Modulation of the Selectivity of Immobilized Lipases by Chemical and Physical Modifications: Release of Omega-3 Fatty Acids from Fish Oil

Three different lipases (from Candida antarctica fraction B (CALB), Thermomyces lanuginose (TLL), and Rhizomucor miehei (RML)) were immobilized by two different methods, immobilization on CNBr-activated Sepharose via a mild covalent immobilization or adsorption onto hydrophobic supports (Octyl-Sepharose). These immobilized preparations were chemically and physically modified on the protein surface (enzyme carboxylic groups with ethylenediamine, amino groups with succinic anhydride, or coating with polyethyleneimine).The activity and selectivity in the production of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) by enzymatic hydrolysis of sardine oil were evaluated. Activity and selectivity were dependent on the different lipases, the immobilization protocols, the modification methods, and the pH of the reaction media. The selectivity (EPA/DHA ratio) of RML immobilized on CNBr-activated Sepharose was increased after succinylation from 7.5 to 34 at pH 6.0. The selectivity of octyl-RML improved from 1.5 to 8.5 when pH was increased from 6 to 8. The selectivity and activity of octyl-TLL increased twofold after PEI coating at pH 6. The properties of CAL-B derivatives were slightly altered after modification.     

Selective Ethanolysis of Fish Oil Catalyzed by Immobilized Lipases

Selective ethanolysis of fish oil was catalyzed by immobilized lipases and their derivatives in organic media. Lipases from Candida antarctica B (CALB), Thermomyces lanuginosa (TLL) and Rhizomucor miehei (RML) were studied. The three lipases were immobilized by anion exchange and hydrophobic adsorption. The discrimination between the ethyl ester of eicosapentaenoic acid (EE-EPA) and the ethyl ester of docosahexaenoic acid (EE-DHA) depends on the lipase, the immobilization support, the physico-chemical modifications of the immobilized lipase derivatives and on the solvents used. TLL and RML were much more selective than CALB. EE-EPA is released 20-fold faster than EE-DHA when ethanolysis was catalyzed, in cyclohexane, by TLL hydrophobically adsorbed on Sepabeads C18. The selectivity and stability of the different derivatives in these polar organic solvents were further improved after physico-chemical modification. The best results for activity-selectivity-stability were obtained in cyclohexane for TLL adsorbed on Sepabeads C18 and further modified via solid-phase physical modification with a polyethylenimine polymer. In this case, the initial selectivity was higher than 20, and a 80 % of EPA was released as ethyl ester after 3 h at 25 °C. At this conversion, mixtures of ethyl esters highly enriched in the ethyl ester of EPA with less than 5 % of the EE-DHA were obtained. TLL derivatives remained fully active after incubation for 24 h in anhydrous solvents.     

Hydrolysis of Fish Oil by Lipases Immobilized Inside Porous Supports

A new assay was designed to measure the release of omega-3 acids [eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)] from the hydrolysis of sardine oil by lipases immobilized inside porous supports. A biphasic system was used containing the fish oil dissolved in the organic phase and the immobilized lipase suspended in the aqueous phase. The assay was optimized by using a very active derivative of Rhizomucor miehei lipase (RML) adsorbed onto octyl-Sepharose. Standard reaction conditions were: (a) an organic phase composed by 30/70 (v:v) of oil in cyclohexane, (b) an aqueous phase containing 50 mM methyl-cyclodextrin in 10 mM Tris buffer at pH 7.0. The whole reaction system was incubated at 25 °C. Under these conditions, up to 2% of the oil is partitioned into the aqueous phase and most of the 95% of released acids were partitioned into the organic phase. The organic phase was analyzed by RP-HPLC (UV detection at 215 nm) and even very low concentrations (e.g., 0.05 mM) of released omega-3 fatty acid could be detected with a precision higher than 99%. Three different lipases adsorbed on octyl-Sepharose were compared: Candida antarctica lipase-fraction B (CALB), Thermomyces lanuginosa lipase (TLL) and RML. The three enzyme derivatives were very active. However, most active and selective towards polyunsaturated fatty acids (PUFA) versus oleic plus palmitic acids (a fourfold factor) was CALB. On the other hand, the most selective derivatives towards EPA versus DHA (a 4.5-fold factor) were TLL and RML derivatives.     

Separation of EPA and DHA in fish oil by lipase-catalyzed esterification with glycerol

The objective of this study was to investigate the use of lipases as catalysts for separating EPA and DHA in fish oil by kinetic resolution based on their FA selectivity. Esterification of FFA from various types of fish oils with glycerol by immobilized Rhizomucor miehei lipase under water-deficient, solvent-free conditions resulted in a highly efficient separation of EPA and DHA. Reactions were conducted at 40°C with a 10% dosage of the lipase preparation under vacuum to remove the coproduced water, thus rapidly shifting the reaction toward the products. The bulk of the FA, together with EPA, were converted into acylglycerols, whereas DHA remained in the residual FFA. As an example, when FFA from tuna oil comprising 5% EPA and 25% DHA were esterified with glycerol, 90% conversion into acylglycerols was obtained after 48 h. The residual FFA contained 78% DHA and only 3% EPA, in 79% DHA recovery. EPA recovery in the acylglycerol fraction was 91%. The type of fish oil and extent of conversion were highly important parameters in controlling the degree of concentration.     

The preparation of concentrates of eicosapentaenoic acid and docosahexaenoic acid by lipase-catalyzed transesterification of fish oil with ethanol

The objective of this study was to investigate the use of lipases as catalysts for producing concentrates of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from fish oil as an alternative to conventional chemical procedures. Transesterification of fish oil with ethanol was conducted under anhydrous solvent-free conditions with a stoichiometric amount of ethanol. Among the 17 lipases tested, the results showed that Pseudomonas lipases had the highest activity toward the saturated and monounsaturated fatty acids in the fish oil, much lower activity toward EPA and DHA and, at the same time, good tolerance toward the anhydrous alcoholic conditions. With 10 wt% of lipase, based on weight of the fish oil triacylglycerol substrate (15% EPA and 9% DHA initial content), a 50% conversion into ethyl esters was obtained in 24 h at 20°C, in which time the bulk of the saturated and monounsaturated fatty acids reacted, leaving the long-chain n-3 polyunsaturated fatty acids unreacted in the residual mixture as mono-, di-, and triacylglycerols. This mixture comprised approximately 50% EPA+DHA. Total recovery of DHA and EPA was high, over 80% for DHA and more than 90% for EPA. The observed fatty acid selectivity, favoring DHA as a substrate, was most unusual because most lipases favor EPA.     

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.     

Lipase-catalyzed incorporation of n−3 PUFA into palm oil

Two immobilized lipases, IM60 from Rhizomucor miehei and QLM from Alcaligenes sp., were used as biocatalysts for the modification of the FA composition of palm oil by incorporating n−3 PUFA. Acidolysis and interesterification reactions were conducted with hexane as organic solvent, and the products were analyzed by using GLC. After a 24-h incubation in hexane, there was an average incorporation of 20.8% EPA and 15.6% DHA into palm oil, respectively, while the percentages of palmitic and oleic acids in palm oil decreased by 28.8 and 11.8%, respectively. Higher EPA and DHA incorporation was obtained when EPAX (fish oil concentrate high in n−3 PUFA) was used in the ethyl ester form (interesterification reaction) than in the free acid form (acidolysis) in the presence of Lipozyme (IM60 lipase. Lipase QLM was found to discriminate against EPA, and it showed slightly better catalytic activity for DHA in the free acid form than in the ethyl ester form. Generally, as the mole ratio of the acyl donor to TAG increased, the percentage incorporation of EPA and DHA increased; however, reactions catalyzed by Lipozyme IM60 did not show increases in the incorporation beyond a TAG/EPAX mole ratio of 3. When limitations due to mass transfer were not a factor, an increase in the reactant amount also gave an increase in the percentage incorporation of the n−3 PUFA. Palm oil containing EPA and DHA was successfully produced and may be beneficial in certain food and nutritional applications.     

Lipase‐catalysed enrichment of DHA and EPA in acylglycerols resulting from squid oil ethanolysis

The fatty acid specificity of four lipases towards eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) was evaluated when performing ethanolysis of squid oil. During the first part of ethanolysis, no DHA ethyl esters were detected when using the lipases from Thermomyces lanuginosus, Pseudomonas cepacia or Pseudomonas fluorescens (in the case of the second and third lipases, no EPA ethyl esters were detected either). This indicates that these three lipases could not catalyse the conversion of DHA located in a triacylglycerol to ethyl ester, and that the Pseudomonas lipases could not catalyse the conversion of EPA either. This pattern was not found for the lipase from Rhizomucor miehei. The lipase from Thermomyces lanuginosus showed the lowest specificity towards DHA and the highest DHA recovery during DHA enrichment in the acylglycerol fraction. It was thus used to catalyse the ethanolysis of squid oil on a larger scale. The ethyl esters formed were removed using short‐path distillation, resulting in a product containing mainly mono‐ and diacylglycerols. The product contained 34 mol‐% DHA and 17 mol‐% EPA, compared with 19 mol‐% DHA and 12 mol‐% EPA in the original squid oil.     

Enzymic synthesis of fatty esters by hydrophobic lipase derivatives immobilized on organic polymer beads

Lipase fromCandida rugosa was modified with several hydrophobic modifiers before being adsorbed onto organic polymer beads. The effects of different enzyme modifiers, supports, solvents, reaction temperatures, fatty acids, and alcohols on the activity of the immobilized enzyme were investigated. The immobilized lipases were good biocatalysts for esterification reactions in organic solvents. They exhibited high activities in all solvents tested, including polar solvents. The activity seemed to depend on the type of support rather than on the modifier of the enzyme. The medium polar support, XAD7, appeared to be the best for the modified lipases. The immobilized lipase favored the medium-chain fatty acids rather than the long-chain fatty acids as acyl donors. The alcohol selectivity of the enzyme was unchanged upon immobilization. The native and immobilized lipases favored the short-chain and terpene alcohols as nucleophiles.     

Separation of eicosapentaenoic acid and docosahexaenoic acid in fish oil by kinetic resolution using lipase

The objective of this study was to investigate the use of lipases as catalysts for separating eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in fish oil by kinetic resolution. Transesterification of various fish oil triglycerides with a stoichiometric amount of ethanol by immobilized Rhizomucor miehei lipase under anhydrous solvent-free conditions resulted in a good separation. When free fatty acids from the various fish oils were directly esterified with ethanol under similar conditions, greatly improved results were obtained. By this modification, complications related to regioselectivity of the lipase and nonhomogeneous distribution of EPA and DHA into the various positions of the triglycerides were avoided. As an example, when tuna oil comprising 6% EPA and 23% DHA was transesterified with ethanol, 65% conversion into ethyl esters was obtained after 24 h. The residual glyceride mixture contained 49% DHA and 6% EPA (8:1), with 90% DHA recovery into the glyceride mixture and 60% EPA recovery into the ethyl ester product. When the corresponding tuna oil free fatty acids were directly esterified with ethanol, 68% conversion was obtained after only 8h. The residual free fatty acids comprised 74% DHA and only 3% EPA (25:1). The recovery of both DHA into the residual free fatty acid fraction and EPA into the ethyl ester product remained very high, 83 and 87%, respectively.     

Lipase-catalyzed enrichment of long-chain polyunsaturated fatty acids

Lipase hydrolysis was evaluated as a means of selectively enriching long-chain ω3 fatty acids in fish oil. Several lipases were screened for their ability to enrich total ω-3 acids or selectively enrich either docosahexaenoic acid (DHA) or eicosapentaenoic acid (EPA). The effect of enzyme concentration, degree of hydrolysis, and fatty acid composition of the feed oil was studied. Because the materials that were enriched in long-chain ω3 acids were either partial glycerides or free fatty acids, enzymatic reesterification of these materials to triglycerides by lipase catalysis was also investigated. Hydrolysis of fish oil by eitherCandida rugosa orGeotrichum candidum lipases resulted in an increase in the content of total ω3 acids from about 30% in the feed oil to 45% in the partial glycerides. The lipase fromC. rugosa was effective in selectively enriching either DHA or EPA, resulting in a change of either the DHA/EPA ratio or the EPA/DHA ratio from approximately 1:1 to 5:1. Nonselective reesterification of free fatty acids or partial glycerides that contained ω3 fatty acids could be achieved at high efficiency (approximately 95% triglycerides in the product) by using immobilizedRhizomucor miehei lipase with continuous removal of water.     

Concentration of docosahexaenoic acid in glyceride by hydrolysis of fish oil withcandida cylindracea lipase

In an attempt to concentrate the content of DHA (docosahexaenoic acid) in a glyceride mixture containing triglyceride, diglyceride and monoglyceride, fish oil was hydrolyzed with six kinds of microbial lipase. After the hydrolysis, free fatty acid was removed and fatty acid components of the glyceride mixtures were analyzed. When the hydrolysis withCandida cylindracea lipase was 70% complete, the DHA content in the glyceride mixture was three times more than that in the original fish oil. The EPA (eicosapentaenoic acid) content became almost 70% of the original fish oil. Hydrolysis with other lipases did not result in an increase in the DHA content in the glyceride mixtures. Hydrolysis of DHA-rich tuna oil (DHA content is about 25%) withCandida cylindracea lipase resulted in 53% DHA in the glyceride mixture. The EPA content, however, remained close to that of the original tuna oil. In this report, the acyl chain specificity of lipases is evaluated in terms of hydrolysis resistant value (HRV). HRV is the ratio between the DHA contents in the glyceride mixture of hydrolyzed oil and original oil. HRV clearly indicates differences in hydrolysis between DHA and other fatty acids (e.g., saturated and monoenoic acids).     

Lipase-assisted concentration of n-3 polyunsaturated fatty acids in acylglycerols from marine oils

Preparation of n-3 polyunsaturated fatty acid (PUFA) concentrates from seal blubber oil (SBO) and menhaden oil (MHO) in the form of acylglycerols was carried out by hydrolysis with a number of commercial microbial lipases. The lipases tested were Aspergillus niger, Candida cylindracea (CC), Chromobacterium viscosum, Geotrichum candidum, Mucor miehei, Pseudomonas sp., Rhizopus oryzae, and Rhizopus niveus. After lipase-assisted hydrolysis of oils, free fatty acids were removed, and fatty acid composition of the mixture containing mono-, di-, and triacylglycerols was determined. All lipases were effective in increasing the n-3 PUFA content of the remaining acylglycerols of both SBO and MHO. The highest concentration of n-3 PUFA was provided by CC lipase; 43.5% in SBO [9.75% eicosapentaenoic acid (EPA), 8.61% docosapentaenoic acid (DPA), and 24.0% docosahexaenoic acid (DHA)] and 44.1% in MHO (18.5% EPA, 3.62% DPA, and 17.3% DHA) after 40 h of hydrolysis. Thus, CC lipase appears to be most suitable for preparation of n-3 PUFA in the acylglycerol form from marine oils.     

Enrichment of polyunsaturated fatty acids withGeotrichum candidum lipase

Three lipases, isolated previously in our laboratory, each with different fatty acid and positional specificities, and a known lipase fromCandida cylindracea were screened for concentrating docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids in glycerides.Geotrichum candidum lipase was found to be suitable for their concentration in glycerides. Tuna oil was treated at 30°C with this lipase for 16 h, and 33.5% hydrolysis resulted in the production of glycerides containing 48.7% of DHA and EPA. The hydrolysis was not increased despite adding further lipase, so the glycerides were extracted, and the reaction was repeated. The second hydrolysis produced glycerides containing 57.5% of DHA and EPA in a 54.5% yield, with recovery of 81.5% of initial DHA and EPA. Of the total glycerides, 85.5% were triglycerides. These results showed thatG. candidum lipase was effective in producing glycerides that contained a high concentration of polyunsaturated fatty acids in good yield.     

固定化脂肪酶选择性富集鱼油ω-3多不饱和脂肪酸甘油酯

采用吸附与交联相结合的方法固定化米曲霉脂肪酶.脂肪酶固定化的参数条件：载体为硅藻土、吸附温度为25℃、吸附时间为6 h、pH值为7.0 KH₂PO₄-NaOH缓冲液、缓冲液离子强度为0.03 mol•L^-1、给酶量为900 U•（g硅藻土）^-1、交联剂为0.5％戊二醛、交联的时间为1.5 h,所得固定化酶酶活力为247 U•（g载体）^-1,蛋白载量为25 mg•（g硅藻土）^-1,水解鱼油操作半衰期为264 h.固定化脂肪酶富集鱼油中ω-3多不饱和脂肪酸甘油酯的最适条件是：温度38 ℃、油水比为1∶1、加酶量为150U•（g油）^-1、反应转速为200 r•min^-1、最佳富集时间为24 h.在此工艺条件下鱼油中EPA由3.0%提高到7.0%,DHA由4.3%提高到14.5%,EPA+DHA由7.3%提高到21.5%.     

Synthesis of structured triglycerides from peanut oil with immobilized lipase

Structured triglycerides (ST) that contain medium- and long-chain fatty acids were synthesized by lipase-catalyzed interesterification between tricaprylin and peanut oil. To select appropriate enzymes, we investigated nine commercial lipase preparations for their ability to hydrolyze pure triglycerides as well as natural oils. Three microbial lipases from Rhizomucor miehei (RML), Candida sp. (CSL), and Chromobacterium viscosum (CVL) gave good results, and immobilized preparations were used in the interesterification. RML gave the highest yields of ST (73%, 40°C), although its hydrolytic activity toward triolein was low. As the temperature was raised to 50°C, the yield of ST increased to 79%. After 120 h reaction time, remaining activities were high for CSL (71%), moderate for CVL (48%), and low for RML (20%). Parts of this paper were presented as a poster at the Biochemical Engineering Conference IX, May 1995, Davos, Switzerland.     

Release of Omega-3 Fatty Acids by the Hydrolysis of Fish Oil Catalyzed by Lipases Immobilized on Hydrophobic Supports

The release of omega-3 fatty acids by the mild enzymatic hydrolysis of sardine oil was studied. The derivatives of different lipases physically adsorbed on hydrophobic porous supports Hydrophobic Lipase Derivatives (HLD) were tested. These immobilized lipases can only hydrolyze oil molecules partitioned into the aqueous phase of a biphasic reaction system. HLD biocatalysts were compared to other enzyme derivatives that were obtained by very mild covalent immobilization on CNBr-activated Sepharose Cyanogen bromide Lipase Derivatives (CNLD) that behave almost identically to soluble enzymes (CNLD). In general, HLD biocatalysts were found to be more active and more selective for the release of eicosapentaenoic acid (EPA) than CNLD. The most interesting biocatalyst was the HLD derivative of Yarrowia lipolytica lipase, which was found to be sevenfold more active and tenfold more selective than CNLD. On the other hand, the most active (but non-selective) derivative was the HLD of Pseudomonas fluorescens lipase (PFL). The activity of this derivative was 0.6 International Units under non-optimal reaction conditions. High-loaded PFL derivatives could be very interesting for the release of mixtures of EPA and docosahexaenoic acid. Hydrophobic supports promote the interfacial activation of lipases, similar to the interaction promoted by oil drops on soluble enzymes. The most effective overactivation obtained in this work ranged from 6- to 20-fold. The hydrolytic process was carried out under very mild conditions (pH 7.0 and 25 °C), and all lipase derivatives remained fully active for at least 15 days under these conditions.     

Functional display of Rhizomucor miehei lipase on surface of Saccharomyces cerevisiae with higher activity and its practical properties

BACKGROUND: A display system, which can translate DNA to functional peptides or proteins, is used as a new protein expression system. In this system, peptides or proteins are displayed on the cell surface as a fusion form with some anchoring proteins. Yeast cells displaying lipases on their cell‐surface could be used as whole‐cell biocatalysts. This research focuses on the functional display of Rhizomucor miehei lipase (RML) on the surface of Saccharomyces cerevisiae with higher activity. RESULTS: The lipases (RML) from R.miehei 3.4960 were of active form. The RML‐α‐agglutinin fusion proteins produced were not secreted into the culture media and were mostly immobilized on the yeast cells. Cell surface displayed lipase showed the highest activity at 45 °C and pH 8.0. CONCLUSION: The gene encoding RML from R.miehei 3.4960 can be functionally expressed on the cell surface of S. cerevisiae MT8‐1 using a glycosylphosphatidylinositol (GPI) anchor with higher activity. Copyright © 2007 Society of Chemical Industry     

Concentration of eicosapentaenoic acid by selective esterification using lipases

The aim of this work was to increase the content of EPA in FFA extracts from a commercial oil (43.1% EPA) and from Phaeodactylum tricornutum oil, a single-cell oil, by selective enzymatic esterification. Initially, the FFA extract was esterified with lauryl alcohol using nine lipases. All the lipases concentrated EPA in the unesterified FFA fraction. The criterion used to choose the best lipase was maximization of the dimensionless effectiveness factor (F_AE). This factor grouped the concentration factor (ratio between the EPA concentrations in the FFA fractions before and after esterification) with EPA recovery in the final FFA fraction. Experiments were carried out to correlate F_AE and the degree of esterification (ED, percentage of initial FA converted to lauryl esters). Lipase AK from Pseudomonas fluorescens was the most effective for concentrating EPA. Studies, of the optimal temperature, substrate molar ratio, solvent/substrate ratio, and treatment intensity (product of the lipase mass and the reaction time) were also carried out using the lipase. The maximum F_AE was obtained when the ED was 60%: EPA concentration was 72%, and recovery was 73%. Finally, this lipase was used to concentrate EPA from a FFA extract from P. tricornutum (23% EPA). The content of EPA in the unesterified FFA fraction increased to 71% at 78% ED (recovery of EPA, 75.5%). Comparison of the results of obtained with the two FFA extracts seemed to indicate that the selectivity of Lipase AK for EPA depended on the content of EPA, with higher contents of EPA in the initial FFA mixture reducing the selectivity for EPA.     

Immobilization of hydrophobic lipase derivatives on to organic polymer beads

A simple and effective method of lipase immobilization is described. Lipase from Candida rugosa was first modified with several hydrophobic modifiers before being adsorbed on to organic polymer beads. The soluble hydrophobic lipase derivatives adsorbed more strongly on to the various polymers as compared with the native lipase. The optimal adsorption temperature of the native and modified lipases on all the polymers was 40°C. The optimal pH of adsorption was between 6 and 7. Lipase immobilized in this manner produced high catalytic recoveries which were affected by the type of modifiers, degree of modification and type of supports used. Monomethoxypolyethylene glycol (1900) activated with p-nitrophenyl chloroformate was found to be the best modifier of the enzyme at 95% modification, for adsorption to the polymers. Increasing the degree of modification of the enzyme increased the activity which was immobilized. Generally, both native and hydrophobic lipase derivatives showed higher specific activities when immobilized on polar polymers compared with non-polar polymers.