Biocatalytic synthesis of short-chain flavor esters with high substrate loading by a whole-cell lipase from Aspergillus oryzae

Highly enantioselective resolution of racemic 1-phenyl-1,2-ethanediol to (S)-1-phenyl-1,2-ethanediol by Kurthia gibsonii SC0312 in a biphasic system

The asymmetric resolution of racemic 1-phenyl-1,2-ethanediol (PED) to (S)-PED by Kurthia gibsonii SC0312 (K. gibsonii SC0312) was conducted in a biphasic system comprised of an organic solvent and aqueous phosphate buffer. The impacts of organic solvents on the whole cell catalytic activity, metabolic activity, membrane integrity, and material distribution were first evaluated. The results showed that all organic solvents, except for dibutyl phthalate, showed a detrimental effect on the metabolic activity of the cells, especially for those with low log P values. All organic solvents were capable of changing the membrane permeability and membrane integrity of the cells. Moreover, some organic solvents showed a good extraction of the oxidation product. Finally, a high yield of 47.7 % of (S)-PED was obtained by the asymmetric resolution of racemic PED using K. gibsonii SC0312 in a biphasic system under the optimal conditions: racemic PED 120 mM, temperature 35 °C, reaction time 6 h, 180 rpm, and a volume ratio of dibutyl phthalate to aqueous phosphate buffer of 1:1. The optical purity of (S)-PED increased from 51.3 % to >99 %. This work described an efficient approach to improve reaction efficiency, and constructed a highly effective biphasic reaction system for the fabrication of (S)-PED via K. gibsonii SC0312.

One-pot lipase-catalyzed esterification of ε-caprolactone with methyl-d-glucopyranoside and its elongation with free 6-hydroxyhexanoate monomer units

One-pot synthesis of sugar-functionalized oligomeric caprolactone was carried out by lipase-catalyzed esterification of ε-caprolactone (ECL) with methyl-d-glucopyranoside (MGP) followed by the elongation of functionalized oligomer chain. Functionalization was performed in a custom-fabricated glass reactor equipped with Rushton turbine impeller and controlled temperature at 60 °C using tert-butanol as reaction medium. The overall reaction steps include MGP esterification of ECL monomer and its subsequent elongation by free 6-hydroxyhexanoate monomer units. A ping-pong bi-bi mechanism without ternary complex was proposed for esterification of ECL and MGP with apparent values of kinetic constant, namely maximal velocity (V_max ), Michaelis constant for MGP (K_mMGP ), and Michaelis constant for ECL (K_mECL ) at 3.848 × 10^-3  M H^-1 , 8.189 × 10^-2  M, and 6.050 M, respectively. Chain propagation step of MGP-functionalized ECL oligomer exhibits the properties of living polymerization mechanism. Linear relationship between conversion (%) and number average molecular weight, M_n (g mol^-1 ), of functionalized oligomer was observed. Synthesized functionalized oligomer showed narrow range of molecular weight from 1,400 to 1,600 g mol^-1 with more than 90% conversion achieved. Structural analysis confirmed the presence of covalent bond between the hydroxyl group in MGP with carboxyl end group of ECL oligomer.

Surfactant-modified Aspergillus oryzae lipase as a highly active and enantioselective catalyst for the kinetic resolution of (RS)-1-phenylethanol

The lipase from Aspergillus oryzae was modified with a surfactant and then observed to exhibit high catalytic efficiency and enantioselectivity for the kinetic resolution of (RS)-1-phenylethanol. The influential factors of the modified-lipase preparation were investigated, including the surfactant source, the organic cosolvent, and the buffer pH. The optimum modification conditions were found with a surfactant of polyoxyethylene sorbitan monopalmitate, an organic cosolvent of tetrahydrofuran and a phosphate buffer of pH 7.0. In the transesterification of (RS)-1-phenylethanol with vinyl acetate, the surfactant-modified lipase showed excellent enantioselectivity for the R-isomer (E > 200), giving an enantiomeric excess of higher than 99% for (R)-1-phenylethyl acetate at 46.8% conversion with the reaction time of 2 h at 30 °C. The enzymatic activity had barely altered after 30 days even at 50 °C when it was saved in a powdered state. The results indicated that the modification strategy was useful and highly efficient, and that modified A. oryzae lipase was a promising biocatalyst in the kinetic resolution of (RS)-1-phenylethanol.

High-level expression and characterization of a stereoselective lipase from Aspergillus oryzae in Pichia pastoris

Pichia pastoris expression is a mature and efficient eukaryotic expression system. In this work, Aspergillus oryzae lipase (AOL, with the molecular mass of 28 kDa), which can perform highly stereoselective hydrolysis of (R, S)-methyl 2-(4-hydroxyphenoxy) propanoate, was expressed in P. pastoris X-33. The specific activity of AOL was 432 U/mg, which was obtained by fed-batch cultivation in a 5 L bioreactor using a methanol feeding strategy. After fermentation, the supernatant was concentrated by ultrafiltration with a 10 kDa cut-off membrane and purified with DEAE-Sepharose™ FF ion-exchange chromatography and phenyl Seflnose™ 6 FF hydrophobic interaction chromatography. The purified lipase activity reached 5509 U/mg. AOL showed high activity toward short-chain triacylglyceride (C₄), and the optimum temperature and pH were 40 °C and 8.0, respectively. The purified enzyme activity was inhibited by Zn²⁺ and Cu²⁺. Moreover, the K_m and V_max values were 1 mM and 32.89 mmol/min, respectively.

Exquisite stability and catalytic performance of immobilized lipase on novel fabricated nanocellulose fused polypyrrole/graphene oxide nanocomposite: Characterization and application

This work was performed to describe the facile procedure of a novel nanobiocatalyst, nano cellulose fused polypyrrole/graphene oxide nanocomposite for the efficacious immobilization of lipase, a versatile hydrolytic enzyme having potential applications in industries. The fabricated nanocomposite was characterized using Fourier transform infrared spectroscopy, differential thermal analysis, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, atomic force microscopy, transmission electron microscopy, and Candida rugosa lipase was immobilized onto nanocomposite through physical adsorption. The catalytic efficiency and operational stabilities of immobilized lipase were improved significantly compared to the free lipase. The reusability profile outcomes showed that the immobilized lipase formulation was an outstanding nanobiocatalyst as it retained 85% of its original catalytic activity after 10 cycles of application. The nanobiocatalyst was employed for the synthesis of the fruit flavour compound, ethyl acetoacetate. The immobilized lipase successfully synthesised flavour compound in solvent free media and n-hexane having 27.5% and 75.5% ester yields respectively. Moreover, these outcomes demonstrating graphene oxide modified carrier induced stabilization, amended solvent tolerance and operational stability of immobilized enzyme, will have quintessential influence on practical scale up of biotechnological industries.

Studies on the catalytic behavior of a membrane-bound lipolytic enzyme from the microalgae Nannochloropsis oceanica CCMP1779

The catalytic behavior of a membrane-bound lipolytic enzyme (MBL-Enzyme) from the microalgae Nannochloropsis oceanica CCMP1779 was investigated. The biocatalyst showed maximum activity at 50 °C and pH 7.0, and was stable at pH 7.0 and temperatures from 40 to 60 °C. Half-lives at 60 °C, 70 °C and 80 °C were found 866.38, 150.67 and 85.57 min respectively. Thermal deactivation energy was 68.87 kJ mol^-1. The enzyme's enthalpy (ΔΗ*), entropy (ΔS*) and Gibb's free energy (ΔG*) were in the range of 65.86-66.27 kJ mol^-1, 132.38-140.64 J mol^-1 K^-1 and 107.80-115.81 kJ mol^-1, respectively. Among p-nitrophenyl esters of fatty acids tested, MBL-Enzyme exhibited the highest hydrolytic activity against p-nitrophenyl palmitate (pNPP). The K_m and V_max values were found 0.051 mM and of 0.054 mmole pNP mg protein^-1 min^-1, respectively with pNPP as substrate. The presence of Mn²⁺ increased lipolytic activity by 68.25%, while Fe³⁺ and Cu²⁺ ions had the strongest inhibitory effect. MBL-Enzyme was stable in the presence of water miscible (66% of the initial activity in ethanol) and water immiscible (71% of the initial activity in n-octane) solvents. Myristic acid was found to be the most efficient acyl donor in esterification reactions with ethanol. Methanol was the best acyl acceptor among the primary alcohols tested.

Immobilization of a Cutinase from Fusarium oxysporum and Application in Pineapple Flavor Synthesis

In the present study, the immobilization of a cutinase from Fusarium oxysporum was carried out as cross-linked enzyme aggregates. Under optimal immobilization conditions, acetonitrile was selected as precipitant, utilizing 9.4 mg protein/mL and 10 mM glutaraldehyde as cross-linker. The immobilized cutinase (imFocut5a) was tested in isooctane for the synthesis of short-chain butyrate esters, displaying enhanced thermostability compared to the free enzyme. Pineapple flavor (butyl butyrate) synthesis was optimized, leading to a conversion yield of >99% after 6 h, with an initial reaction rate of 18.2 mmol/L/h. Optimal reaction conditions were found to be 50 °C, a vinyl butyrate/butanol molar ratio of 3:1, vinyl butyrate concentration of 100 mM, and enzyme loading of 11 U. Reusability studies of imFocut5a showed that after four consecutive runs, the reaction yield reaches 54% of the maximum. The efficient bioconversion offers a sustainable and environmentally friendly process for the production of "natural" aroma compounds essential for the food industry.

Genome mining of fungal lipid-degrading enzymes for industrial applications

Lipases are interesting enzymes, which contribute important roles in maintaining lipid homeostasis and cellular metabolisms. Using available genome data, seven lipase families of oleaginous and non-oleaginous yeast and fungi were categorized based on the similarity of their amino acid sequences and conserved structural domains. Of them, triacylglycerol lipase (patatin-domain-containing protein) and steryl ester hydrolase (abhydro_lipase-domain-containing protein) families were ubiquitous enzymes found in all species studied. The two essential lipases rendered signature characteristics of integral membrane proteins that might be targeted to lipid monolayer particles. At least one of the extracellular lipase families existed in each species of yeast and fungi. We found that the diversity of lipase families and the number of genes in individual families of oleaginous strains were greater than those identified in non-oleaginous species, which might play a role in nutrient acquisition from surrounding hydrophobic substrates and attribute to their obese phenotype. The gene/enzyme catalogue and relevant informative data of the lipases provided by this study are not only valuable toolboxes for investigation of the biological role of these lipases, but also convey potential in various industrial applications.

Immobilization, Regiospecificity Characterization and Application of Aspergillus oryzae Lipase in the Enzymatic Synthesis of the Structured Lipid 1,3-Dioleoyl-2-Palmitoylglycerol

The enzymatic synthesis of 1,3-dioleoyl-2-palmitoylglycerol (OPO), one of the main components of human milk fats, has been hindered by the relatively high cost of sn-1,3-specific lipases and the deficiency in biocatalyst stability. The sn-1,3-specific lipase from Aspergillus oryzae (AOL) is highly and efficiently immobilized with the polystyrene-based hydrophobic resin D3520, with a significant 49.54-fold increase in specific lipase activity compared with the AOL powder in catalyzing the synthesis of OPO through the acidolysis between palm stearin and oleic acid (OA). The optimal immobilization conditions were investigated, including time course, initial protein concentration and solution pH. The sn-1,3 specificity of lipases under different immobilization conditions was evaluated and identified as positively associated with the lipase activity, and the pH of the immobilization solution influenced the regiospecificity and synthetic activity of these lipases. Immobilized AOL D3520, as the biocatalyst, was used for the enzymatic synthesis of the structured lipid OPO through the acidolysis between palm stearin and OA. The following conditions were optimized for the synthesis of structured lipid OPO: 65 °C temperature; 1:8 substrate molar ratio between palm stearin and OA; 8% (w/w) enzyme load; 3.5% water content of the immobilized lipase; and 1 h reaction time. Under these conditions, highly efficient C52 production (45.65%) was achieved, with a tripalmitin content of 2.75% and a sn-2 palmitic acid (PA) proportion of 55.08% in the system.