Water activity dependence of lipase catalysis in organic media explains successful transesterification reactions

Synthesis of a Lignin-Enhanced Graphene Aerogel for Lipase Immobilization

A novel lignin-enhanced graphene aerogel (LGA) was prepared by one-step hydrothermal synthesis, and lipase from Pseudomonas sp. (PSL) was immobilized on LGA successfully by interfacial activation. The catalytic activity and enantioselectivity of LGA-PSL for the preparation of (S)-2-octanol by an enantioselective transesterification were improved obviously. The characterization of LGA and LGA-PSL was performed. X-ray diffraction and Fourier transform infrared spectroscopy demonstrated the formation of numerous electrostatic and hydrogen bonds between lignin and graphene in the aerogel structure. In addition, the specific surface area pore size analyzer (BET) test proved that the introduction of lignin significantly increased the specific surface area and pore size of the aerogel material, which improved the immobilization efficiency of lipase in the aerogel. The introduction of lignin has changed the original lamellar structure of the graphene oxide (GO) aerogels. The lignin cross-linked with the GO lamellae through hydrogen bonding, causing a porous structure to form between the original lamellae, thus increasing their specific surface area. The immobilized lipase (LGA-PSL) was used for the preparation of (S)-2-octanol by an enantioselective transesterification, and the reaction conditions for this enzymatic transesterification had been optimized. LGA-PSL exhibited a high catalytic performance and could be reused four times in this reaction. Based on these results, LGA as an immobilization carrier had potential applications in the industrial application of lipase.

Progress in enrichment of n-3 polyunsaturated fatty acid: a review

n-3 Polyunsaturated fatty acids (n-3 PUFA) has been widely used in foods, and pharmaceutical products due to its beneficial effects. The content of n-3 PUFA in natural oils is usually low, which decreases its added value. Thus, there is an increasing demand on the market for n-3 PUFA concentrates. This review firstly introduces the differences in bioavailability and oxidative stability between different types of PUFA concentrate (free fatty acid, ethyl ester and acylglycerol), and then provides a comprehensive discussion of different methods for enrichment of lipids with n-3 PUFA including physical-chemical methods and enzymatic methods. Lipases used for catalyzing esterification, transesterification and hydrolysis reactions play an important role in the production of highly enriched various types of n-3 PUFA concentrates. Lipase-catalyzed alcoholysis or hydrolysis reactions are the mostly employed method to prepare high-quality n-3 PUFA of structural acylglycerols. Although many important advantages offered by lipases in enrichment of n-3 PUFA, the high cost of enzyme limits its industrial-scale production. Further research should focus on looking for biological enzymes with extraordinary catalytic ability and clear selectivity. Other novel technologies such as protein engineering and immobilization may be needed to modify lipases to improve its selectivity, catalytic ability and reuse.

Investigation of effect of ultrasound on immobilized C. rugosa lipase: Synthesis of biomass based furfuryl derivative and green metrics evaluation study

The present work deals with the synthesis of lab-made carboxymethyl cellulose (CMC) and chitosan (CHI) based co-polymer cross-linked with glutaraldehyde (GLU) which is used as immobilization matrix for the immobilization of Candida rugosa (CRL) lipase (CMC:CHI:GLU:CRL). This immobilized biocatalyst was subjected to characterization such as lipase-activity, kinetic-parameters, water-content, surface-texture, stability and half-life time etc. Effect of various ultrasound parameters (power, frequency, duty cycle, exposure time) on lipase activity is also tested which indicated that, developed biocatalyst has significant activity-stability and half-life-time in ultrasonicated medium. Further, this biocatalyst was applied to synthesize biomass-derived furfuryl derivative which offering excellent conversion of 99 % of bio-based furfuryl ester. The synthetic protocol is optimized in detail (with twelve reaction parameters) under ultrasonicated medium. Recyclability study offered 68 % conversion of the furfuryl ester after sixth reuse. Moreover, the developed protocol is well extended to synthesize various commercially important compounds. Besides this, we investigated thermodynamic parameters (ΔG*, ΔH*, ΔS*) which demonstrating more feasibility of biocatalytic synthesis in ultrasonicated medium than conventional medium. Finally, green metrics evaluation parameters (E-factor, carbon-efficiency and mass-intensity) are studied which indicating efficient synergetic role of immobilized CMC:CHI:GLU:CRL lipase biocatalysis and ultrasonication in green and sustainable synthesis.

Synthesis of propyl benzoate by solvent-free immobilized lipase-catalyzed transesterification: Optimization and kinetic modeling

The present study aimed to analyze reaction kinetics and mechanism for the synthesis of propyl benzoate in solvent-free conditions. Lipase was immobilized on Hydroxypropyl methylcellulose (HPMC) and polyvinyl alcohol (PVA) polymer blend by entrapment method. Among different lipases immobilized on a support, Candida cylindracea (CCL) showed excellent activity. Systematic studies were done to optimize the reaction conditions. The activation energy was found to be 16.2 kcal/mol for immobilized CCL. Kinetic parameters were calculated, which depicted that propyl benzoate synthesized using immobilized CCL followed the ternary complex model in which propanol inhibits lipase activity at higher concentrations. Recyclability of the catalyst was checked up to four catalytic cycles and 40% retention of activity was observed up to the fourth cycle. Finally, the applicability of developed protocol to synthesize various alkyl benzoates was explored.

Bacillus subtilis Lipase A—Lipase or Esterase?

The question of how to distinguish between lipases and esterases is about as old as the definition of the subclassification is. Many different criteria have been proposed to this end, all indicative but not decisive. Here, the activity of lipases in dry organic solvents as a criterion is probed on a minimal α/β hydrolase fold enzyme, the Bacillus subtilis lipase A (BSLA), and compared to Candida antarctica lipase B (CALB), a proven lipase. Both hydrolases show activity in dry solvents and this proves BSLA to be a lipase. Overall, this demonstrates the value of this additional parameter to distinguish between lipases and esterases. Lipases tend to be active in dry organic solvents, while esterases are not active under these circumstances.

Lipase Catalyzed Acidolysis for Efficient Synthesis of Phospholipids Enriched with Isomerically Pure cis-9,trans-11 and trans-10,cis-12 Conjugated Linoleic Acid

The production of phospholipid (PL) conjugates with biologically active compounds is nowadays an extensively employed approach. This type of phospholipids conjugates could improve bioavailability of many poorly absorbed active compounds such as isomers of conjugated linoleic acid (CLA), which exhibit versatile biological effects. The studies were carried out to elaborate an efficient enzymatic method for the synthesis of phospholipids with pure (>90%) cis-9,trans-11 and trans-10,cis-12 CLA isomers. For this purpose, three commercially available immobilized lipases were examined in respect to specificity towards CLA isomers in acidolysis of egg-yolk phosphatidylcholine (PC). Different incorporation rates were observed for the individual CLA isomers. Under optimal conditions: PC/CLA molar ratio 1:6; Rhizomucor miehei lipase loading 24% wt. based on substrates; heptane; DMF, 5% (v/v); water activity (aw), 0.11; 45 °C; magnetic stirring, 300 rpm; 48 h., effective incorporation (EINC) of CLA isomers into PC reached ca. 50%. The EINC of CLA isomers was elevated for 25–30% only by adding a water mimic (DMF) and reducing aw to 0.11 comparing to the reaction system performed at aw = 0.23. The developed method of phosphatidylcholine acidolysis is the first described in the literature dealing with isometrically pure CLA and allow to obtain very high effective incorporation.

Optimization of solvent-free enzymatic esterification in eutectic substrate reaction mixture

The Candida rugosa lipase catalyzed esterification of (-)-menthol and lauric acid (LA) was studied in a eutectic mixture formed by both substrates((-)-menthol:LA 3:1, mol/mol). No additional reaction solvent was necessary, since the (-)-menthol:LA deep eutectic solvent (DES) acts as combined reaction medium and substrate pool. Therefore, the esterification is conducted under solvent-free conditions. The thermodynamic water activity (a_w) was identified as a key parameter affecting the esterification performance in the (-)-menthol:LA DES. A response surface methodology was applied to optimize the esterification conditions in terms a_w, amount of C. rugosa lipase (m_CRL) and reaction temperature. Under the optimized reaction conditions (a_w = 0.55; m_CRL =60 mg; T =45 °C), a conversion of 95 ± 1% LA was achieved (one day), the final (-)-menthyl lauric acid ester concentration reached 1.36 ± 0.04 M (2.25 days). The experimental product formation rate agreed very well with the model prediction.

Comparison of lipases and glycoside hydrolases as catalysts in synthesis reactions

Lipases and glycoside hydrolases have large similarities concerning reaction mechanisms. Acyl-enzyme intermediates are formed during lipase-catalyzed reactions and in an analogous way, retaining glycoside hydrolases form glycosyl-enzyme intermediates during catalysis. In both cases, the covalent enzyme intermediates can react with water or other nucleophiles containing hydroxyl groups. Simple alcohols are accepted as nucleophiles by both types of enzymes. Lipases are used very successfully in synthesis applications due to their efficiency in catalyzing reversed hydrolysis and transesterification reactions. On the other hand, synthesis applications of glycoside hydrolases are much less developed. Here, important similarities and differences between the enzyme groups are reviewed and approaches to reach high synthesis yields are discussed. Useful strategies include the use of low-water media, high nucleophile concentrations, as well as protein engineering to modify the selectivity of the enzymes. The transglycosylases, hydrolases which naturally catalyze mainly transfer reactions, are of special interest and might be useful guides for engineering of other hydrolases.

Scaling-up the synthesis of myristate glucose ester catalyzed by a CALB-displaying Pichia pastoris whole-cell biocatalyst

The novel whole-cell biocatalyst Candida antarctica lipase B displaying-Pichia pastoris (Pp-CALB) is characterized by its low preparation cost and could be an alternative to the commercial immobilized Candida antarctica lipase B (CALB). This study addresses the feasibility of using Pp-CALB in large scale glucose fatty acid esters production. 1,2-O-Isopropylidene-α-D-glucofuranose (IpGlc) was used as the acyl acceptor to overcome the low solubility of glucose in an organic solvent and to avoid the addition of toxic co-solvents. IpGlc significantly improved the Pp-CALB catalyzing esterification efficiency when using long chain fatty acids as the acyl donor. Under the preferred operating conditions (50 °C, 40 g/L molecular sieve dosage and 200 rpm mixing intensity), 60.5% of IpGlc converted to 6-O-myristate-1, 2-O-isopropylidene-α-D-glucofuranose (C14-IpGlc) after a 96-h reaction in a 2-L stirred reactor. In a 5-L pilot scale test, Pp-CALB also showed a similar substrate conversion rate of 55.4% and excellent operational stability. After C14-IpGlc was collected, 70% trifluoroacetic acid was adopted to hydrolyze C14-IpGlc to myristate glucose ester (C14-Glc) with a high yield of 95.3%. In conclusion, Pp-CALB is a powerful biocatalyst available for industrial synthesis, and this study describes an applicable and economical process for the large scale production of myristate glucose ester.

Methods for improving enzymatic trans-glycosylation for synthesis of human milk oligosaccharide biomimetics

Recently, significant progress has been made within enzymatic synthesis of biomimetic, functional glycans, including, for example, human milk oligosaccharides. These compounds are mainly composed of N-acetylglucosamine, fucose, sialic acid, galactose, and glucose, and their controlled enzymatic synthesis is a novel field of research in advanced food ingredient chemistry, involving the use of rare enzymes, which have until now mainly been studied for their biochemical significance, not for targeted biosynthesis applications. For the enzymatic synthesis of biofunctional glycans reaction parameter optimization to promote "reverse" catalysis with glycosidases is currently preferred over the use of glycosyl transferases. Numerous methods exist for minimizing the undesirable glycosidase-catalyzed hydrolysis and for improving the trans-glycosylation yields. This review provides an overview of the approaches and data available concerning optimization of enzymatic trans-glycosylation for novel synthesis of complex bioactive carbohydrates using sialidases, α-l-fucosidases, and β-galactosidases as examples. The use of an adequately high acceptor/donor ratio, reaction time control, continuous product removal, enzyme recycling, and/or the use of cosolvents may significantly improve trans-glycosylation and biocatalytic productivity of the enzymatic reactions. Protein engineering is also a promising technique for obtaining high trans-glycosylation yields, and proof-of-concept for reversing sialidase activity to trans-sialidase action has been established. However, the protein engineering route currently requires significant research efforts in each case because the structure-function relationship of the enzymes is presently poorly understood.

Homologous yeast lipases/acyltransferases exhibit remarkable cold-active properties

Lipases/acyltransferases catalyse acyltransfer to various nucleophiles preferentially to hydrolysis even in aqueous media with high thermodynamic activity of water (a w >0.9). Characterization of hydrolysis and acyltransfer activities in a large range of temperature (5 to 80 °C) of secreted recombinant homologous lipases of the Pseudozyma antarctica lipase A superfamily (CaLA) expressed in Pichia pastoris, enlighten the exceptional cold-activity of two remarkable lipases/acyltransferases: CpLIP2 from Candida parapsilosis and CtroL4 from Candida tropicalis. The activation energy of the reactions catalysed by CpLIP2 and CtroL4 was 18-23 kJ mol(-1) for hydrolysis and less than 15 kJ mol(-1) for transesterification between 5 and 35 °C, while it was respectively 43 and 47 kJ mol(-1) with the thermostable CaLA. A remarkable consequence is the high rate of the reactions catalysed by CpLIP2 and CtroL4 at very low temperatures, with CpLIP2 displaying at 5 °C 65 % of its alcoholysis activity and 45 % of its hydrolysis activity at 30 °C. These results suggest that, within the CaLA superfamily and its homologous subgroups, common structural determinants might allow both acyltransfer and cold-active properties. Such biocatalysts are of great interest for the efficient synthesis or functionalization of temperature-sensitive lipid derivatives, or more generally to lessen the environmental impact of biocatalytic processes.

Activation of immobilized lipase in non-aqueous systems by hydrophobic poly-DL-tryptophan tethers

Many industrially important reactions use immobilized enzymes in non-aqueous, organic systems, particularly for the production of chiral compounds such as pharmaceutical precursors. The addition of a spacer molecule ("tether") between a supporting surface and enzyme often substantially improves the activity and stability of enzymes in aqueous solution. Most "long" linkers (e.g., polyethylene oxide derivatives) are relatively hydrophilic, improving the solubility of the linker-enzyme conjugate in polar environments, but this provides little benefit in non-polar environments such as organic solvents. We present a novel method for the covalent immobilization of enzymes on solid surfaces using a long, hydrophobic polytryptophan tether. Candida antarctica lipase B (CALB) was covalently immobilized on non-porous, functionalized 1-microm silica microspheres, with and without an intervening hydrophobic poly-DL-tryptophan tether (n approximately 78). The polytryptophan-tethered enzyme exhibited 35 times greater esterification of n-propanol with lauric acid in the organic phase and five times the hydrolytic activity against p-nitrophenol palmitate, compared to the activity of the same enzyme immobilized without tethers. In addition, the hydrophobic tethers caused the silica microspheres to disperse more readily in the organic phase, while the surface-immobilized control treatment was less lipophilic and quickly settled out of the organic phase when the suspensions were not vigorously mixed.

The lipase-catalyzed hydrolysis of lutein diesters in non-aqueous media is favored at extremely low water activities

The enzymatic hydrolysis of a mixture of lutein diesters from Marigold flower (Tagetes erecta) was performed both in organic solvents and supercritical CO(2) (SC-CO(2)) using two commercial lipases: lipase B from Candida antarctica (Novozym 435) and the lipase from Mucor miehei (Lipozyme RM IM). Both lipases showed an unexpected dependence of initial reaction rate with the initial water activity (a(wi)) in hexane, with the highest rates of hydrolysis taking place at the lowest a(wi) of the biocatalyst particles. The same result was observed using isooctane, toluene, or SC-CO(2). It is proposed that an increase in a(wi) generates a hydrophilic microenvironment that prevents efficient partitioning of the highly hydrophobic lutein diesters to the enzyme. The critical role of water in this system has not been reported for other hydrolytic reactions in low water media. Calculations of water available for hydrolysis from isotherm analysis, Karl-Fischer titration, and substrate conversion at a(wi) = 0.13, indicate that the extent of reaction is not limited by the amount of available water. Accordingly, the enzyme that holds the largest amount of water after prehydration at the same a(wi) (0.13) will yield the greatest substrate conversion and concentration of the free lutein product. The highest conversion occurred in SC-CO(2), which opens up new opportunities to develop a combined extraction-reaction process for the environmentally benign synthesis of lutein, an important nutraceutical compound.