comparably investigated. The highest yield of 73.22% of fermentable sugar yield was obtained in SE-2.4 MPa-5%NH₃·H₂O treated CS substrates, which was 5.14 times higher than that from enzymatic hydrolysis (EH) of raw CS. Furthermore, evaluation of monolignins content (H, G, S) in different CS samples suggested that substrates rich in guaiacyl (G) and syringyl (S) would generate a higher efficiency of enzymatic saccharification. Therefore, the slight genetic modification of monolignins for cotton stalk might be a potential way to enhance biomass degradation and transformation.

Hydrogen Production from Energy Poplar Preceded by MEA Pre-Treatment and Enzymatic Hydrolysis

The need to pre-treat lignocellulosic biomass prior to dark fermentation results primarily from the composition of lignocellulose because lignin hinders the processing of hard wood towards useful products. Hence, in this work a two-step approach for the pre-treatment of energy poplar, including alkaline pre-treatment and enzymatic saccharification followed by fermentation has been studied. Monoethanolamine (MEA) was used as the alkaline catalyst and diatomite immobilized bed enzymes were used during saccharification. The response surface methodology (RSM) method was used to determine the optimal alkaline pre-treatment conditions resulting in the highest values of both total released sugars (TRS) yield and degree of lignin removal. Three variable parameters (temperature, MEA concentration, time) were selected to optimize the alkaline pre-treatment conditions. The research was carried out using the Box-Behnken design. Additionally, the possibility of the re-use of both alkaline as well as enzymatic reagents was investigated. Obtained hydrolysates were subjected to dark fermentation in batch reactors performed by Enterobacter aerogenes ATCC 13048 with a final result of 22.99 mL H₂/g energy poplar (0.6 mol H₂/mol TRS).

Environmental performances of coproducts. Application of Claiming-Based Allocation models to straw and vetiver biorefineries in an Indian context

Among the renewables, non-food and wastelands based biofuels are essential for the transport sector to achieve country's climate mitigation targets. With the growing interest in biorefineries, setting policy requirements for other coproducts along with biofuels is necessary to improve the products portfolio of biorefinery, increase the bioproducts perception by the consumers and push the technology forward. Towards this context, Claiming-Based allocation models were used in comparative life cycle assessment of multiple products from wheat straw biorefinery and vetiver biorefinery. Vetiver biorefinery shows promising Greenhouse gas emission savings (181-213%) compared to the common crop based lignocellulose (wheat straw) biorefinery. Assistance of Claiming-Based Allocation models favors to find out the affordable allocation limit (0-80%) among the coproducts in order to achieve the individual prospective policy targets. Such models show promising application in multiproduct life cycle assessment studies where appropriate allocation is challenging to achieve the individual products emission subject to policy targets.

Microwave-assisted ionic liquid-mediated rapid catalytic conversion of non-edible lignocellulosic Sunn hemp fibres to biofuels

Sunn hemp fibre - a cellulose-rich crystalline non-food energy crop, containing 75.6% cellulose, 10.05% hemicellulose, 10.32% lignin, with high crystallinity (80.17%) and degree of polymerization (650) - is identified as a new non-food substrate for lignocellulosic biofuel production. Microwave irradiation is employed to rapidly rupture the cellulose's glycosidic bonds and enhance glucose yield to 78.7% at 160 °C in only 46 min. The reactants - long-chain cellulose, ionic liquid, transition metal catalyst, and water - form a polar supramolecular complex that rotates under the microwave's alternating polarity and rapidly dissipates the electromagnetic energy through molecular collisions, thus accelerating glycosidic bond breakage. In 46 min, 1 kg of Sunn hemp fibres containing 756 g of cellulose produces 595 g of glucose at 160 °C, and 203 g of hydroxymethyl furfural (furanic biofuel precursor) at 180 °C. Yeast mediated glucose fermentation produces 75.6% bioethanol yield at 30 °C, and the ionic liquid is recycled for cost-effectiveness.