Lipase-mediated synthesis of dodecyl oleate and oleyl oleate in aqueous foams

Engineering media for optimal product yield in enzyme-catalyzed reactions is an important strategy. We report here synthesis of dodecyl oleate and oleyl oleate by lipase (Candida rugosa) in solvent-free substrate foams. Ester formation was characterized with respect to enzyme concentration, pH, temperature, and substrate concentration. The kinetics of ester formation suggest that the formation of ester was 80% complete in 2h. The pH and temperature optima of lipase suggest that the behavior of lipase in substrate foams was similar to its behavior in water or in organic solvents. The denaturing effect of foams on enzyme was evaluated. Rapid loss in activity (>70% in 1 h) was observed in the presence of oleic acid and dodecanol. The large surface areas generated in aqueous foams offer better accessibility of substrate to lipase for esterification.     

Lipase-catalyzed esterification of glycerol and oleic acid

The enzymatic synthesis of glycerides from glycerol and oleic acid in organic solvent was studied, and the optimal conditions for glyceride synthesis by lipases were established. Of the commercially available lipases that were investigated, Candida rugosa lipase and porcine pancreas lipase resulted in the highest extent of esterification. Iso-octane and hexane were particularly useful organic solvents in glyceride synthesis. The water content in the reaction mixture was of primary importance. For C. rugosa lipase and porcine pancreas lipase, the optimal water contents were 5 and 1%, respectively. Candida rugosa lipase and porcine pancreas lipase manifested contrasting positional specificities in glyceride synthesis.     

Enzymatic and chemical synthesis of phosphatidylcholine regioisomers containing eicosapentaenoic acid or docosahexaenoic acid

Regioselective incorporation of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) into phosphatidylcholine (PC) was carried out using enzymatic and chemical synthesis. Incorporation at the sn‐1 position was successfully achieved by lipase‐catalysed esterification of 2‐palmitoyl‐lysophosphatidylcholine (LPC), although in most cases, the enzymes incorporated EPA and DHA at lower rates than other fatty acids. For the incorporation of DHA, Candida antarctica lipase B was the only useful enzyme, while incorporation of EPA was efficiently carried out using either this enzyme or Rhizopus arrhizus lipase. The highest yields in the lipase‐catalysed reactions were obtained at the lowest water activity (close to 0). However, by carrying out the reactions at a higher water activity of 0.22, more EPA and DHA were incorporated. Esterification of 2‐palmitoyl‐LPC with pure EPA at this water activity converted 66 mol‐% of LPC to PC using Rhizopus arrhizus lipase as catalyst. When the fatty acid was DHA and the catalyst Candida antarctica lipase B, 45 mol‐% of PC was obtained. For incorporation of EPA and DHA at the sn‐2 position, phospholipase A₂ was used, but the reaction was very slow. Chemical coupling of 1‐palmitoyl‐LPC and EPA or DHA was more efficient, resulting in complete conversion of LPC.     

Stability of Immobilized Candida sp. 99–125 Lipase for Biodiesel Production

The stability of the immobilized lipase from Candida sp. 99–125 during biodiesel production was investigated. The lipase was separately incubated in the presence of various reaction components such as soybean oil, oleic acid methyl ester, n‐hexane, water, methanol, and glycerol, or the lipase was stored at 60, 80, 100 and 120 °C. Thereafter the residual lipase activity was determined by methanolysis reaction. The results showed that the lipase was rather stable in the reaction media, except for methanol and glycerol. The stability study performed in a reciprocal shaker indicated that enzyme desorption from the immobilized lipase mainly contributed to the lipase inactivation in the water system. So the methanol and glycerol contents should be controlled more precisely to avoid lipase inactivation, and the immobilization method should be improved with regard to lipase desorption.     

Enzymatic fatty ester synthesis

Fatty ester synthesis with immobilized 1,3-specific lipase fromMucor miehei is described. 1,2-Isopropylidene glycerol produced by condensation of glycerol with acetone was esterified with oleic acid in the presence of aMucor miehei lipase (Lipozyme™) to obtain 1,2-isopropylidene-3-oleoyl glycerol. The effects of various process parameters (temperature and pressure) and various ratios (enzyme/substrate) have been investigated to determine optimal conditions for the esterification process. The highest conversion of oleic acid (80% w/w) was obtained at 55°C and 0.057 bar, while the optimal addition of lipase to substrate was determined to be 0.096 g per gram of reaction mixture. The esterification can be modeled successfully as a reverse second-order reaction. Thermodynamic properties of the reaction system at 55°C and 0.057 bar also were determined. Activation energy was 20.82 kJ/mole, entropy of activation −0,26 kJ/(K mole) and free energy of activation was 103.32 kJ/mole.     

Enzymatic Production of Fatty Acid Methyl Esters by Hydrolysis of Acid Oil Followed by Esterification

Acid oil, a by-product of vegetable oil refining, was enzymatically converted to fatty acid methyl esters (FAME). Acid oil contained free fatty acids (FFA), acylglycerols, and lipophilic compounds. First, acylglycerols (11 wt%) were hydrolyzed at 30 °C by 20 units Candida rugosa lipase/g-mixture with 40 wt% water. The resulting oil layer containing 92 wt% FFA was used for the next reaction, methyl esterification of FFA to FAME by immobilized Candida antarctica lipase. A mixture of 66 wt% oil layer and 34 wt% methanol (5 mol for FFA) were shaken at 30 °C with 1.0 wt% lipase. The degree of esterification reached 96% after 24 h. The resulting reaction mixture was then dehydrated and subjected to the second esterification that was conducted with 2.2 wt% methanol (5 mol for residual FFA) and 1.0 wt% immobilized lipase. The degree of esterification of residual FFA reached 44%. The degree increased successfully to 72% (total degree of esterification 99%) by conducting the reaction in the presence of 10 wt% glycerol, because water in the oil layer was attracted to the glycerol layer. Over 98% of total esterification was maintained, even though the first and the second esterification reactions were repeated every 24 h for 40 days. The enzymatic process comprising hydrolysis and methyl esterification produced an oil containing 91 wt% FAME, 1 wt% FFA, 1 wt% acylglycerols, and 7 wt% lipophilic compounds.     

Effect of light irradiation on esterification of oleic acid with ethanol catalyzed by immobilized Pseudomonas cepacia lipase

The present study demonstrates the effect of light irradiation on the esterification of oleic acid catalyzed by immobilized Pseudomonas cepacia lipase. The reaction rates of all the experiments under light irradiation were found to be higher than dark conditions. The kinetics of reactions supported the Ping‐Pong Bi‐Bi mechanism with dead end inhibition by both the alcohol and acid substrates. Moreover, circular dichroism (CD) spectroscopy was used to analyze the effect of light on lipase enzyme. The CD spectroscopic studies confirmed that the conformational changes in the secondary structure of the lipase enzyme increased the reaction rate of light‐illuminated experiments, which might have opened up the active sites of enzymes and thus, resulted in higher reaction rates compared to dark reactions. These results have successfully demonstrated that the light illumination positively influenced the rate of P. cepacia enzyme‐catalyzed esterification reactions.     

Kinetic studies of Mucor miehei lipase in phosphatidylcholine microemulsions

Ethanol—oleic acid esterification by a free and microencapsulated lipase from Mucor miehei, using dodecane as solvent and phosphatidylcholine as surfactant, was studied. The initial esterification rate was influenced by the water content in the biphasic system. Kinetic studies with free and microencapsulated enzyme showed that the microencapsulation led to an increase of the kinetic parameters (V_max and K_m), probably due to an increase of the interfacial area. The reaction rate was also affected by the shaking rate, the temperature and the pH. The optimal temperature and pH achieved were, respectively, 40°C and 4.5 using free enzyme, and 50°C and 6 using microencapsulated enzyme.     

Optimisation of the enzymatic synthesis of n‐octyl oleate with immobilised lipase in the absence of solvents

The enzymatic synthesis of n‐octyl oleate by direct esterification of the oleic acid and the octanol in a solvent‐free medium was previously shown to be efficiently catalysed by a lipase from Rhizomucor miehei covalently linked to a graft copolymer, the partially hydrolysed poly(ethylene)‐g co‐hydroxyethyl methacrylate (PE‐g co‐HEMA). In this work we went further towards an optimisation of the production of n‐octyl oleate taking into account several parameters that affect the catalytic activity of the preparation. The physical characteristics of the support, such as the particle size and the degree of hydrolysis of the copolymer, the amount of lipase used in the method of immobilisation, the water content of the reaction mixture and the operational conditions of reaction, in particular the temperature, were evaluated in order to achieve not only high activities but also a good stability of the preparation. © 1999 Society of Chemical Industry     

Lipase‐catalysed esterification of oleic acid and ethanol in a continuous packed bed reactor,using supercritical CO2 as solvent: approximation of system kinetics

This work investigated the immobilised lipase kinetics of esterification of oleic acid and ethanol. The reaction was conducted under supercritical conditions (13 × 10⁶ Pa and 40 °C) using carbon dioxide as solvent in a continuous packed bed (plug flow) reactor. Biocatalyst Lypozyme^TM IM60, which is lipase from Rhizomucor miehei (EC.3.1.1.3), immobilised on Duolite (anionic exchange resin) was used as biocatalyst. Kinetically, with regard to oleic acid, the reaction was successfully modelled by the Michaelis–Menten mechanism. The reaction rate constants K_m and V_max were evaluated. Furthermore, it was found to undergo competitive inhibition by ethanol, and the inhibition constant K_i was evaluated. © 2000 Society of Chemical Industry     

Enzymatic production of fatty acid alkyl esters with a lipase preparation from Candida sp. 99‐125

A lipase preparation developed from Candida sp. 99‐125 was used for fatty acid alkyl ester synthesis by both enzymatic esterification of fatty acids, and transesterification of oils and fats. The lipase preparation was chosen based on screening of lipases from commercial sources as well as those produced in the laboratory. The effects of enzyme dosage, solvent types, water absorbent additions, inhibition of short‐chain alcohols, alcohol and acid types, molar ratio of substrates, and reusability of the lipase preparation in esterification were studied. Degree of esterification between oleic acid and methanol under optimal conditions reached 92%. Purity of the methyl ester after washing with water and distillation was 98%. Half‐life of the lipase preparation was calculated to be approximately 340 h. For transesterification of rapeseed oil with the same lipase preparation, the amount of methanol and mode of methanol addition to the reaction were also conducted. Transesterification of the oil with stepwise methanol addition reached 83% after 36 h reaction time.     

Investigation on the Esterification of Fatty Acids Catalyzed by the H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript> heteropolyacid

In this work, the H₃PW₁₂O₄₀ heteropolyacid (HPW) was employed as a homogeneous catalyst to promote the efficient esterification (ethanolysis) of a number of saturated and unsaturated fatty acids (myristic, palmitic, stearic, oleic, and linoleic) under mild reaction conditions. HPW showed a similar activity to those observed for p-toluene sulfonic acid (PTSA) and sulfuric acid (H₂SO₄), the other acidic catalysts we compared them with in this study. In the HPW-catalyzed esterification of stearic acid, the addition of water caused a remarkable decrease in the ethyl stearate yields. On the other hand, the increase in the HPW concentration (up to a maximum value) promoted a proportional improvement in the oleic acid to ethyl oleate conversion. Kinetic measurements using oleic acid as a prototype substrate revealed that the esterification reactions catalyzed by HPW, H₂SO₄, and PTSA are of first-order in relation to the fatty acid concentration. Finally, the catalytic activity of HPW remained unaltered even after several recovery/reutilization cycles whereas the tungsten content in the final product (biodiesel produced by the HPW-catalyzed esterification of oleic acid) was found to be at an acceptably low level (0.0095 mg of W per g of biodiesel).     

Use of lipases in multiphasic systems solely composed of substrates

Three lipase-catalyzed reactions have been investigated in relation to specificity and water dependence. The reactions in question include: the synthetic reaction between oleic acid and glycerol; the enzymatic hydrolysis of triolein; and alcoholysis/glycerolysis transesterification reactions. All reactions were carried out under solventfree conditions. In each case, the medium composition and reaction conditions were optimized in order to work at elevated substrate concentrations and to minimize the production of by-products. Different lipase preparations have been tested in each reaction. In the synthetic reaction, the effective removal of produced water was found to be vital for the production of triolein. With water removal and glycerol amounts not higher than required by the stoichiometry of the reaction, 95% of the available oleic acid was converted to triolein in 48 hr. The production of triolein was also found to be dependent on the availability of the 1,2-diglyceride to react with oleic acid. In the hydrolysis reaction, best conversion yields of triolein towards monoolein, diolein and free fatty acid were obtained when water was considered simply as a substrate of the reaction. In glycerolysis reactions, the reaction of triolein to give monoolein and diolein followed much the same pattern as for hydrolysis, when water was replaced by glycerol. It was shown again that near stoichiometric amounts of substrates led to the best conversion to mono- and diglycerides. A small excess of glycerol was found to be very inhibitory to the reaction. All possible isomers were formed during the reaction. Conversely, in alcoholysis reactions between triolein and stearyl alcohol the specificity of the lipase was upheld. Excess alcohol in this instance was found to be beneficial.     

Lipase-catalyzed synthesis of kojic acid esters in organic solvents

Kojic acid is an inhibitor of bacteria, viruses, and fungi. It is used for inhibiting the browning effect of tyrosinase in the food and cosmetic industries. To improve its lipophilic properties, Pseudomonas cepacia lipase and Penicillium camembertii lipase were used for catalyzing the esterification of kojic acid to synthesize kojic acid monolaurate and kojic acid monooleate. These products showed a 69.5% inhibitory effect on tyrosinase in hydrophobic organic solvent. The yields of kojic acid esters were affected by enzymes, substrates, organic solvent, and temperature. Lauric and oleic acids were the best substrates for esterification among various fatty acids tested. CaCl₂ and MnCl₂ stimulate Pseudomonas cepacia lipasecatalyzed esterification by 7.0%. On the contrary, MgCl₂, SrCl₂, and ZnCl₂ inhibited the reaction. The best pH of buffer for lipase pretreatment was pH 6.0. Pseudomonas and Penicillium lipases can be reused for the synthesis of kojic acid esters. After reaction at 40°C for 10 d, the Penicillium and Pseudomonas lipases still retained 57.0% and 92.0% of their initial activities, respectively.     

Pseudomonas fluorescens Lipase-catalysed Interesterification of Butter Fat

Butter fat was subjected to interesterification reactions catalysed by Pseudomonas fluorescens lipase in media of variable water content. The reaction products were analysed by gas chromatography on an immobilised phenylmethylsilicone capillary column. Triacylglycerol compositions were determined by normalisation, and free fatty acid and mono-and diacylglycerol compositions and contents by internal standardisation. In general, the triacylglycerol compositions of interesterification products were similar to each other and distinctly different from those of untreated butter fat. The compositions of triacylglycerols of the reaction products were similar to the composition calculated according to random distribution, except for the higher proportions of saturated triacylglycerols with 36 and 42–50 acyl carbons and monoene triacylglycerols with 38 acyl carbons in the reaction products. Enzymatic deacylation of reaction products showed the fatty acyl groups to be nearly randomly distributed among the three positions of glycerol. The contents of the hydrolysis products (MAGs, DAGs and FFAs) depended on the water content of the reaction medium.     

Kinetics of esterification of lauric acid with fatty alcohols by lipase: effect of fatty alcohol

Lauric acid has been esterified with some C₁–C₁₈ aliphatic alcohols by a commercial lipase, Lipolase 100 L, using isooctane as a solvent. When lauric acid and fatty alcohols were taken in the mole ratio 1:1, first order kinetics were observed for all the alcohols studied. The highest reaction rate was observed for n‐butyl alcohol. Lauric acid was esterified with stearyl alcohol, in varying acid to alcohol mole ratios to explain the first order kinetics of the reaction. A kinetic model for the lipase‐catalysed esterification in a biphasic organic–aqueous system has been proposed. Based on the interfacial substrate concentration, an analytical rate equation for initial rate of the reaction was derived and confirmed with the experimental data. © 2002 Society of Chemical Industry     

Feed batch addition of saccharide during saccharide-fatty acid esterification catalyzed by immobilized lipase: Time course,water activity,and kinetic model

A conversion of 80–93% was achieved for esterification of oleic acid and fructose (or sucrose) catalyzed by immobilized Rhizomucor miehei lipase (Lipozyme IM; Novozymes, Franklinton, NC) at 65°C using near-stoichiometric amounts of substrates. The product consisted of mono- and diester at a ratio of 9∶1 gg⁻¹. The main obstacle for achieving a high rate of reaction, the poor miscibility of the substrates, was overcome by taking advantage of the greatly increased solubility of fructose as the proportion of ester increased. A phase diagram demonstrated that the solubility of fructose increased linearly from 0.002 to 0.07 to 0.13 gg⁻¹ as the ester mass fraction increased from 0.00 to 0.47 to 0.80, respectively. Solvent (tert-butanol) was present only during the first phase of the time course of the reaction to enhance fructose solubility and was allowed to evaporate away completely on reaching 25% conversion. A conversion higher than 80–93% could not be achieved by reducing the bioreactor's water content through use of vacuum pressure or water activity control. Water adsorption isotherms demonstrate the significant increase of equilibrium liquid phase water content as the reaction progressed, which was due to higher water adsorption by the monoester relative to oleic acid. Increased removal of liquid phase water may result in the loss of water from the lipase, resulting in a reduction of its biocatalytic activity. Initial rate experiments were used to derive a Ping-Pong Bi Bi kinetic model that strongly agreed with measured data for the time course of the reaction. Lipozyme IM did not lose activity when employed for three successive fructose-oleate esterification batch reactions or, equivalently, for a 24-d reaction period.     

Enzymatic synthesis of l-menthyl esters in organic solvent-free system

l-Menthol has been widely used as a food additive and an ingredient of cosmetics, and it is esterified to moderate the strong flavor. We attempted esterification of l-menthol with long-chain unsaturated fatty acid in an organic solvent-free enzymatic system. Commercially available lipases were screened, and Candida rugosa lipase was selected as a catalyst. Several factors affecting the esterification were investigated, and the reaction conditions were determined as follows: A reaction mixture of l-menthol/fatty acid (1:3, mol/mol), 30% water, and 700 units of the lipase per gram of reaction mixture was incubated at 30°C with stirring. After 24 h under these conditions, the esterification extents of l-menthol with oleic, linoleic, and α-linolenic acids reached 96, 88, and 95%, respectively. The structure of the esterified product was confirmed by mass, infrared, and nuclear magnetic resonance spectroscopies. Bacause Candida lipase acted strongly on l-menthol and very weakly on d-menthol, dl-menthol was esterified with oleic acid under the same conditions. The reaction showed high enantioselectivity; the enantiomeric ratio (E) was 31, and enantiomeric excess (ee) of l-menthyl oleate reached 88% after 32 h.     

Strategies for the enzymatic enrichment of PUFA from fish oil

PUFA from oil extracted from Nile perch viscera were enriched by selective enzymatic esterification of the free fatty acids (FFA) or by hydrolysis of ethyl esters of the fatty acids from the oil (FA‐EE). Quantitative analysis was performed using RP‐HPLC coupled to an evaporative light scattering detector (RP‐HPLC‐ELSD). The lipase from Thermomyces lanuginosus discriminated against docosahexaenoic acid (DHA) most, resulting in the highest DHA/DHA‐EE enrichment while lipase from Pseudomonas cepacia discriminated against eicosapentaenoic acid (EPA) most, resulting in the highest EPA/EPA‐EE enrichment. The lipases discriminated between DHA and EPA with a higher selectivity when present as ethyl esters (EE) than when in FFA form. Thus when DHA/EPA were enriched to the same level during esterification and hydrolysis reactions, the DHA‐EE/EPA‐EE recoveries were higher than those of DHA/EPA‐FFA. In reactions catalysed by lipase from T. lanuginosus, at 26 mol% DHA/DHA‐EE, DHA recovery was 76% while that of DHA‐EE was 84%. In reactions catalysed by lipase from P. cepacia, at 11 mol% EPA/EPA‐EE, EPA recovery was 79% while that of EPA‐EE was 92%. Both esterification of FFA and hydrolysis of FA‐EE were more effective for enriching PUFA compared to hydrolysis of the natural oil and are thus attractive process alternatives for the production of products highly enriched in DHA and/or EPA. When there is only one fatty acid residue in each substrate molecule, the full fatty acid selectivity of the lipase can be expressed, which is not the case with triglycerides as substrates.     

Effect of pressure on the extractive biocatalysis of ethanol

The effect of pressure on the esterification reaction of ethanol with water-immiscible organic acids, catalysed by a lipase from Mucor miehei (pH 4.5; 30°C), was studied through analysis of the kinetics and equilibrium parameters. An increase of the ethanol distribution between the aqueous and organic phases was observed by the addition of lipase and the increase of the pressure in the system. Furthermore, the enzyme showed high specificity for the acid substrate, esterifying preferentially long chain fatty acids (C₈-C₁₈). In the studies described oleic acid was used as substrate for the esterification reaction. A kinetic study with the free enzyme, showed that pressure affected the extraction system, increasing the maximum reaction rate (> V_max), the affinity (< K_m) and the specificity (> V_max/K_m = k_sp) of the enzyme to the substrate, probably due to the effect of pressure on the electrostatic interactions in biological systems. The enzyme operational stability, at 30°C, improved significantly with the increase of pressure, having lower values for the deactivation constant (k) (8.3 × 10^?3 h^?1) and higher values for the half-life times (t_1/2) (77 h) in comparison with those obtained under atmospheric pressure conditions (k = 2.3 × 10^?2h^?1; t_1/2 = 30 h).