Improving β-glucosidase biocatalysis with deep eutectic solvents based on choline chloride

Biotransformation of ginsenoside compound K using β-glucosidase in deep eutectic solvents

Ginsenoside compound K (CK) holds significant potential for application in the pharmaceutical industry, which exhibits numerous pharmacological activity such as cardioprotective and antidiabetic. However, the difficult separation technique and limited yield of CK hinder its widespread use. The study investigated the process of converting ginsenoside CK using β-glucosidase. It aimed to determine the specific site where the enzyme binds and the most favorable arrangement of the enzyme. Molecular docking was also employed to determine the interaction between β-glucosidase and ginsenosides, indicating a strong and spontaneous contact force between them. The effectiveness of the conversion process was further improved using a "green" deep eutectic solvent (DES). A univariate experimental design was used to determine the composition of DES and the optimal hydrolysis conditions for β-glucosidase to convert ginsenoside Rb1 into ginsenoside CK. The employment of β-glucosidase enzymatic hydrolysis in the synthesis of rare ginsenoside CK applying the environmentally friendly solvent DES is not only viable and effective but also appropriate for industrial use. The characterization methods confirmed that DES did not disrupt the structure and conformation of β-glucosidase. In ChCl:EG = 2:1 (30%, v/v), pH 5.0 of DES buffer, reaction temperature 50 ℃, enzyme substrate mass ratio 1:1, after 36 h of reaction, the CK yield was 1.24 times that in acetate buffer, which can reach 86.2%. In this study, the process of using β-glucosidase enzymatic hydrolysis and producing rare ginsenoside CK in green solvent DES is feasible, efficient and suitable for industrial production and application.

Isolation and quantification of alginate in choline chloride-based deep eutectic solvents

Extraction of seaweed compounds using Deep Eutectic Solvents (DES) has shown high interest. Quantification, however, is challenging due to interactions with DES components. In this research work, three chemical separation techniques were investigated to isolate and quantify alginate from a set of choline chloride-based DES. While choline chloride served as the hydrogen bond acceptor (HBA); Urea, Ethylene Glycol, Propylene Glycol, Glycerol, Sorbitol, Xylitol and Glucose were used as hydrogen bond donors (HBD). DES containing sodium alginate were subjected to precipitation with sulfuric acid 0.2 M (pH 1.6), ethanol-water mixture (80 % v/v) and calcium chloride (1 % w/v CaCl2·2H2O). Alginate in precipitates was quantified and used to evaluate the performance of each separation technique. The highest recovery yields (51.2 ± 1.3 %) were obtained using the ethanol-water mixture followed by calcium chloride (45.7 ± 1.2 %), except for polyols (e.g. sorbitol). The lowest recovery yields were obtained with acid, with a particularly low recovery yield when urea was used as HBD (9.6 ± 1.3 %). Estimations of ManA/GulA ratios showed lower values for precipitates from DES compared to the ones obtained from water. This research shows ethanolic precipitation as a suitable method for alginate separation from the studied set of choline chloride-based DES.

Natural deep eutectic solvents-based green extraction of vanillin: optimization, purification, and bioactivity assessment

The sustainable extraction of natural compounds has recently attracted significant attention. The extraction of high-quality natural vanillin in active form is crucial for its efficient use in various industries, but conventional solvents are not suitable for this purpose. The flammability, volatility, and toxicity of organic solvents can harm extraction personnel, and their waste liquid can cause environmental pollution. Natural deep eutectic solvents (NADES) are cost-effective, environmentally friendly, biodegradable, and non-toxic organic alternative to conventional solvents. In this study, 20 different NADES were tested for the sustainable extraction of natural vanillin. Among these, a DES system composed of choline chloride: 1,4-butanediol: lactic acid exhibited the highest extraction rate (15.9 mg/g). Employing response surface methodology (RSM), optimal extraction conditions were determined, yielding a vanillin content 18.5 mg/g with water content of 33.9%, extraction temperature of 64.6°C, extraction time of 32.3 min, and a solid-liquid ratio of 44.9 mg/mL. Subsequently, the optimized NADES system was then assessed for reusability in extracting vanillin from vanilla pods and kraft lignin over three cycles, retaining 43% of its extraction efficiency and demonstrating potential for waste reduction. Purification of vanillin was achieved through chromatography using a non-polar resin SP700, with ethanol as a desorption eluent and a feed solution pH of 4.0, resulting in the highest vanillin purity. HPLC and GC-MS analyses confirmed purity, while antioxidant activity assays (DPPH and ABTS) showcased significant antioxidant activity of the purified vanillin. Moreover, vanillin exhibited notable antimicrobial activity against a panel of food-borne bacteria. This study introduces an environmentally friendly approach to vanillin extraction highlights using NADES, emphasizing the potential for producing high-quality bioactive vanillin with reduced environmental impact. The applicability of NADES systems extends beyond vanillin, offering a versatile method for extracting diverse natural compounds.

Microbial production and applications of β-glucosidase-A review

β-Glucosidase exists in all areas of living organisms, and microbial β-glucosidase has become the main source of its production because of its unique physicochemical properties and the advantages of high-yield production by fermentation. With the rise of the green circular economy, the production of enzymes through the fermentation of waste as the substrate has become a popular trend. Lignocellulosic biomass is an easily accessible and sustainable feedstock that exists in nature, and the production of biofuels from lignocellulosic biomass requires the involvement of β-glucosidase. This review proposes ways to improve β-glucosidase yield and catalytic efficiency. Optimization of growth conditions and purification strategies of enzymes can increase enzyme yield, and enzyme immobilization, genetic engineering, protein engineering, and whole-cell catalysis provide solutions to enhance the catalytic efficiency and activity of β-glucosidase. Besides, the diversified industrial applications, challenges and prospects of β-glucosidase are also described.

Natural deep eutectic solvent-A novel green solvent for protein stabilization

Natural deep eutectic solvents (NADESs) have been explored to provide a favorable environment for protein stabilization. In this context, NADESs were prepared with the molar ratio of trehalose to betaine ranging from 1:3 to 1:9 (NADES 1-3 to NADES 1-9). There was a strong hydrogen bond interaction between trehalose and betaine, and the interaction weakened with the reduction of trehalose. The NADES 1-7 had good thermal stability (-60-100 °C), low viscosity, and suitable pH (around 7). Trypsin had the highest relative enzyme activity in 50 % (v/v) NADES 1-7 under different temperatures, pH, and storage time. Furthermore, the changes in kinetic parameters indicated that the hydrogen bond environment of 50 % NADES 1-7 increased the contact between the substrate and the trypsin, speeding up the enzymatic reaction rate. This stabilizing effect mainly derived from the virtue of NADES 1-7 itself rather than the superposition of individual components. Additionally, spectral analysis revealed that the NADES 1-7 promoted trypsin conformational folding, effectively protecting the natural structure of trypsin. Importantly, the NADES 1-7 had good biocompatibility, further expanding its application.

Ambient 1,2-propanediol exposure accelerates the degradation of lipids and amino acids in milk via allosteric effects and affects the utilization of nutrients containing amide bond

The scandal of detecting 1, 2-propanediol (PL) in milk brought a crisis to the trust of consumers in the dairy industry, and the potential toxicity of PL has aroused the public concern about dietary exposure. A total of 200 pasteurized milk samples were collected from 15 regions, and the quantity of PL ranged between 0 and 0.31 g kg^-1. Pseudo-targeted quantitative metabolomics integrated with proteomics demonstrated that PL enhanced the reduction of κ-casein, β-casein, and 107 substances (41 amines and 66 amides) containing amide bonds. Pathway enrichment and topological analysis indicated that PL induced the metabolism of lipids, amino acids, oligosaccharide nucleotides, and alkaloids by accelerating the rate of nucleophilic reaction, and acetylcholinesterase, sarcosine oxidase, and prolyl 4-hydroxylase were determined as the vital enzymes related to the degradation of above nutrients. The results of molecular simulation calculation illustrated that the number of hydrogen bonds between acetylcholinesterase, sarcosine oxidase, and substrate increased to 2 and 3, respectively, while the position of hydrogen bonds between prolyl 4-hydroxylase and proline was shifted, indicating the change of conformation and the enhancement of hydrogen bond force were essential factors for the up-regulation of enzyme activity. This study first revealed the mechanism of deposition and transformation of PL in milk, which contributed to the knowledge of the quality control of milk and provided vital indicators to evaluate the adverse risks of PL in dairy products.

The attenuating ability of deep eutectic solvents towards the carboxylated multiwalled carbon nanotubes induced denatured β-lactoglobulin structure

The stabilization of proteins has been a major challenge for their practical utilization in industrial applications. Proteins can easily lose their native conformation in the presence of denaturants, which unfolds the protein structure. Since the introduction of deep eutectic solvents (DESs), there are numerous studies in which DESs act as promising co-solvents that are biocompatible with biomolecules. DESs have emerged as sustainable biocatalytic media and an alternative to conventional organic solvents and ionic liquids (ILs). However, the superiority of DESs over the deleterious influence of denaturants on proteins is often neglected. To address this, we present the counteracting ability of biocompatible DESs, namely, choline chloride-glycerol (DES-1) and choline chloride-urea (DES-2), against the structural changes induced in β-lactoglobulin (Blg) by carboxylated multiwalled carbon nanotubes (CA-MWCNTs). The work is substantiated with various spectroscopic and thermal studies. The spectroscopic results revealed that the fluorescence emission intensity enhances for the protein in DESs. Contrary to this, the emission intensity extremely quenches in the presence of CA-MWCNTs. However, in the mixture of DESs and CA-MWCNTs, there was a slight increase in the fluorescence intensity. Circular dichroism spectral studies reflect the reappearance of the native band that was lost in the presence of CA-MWCNTs, which is a good indicator of the counteraction ability of DESs. Further, thermal fluorescence studies showed that the protein exhibited extremely great thermal stability in both DESs as well as in the mixture of DES-CA-MWCNTs compared to the protein in buffer. This study is also supported by dynamic light scattering and zeta potential measurements; the results reveal that DESs were successfully able to maintain the protein structure. The addition of CA-MWCNTs results in complex formation with the protein, which is indicated by the increased hydrodynamic size of the protein. The presence of DESs in the mixture of CA-MWCNTs and DESs was quite successful in eliminating the negative impact of CA-MWCNTs on protein structural alteration. DES-1 proved to be superior to DES-2 over counteraction against CA-MWCNTs and maintained the native conformation of the protein. Overall, both DESs act as recoiling media for both native and unfolded (denatured by CA-MWCNTs) Blg structures. Both the DESs can be described as potential co-solvents for Blg with increased structural and thermal stability of the protein. To the best of our knowledge, this study for the first time has demonstrated the role of choline-based DESs in the mixture with CA-MWCNTs in the structural transition of Blg. The DESs in the mixture successfully enhance the stability of the protein by reducing the perturbation caused by CA-MWCNTs and then amplifying the advantages of the DESs present in the mixture. Overall, these results might find implications for understanding the role of DES-CA-MWCNT mixtures in protein folding/unfolding and pave a new direction for the development of eco-friendly protein-protective solvents.

Tyrosinase Magnetic Cross-Linked Enzyme Aggregates: Biocatalytic Study in Deep Eutectic Solvent Aqueous Solutions

In the field of biocatalysis, the implementation of sustainable processes such as enzyme immobilization or employment of environmentally friendly solvents, like Deep Eutectic Solvents (DESs) are of paramount importance. In this work, tyrosinase was extracted from fresh mushrooms and used in a carrier-free immobilization towards the preparation of both non-magnetic and magnetic cross-linked enzyme aggregates (CLEAs). The prepared biocatalyst was characterized and the biocatalytic and structural traits of free tyrosinase and tyrosinase magnetic CLEAs (mCLEAs) were evaluated in numerous DES aqueous solutions. The results showed that the nature and the concentration of the DESs used as co-solvents significantly affected the catalytic activity and stability of tyrosinase, while the immobilization enhanced the activity of the enzyme in comparison with the non-immobilized enzyme up to 3.6-fold. The biocatalyst retained the 100% of its initial activity after storage at -20 °C for 1 year and the 90% of its activity after 5 repeated cycles. Tyrosinase mCLEAs were further applied in the homogeneous modification of chitosan with caffeic acid in the presence of DES. The biocatalyst demonstrated great ability in the functionalization of chitosan with caffeic acid in the presence of 10% v/v DES [Bet:Gly (1:3)], enhancing the antioxidant activity of the films.

High-Value Bioconversion of Ginseng Extracts in Betaine-Based Deep Eutectic Solvents for the Preparation of Deglycosylated Ginsenosides

Deep eutectic solvents (DES), as a green alternative to traditional organic solvents in biocatalysis, not only activate proteins but even increase the efficiency of enzymatic reactions. Here, DES were used in a combinatorial enzyme-catalyzed system containing β-glucosidase BGLAt and β-galactosidase BGALAo to produce deglycosylated ginsenosides (De-g) from ginseng extracts (GE). The results showed that DES prepared with betaine and ethylene glycol (molar ratio, 1:2) could significantly stimulate the activity of the combinatorial enzymes as well as improve the acid resistance and temperature stability. The DES-based combinatorial enzyme-catalyzed system could convert 5 g of GE into 1.24 g of De-g (F1, F2, 20 (S)-PPT, and CK) at 24 h, which was 1.1 times that of the buffer sample. As confirmed by the spectral data, the changes in the conformations of the combinatorial enzymes were more favorable for the binding reaction with the substrates. Moreover, the constructed DES-based aqueous two-phase system enabled the recovery of substantial amounts of DES and De-g from the top phase. These results demonstrated that DES shows great application as a reaction solvent for the scale-up production of De-g and provide insights for the green extraction of natural products.

Combination of Enzymes and Deep Eutectic Solvents as Powerful Toolbox for Organic Synthesis

During the last decade, a wide spectrum of applications and advantages in the use of deep eutectic solvents for promoting organic reactions has been well established among the scientific community. Among these synthetic methodologies, in recent years, various examples of biocatalyzed processes have been reported, making use of eutectic mixtures as reaction media, as an improvement in terms of selectivity and sustainability. This review aims to show the newly reported protocols in the field, subdivided by reaction class as a 'toolbox' guide for organic synthesis.

An effect of choline lactate based low transition temperature mixtures on the lipase catalytic properties

A new series of low transition temperature mixures (LTTM) based on choline lactate quaternary ammonium salt and various hydrogen bond donors was prepared and characterized towards their physicochemical properties and usability as an enzymatic reaction mixture for lipase-catalyzed transesterification reactions. Studies of low transition temperature mixtures have shown a long-term stabilizing effect for lipase as well as a positive influence on lipase thermal stability. In the case of Ch[Lac]:Gly: EthGly increasing the stability of lipase by 8 °C (up to 55.2 °C) compared to the control sample. Conducted transesterification reactions were characterized by high yields - up to 98% - and high purity of the obtained products.

Current understanding and insights towards protein stabilization and activation in deep eutectic solvents as sustainable solvent media

Deep eutectic solvents (DESs) have emerged as a new class of green, designer and biocompatible solvents, an alternative to conventional organic solvents and ionic liquids (ILs) which are comparatively toxic and non-biodegradable. DESs are eutectic mixtures that are formed when a hydrogen bond acceptor (HBA) is mixed with a hydrogen bond donor (HBD) at particular molar ratios by mechanical grinding or under mild heating conditions. Very recently, these solvents have been the center of attention for researchers in biotechnology, biomedicine and various scientific applications. These environmentally benign solvents have a close analogy with ILs; however, they offer certain unique merits over traditional ILs. DESs display remarkable properties such as easy preparation, tunable composition, biodegradability, recyclability, inherently low toxicity, sustainability and biocompatibility; these special features validate DESs as new potential solvents/co-solvents for biomolecules. Mechanistically, the biocompatibility and protein friendly nature of DESs depend on various factors, which include the composition of the DES, viscosity and hydration level. Therefore, it becomes an essential task to bring together all the studies related to protein behaviour in DESs to unlock their biomolecular proficiency. This review specifically highlights recent insights into the biomacromolecular functionality in DESs, including outlines of the solubilization and stabilization of proteins, long term protein packaging, different extraction methods and enzyme activation in the presence of DESs. A literature survey reveals that DESs act as green media in which the protein structure and activity are retained. In some cases, proteins refolded and enzymatic activity was enhanced several fold in the presence of DESs. Furthermore, we have reviewed the possible mechanistic behaviour behind protein stabilization, refolding and activation in DESs. Overall, the main objective of this review is to explicate the advantages of the introduction of DESs for biomolecules and to demonstrate the versatility of these eco-friendly solvents for future bio-based applications.

Enhancing the Thermostability of Engineered Laccases in Aqueous Betaine-Based Natural Deep Eutectic Solvents

In recent years, natural deep eutectic solvents (NADESs) have gained increasing attention as promising nontoxic solvents for biotechnological applications, due to their compatibility with enzymes and ability to enhance their activity. Betaine-based NADESs at a concentration of 25 wt % in a buffered aqueous solution were used as media to inhibit thermal inactivation of POXA1b laccase and its five variants when incubated at 70 and 90 °C. All the tested laccases showed higher residual activity when incubated in NADES solutions, with a further enhancement achieved also for the most thermostable variant. Furthermore, the residual activity of laccases in the presence of NADESs showed a clear advantage over the use of NADESs' individual components. Molecular docking simulations were performed to understand the role of NADESs in the stabilization of laccases toward thermal inactivation, evaluating the interaction between each enzyme and NADESs' individual components. A correlation within the binding energies between laccases and NADES components and the stabilization of the enzymes was demonstrated. These findings establish the possibility of preincubating enzymes in NADESs as a facile and cost-effective solution to inhibit thermal inactivation of enzymes when exposed to high temperatures. This computer-aided approach can assist the tailoring of NADES composition for every enzyme of interest.

Biocompatible natural deep eutectic solvent-based extraction and cellulolytic enzyme-mediated transformation of Pueraria mirifica isoflavones: a sustainable approach for increasing health-bioactive constituents

The presence of specific gut microflora limits the biotransformation of Pueraria mirifica isoflavone (PMI) glycosides into absorbable aglycones, thus limiting their health benefits. Cellulolytic enzyme-assisted extraction (CAE) potentially solves this issue; however, solvent extraction requires recovery of the hydrophobic products. Here, we established the simultaneous transformation and extraction of PMIs using cellulolytic enzymes and natural deep eutectic solvents (NADESs). The NADES compositions were optimized to allow the use of NADESs as CAE media, and the extraction parameters were optimized using response surface methodology (RSM). The optimal conditions were 14.7% (v/v) choline chloride:propylene glycol (1:2 mol ratio, ChCl:PG) at 56.1 °C for the cellulolytic enzyme (262 mU/mL) reaction in which daidzin and genistin were extracted and wholly transformed to their aglycones daidzein and genistein. The extraction of PMIs using ChCl:PG is more efficient than that using conventional solvents; additionally, biocompatible ChCl:PG enhances cellulolytic enzyme activity, catalyzing the transformation of PMIs into compounds with higher estrogenicity and absorbability.

The study and application of biomolecules in deep eutectic solvents

Deep eutectic solvents offer stimulating possibilities for biomolecular stabilization and manipulation, biocatalysis, bioextraction, biomass processing, and drug delivery and therapy.

Enzymatic hydrolysis and extraction of ginsenoside recovered from deep eutectic solvent-salt aqueous two-phase system

Rare ginsenoside CK was recognized as a popular functional food because of superior pharmacological activity, but it is restricted by further applications by the difficulty in preparation. In this study, deep eutectic solvent (DES)-based aqueous two-phase system (ATPS) was established to transform and extract ginsenoside CK in situ for the first time. The phase formation conditions for preparing ATPS using choline chloride-based DES were studied, and the optimal conditions for extractive bioconversion were explored using conventional single-factor experiments. The conditions for ATPS establishment were as follows: 31.9% (w/w) DES (ChCl-ethylene glycol)/24.5% (w/w) K₂HPO₄, 55 °C, pH 5.0. Under the optimal conditions, 75.79% product and 61.14% β-glucosidase were recovered from the top and bottom phase, respectively. In addition, DES and β-glucosidase can be recovered and recycled again for the next extractive bioconversion of CK. These results indicated that this green and efficient method exhibited considerable value in integrated production and extraction processes, and demonstrated the potential for obtaining highly recycled functional foods and similar products.

Biocatalytic production of compound K in a deep eutectic solvent based on choline chloride using a substrate fed-batch strategy

This study involved the development of a β-glucosidase-catalyzed hydrolysis method based on a deep eutectic solvent (DES), choline chloride-ethylene glycol 2:1, and continuous feed technique to overcome the difficulty of high-concentration ginsenoside hydrolysis. A productivity of 142 mg·L-1·h-1 was achieved with the following conditions: 30 vol% DES, pH 5.0, 55 °C, and substrate concentration of 12 mM. In the presence of DES, the affinity and catalytic efficiency of β-glucosidase to Rd increased by 49 and 64%, respectively, which promoted the continuation of hydrolysis. Moreover, conformation of β-glucosidase was mostly retained, as confirmed by spectral information. Through a combination of a substrate fed-batch technique to reduce the inhibitory effects of substrates and products, the CK conversion rate increased by 44% compared to traditional single-batch in pure buffer. This report describes a practical method for the continuous conversion of natural compounds through biological processes and solvent engineering.

Immobilization of laccase on magnetically separable biochar for highly efficient removal of bisphenol A in water

Laccase was stably immobilized on a cost effective and nanosized magnetic biochar (L-MBC) by adsorption, precipitation and crosslinking, and it was used for high performance BPA removal. A large amount of enzyme could be immobilized on the magnetic biochar with high activity (2.251 U per mg MBC), and the L-MBC could be magnetically separated from the aqueous solution in 20 seconds. The successful immobilization of laccase was also confirmed via FTIR, SEM, and EDS analyses. The L-MBC presented better storage and stability performances, pH tolerance and thermal stability than the free laccase. It was found that BPA with an initial concentration of 25 mg L-1 could be thoroughly removed within 75 min, where BPA removal was attributed to enzymatic degradation and adsorption. In addition, the BPA removal efficiency by the L-MBC could be maintained above 85% even after seven cycles of repeated use. Due to high stability and efficient recyclability, the L-MBC-based biocatalyst has the potential to be a reliable method for treating BPA in environmental water sources.