Sonia Moreno-Perez

Synthesis of ascorbyl oleate by transesterification of olive oil with ascorbic acid in polar organic media catalyzed by immobilized lipases.

The reaction of transesterification between oils (e.g., olive oil) and ascorbic acid in polar anhydrous media (e.g., tert-amyl alcohol) catalyzed by immobilized lipases for the preparation of natural liposoluble antioxidants (e.g., ascorbyl oleate) was studied. Three commercial lipases were tested: Candida antarctica B lipase (CALB), Thermomyces lanuginosus lipase (TLL) and Rhizomucor miehei lipase (RML). Each lipase was immobilized by three different protocols: hydrophobic adsorption, anionic exchange and multipoint covalent attachment. The highest synthetic yields were obtained with CALB adsorbed on hydrophobic supports (e.g., the commercial derivative Novozym 435). The rates and yields of the synthesis of ascorbyl oleate were higher when using the solvent dried with molecular sieves, at high temperatures (e.g. 45°C) and with a small excess of oil (2 mol of oil per mol of ascorbic acid). The coating of CALB derivatives with polyethyleneimine (PEI) improved its catalytic behavior and allowed the achievement of yields of up to 80% of ascorbyl oleate in less than 24h. CALB adsorbed on a hydrophobic support and coated with PEI was 2-fold more stable than a non-coated derivative and one hundred-fold more stable than the best TLL derivative. The best CALB derivative exhibited a half-life of 3 days at 75°C in fully anhydrous media, and this derivative maintained full activity after 28 days at 45°C in dried tert-amyl alcohol.

Enzymatic synthesis of triacylglycerols of docosahexaenoic acid: Transesterification of its ethyl esters with glycerol.

The synthesis of docosahexaenoyl triacylglycerides at low temperature (e.g., 50°C) using biocatalysts of 6 commercial lipases adsorbed on hydrophobic supports was studied. In general, the triacylglyceride yields were very low with the exceptions of those produced with the enzymes from Candida antarctica fraction B, CALB (82%), and those produced with the enzyme from Pseudomonas fluorescens, PFL (57%). The reactions were performed under vacuum to remove the released ethanol. The yields varied widely when different derivatives of CALB were used, and they were higher when CALB adsorbed on hydrophobic supports was used (82%). One interesting by-product (18% of sn-2 monoacylglyceride of DHA) remained at the end of the synthetic process. CALB adsorbed on Sepabeads exhibited better activity and stability than did the commercial derivative Novozym 435. The best CALB biocatalyst preserved 90% of the activity after 30days under the reaction conditions.

Intense PEGylation of Enzyme Surfaces: Relevant Stabilizing Effects

This chapter describes the physicochemical coating of the surface of immobilized enzymes with a dense layer of polyethylene glycol (PEG) to improve enzyme stability. One hypothesis is that a dense, viscous, polar PEG layer around the enzyme would enhance enzyme thermal stability, while still providing access to the active site. PEG groups were attached by using aldehyde-dextran polymers, the dextran polymers are in turn attached to the enzyme surface that have been enriched with excess primary amino groups. The enzymes themselves were initially attached onto porous solids such that they may be separated easily from the reaction mixtures for easy downstream processing and that they may be recycled to reduce the cost of the biocatalyst. The hierarchical modification of enzyme surface with three different sublayers, under chemical design, provided a rational control at several structural levels. Few methods for increasing the number of amino groups on the surface of the enzyme are described: (a) chemical amination of carboxyl residues and (b) coating of the enzyme surface with cationic polymers containing a high percentage of primary amines. Reliable protocols for the PEGylation of four different enzymes are described here. For example, lipases from Thermomyces lanuginosa, Candida antarctica B, and Rhizomucor miehei attached to octyl sepharose and chemically modified via PEGylation are stabilized from 7- to 50-fold when compared to the stability of the corresponding unmodified enzyme. A derivative of endoxylanase from Trichoderma reesei, immobilized by multipoint covalent attachment on glyoxyl agarose, is stabilized by 50-fold. Very likely, the PEG layer generated a dense, high viscosity medium surrounding the enzyme surface and this increase in viscosity around the enzyme microenvironment resists distortion of enzyme structure by heat or other denaturing agents.

Immobilization of Lipase from Penicillium sp. Section Gracilenta (CBMAI 1583) on Different Hydrophobic Supports: Modulation of Functional Properties

Lipases are promising enzymes that catalyze the hydrolysis of triacylglycerol ester bonds at the oil/water interface. Apart from allowing biocatalyst reuse, immobilization can also affect enzyme structure consequently influencing its activity, selectivity, and stability. The lipase from Penicillium sp. section Gracilenta (CBMAI 1583) was successfully immobilized on supports bearing butyl, phenyl, octyl, octadecyl, and divinylbenzyl hydrophobic moieties wherein lipases were adsorbed through the highly hydrophobic opened active site. The highest activity in aqueous medium was observed for the enzyme adsorbed on octyl support, with a 150% hyperactivation regarding the soluble enzyme activity, and the highest adsorption strength was verified with the most hydrophobic support (octadecyl Sepabeads), requiring 5% Triton X-100 to desorb the enzyme from the support. Most of the derivatives presented improved properties such as higher stability to pH, temperature, and organic solvents than the covalently immobilized CNBr derivative (prepared under very mild experimental conditions and thus a reference mimicking free-enzyme behavior). A 30.8- and 46.3-fold thermostabilization was achieved in aqueous medium, respectively, by the octyl Sepharose and Toyopearl butyl derivatives at 60 °C, in relation to the CNBr derivative. The octyl- and phenyl-agarose derivatives retained 50% activity after four and seven cycles of p-nitrophenyl palmitate hydrolysis, respectively. Different derivatives exhibited different properties regarding their properties for fish oil hydrolysis in aqueous medium and ethanolysis in anhydrous medium. The most active derivative in ethanolysis of fish oil was the enzyme adsorbed on a surface covered by divinylbenzyl moieties and it was 50-fold more active than the enzyme adsorbed on octadecyl support. Despite having identical mechanisms of immobilization, different hydrophobic supports seem to promote different shapes of the adsorbed open active site of the lipase and hence different functional properties.

Immobilization and stabilization of commercial β-1,4-endoxylanase Depol™ 333MDP by multipoint covalent attachment for xylan hydrolysis: Production of prebiotics (xylo-oligosaccharides)

Abstract The commercial enzyme Depol™ 333MDP (D333MDP) was immobilized by multipoint covalent attachment onto 10% cross-linked agarose beads support highly activated with aldehyde groups. The enzyme immobilization process was very efficient, retaining 86% of its initial catalytic activity. Thermal stability of the immobilized D333MDP biocatalysts varied according to the incubation time of the enzyme-support. The optimal immobilized biocatalyst was produced after 24 h of incubation under alkaline conditions and longer incubation times resulted in a loss of stability. The optimal immobilized biocatalyst was 60- and 50-fold more stable at pH 5.5 and pH 7 at 50 °C than the soluble enzyme, respectively. Activity and stability at pH 5.5 were enhanced when the optimal immobilized biocatalyst was modified by chemical amination of the enzyme surface. The chemical amination of the immobilized enzyme surface was 5-fold more stable at pH 5.5 and 50 °C compared with the unmodified immobilized biocatalyst. The best immobilized biocatalysts (containing 100 UI/g of support) were evaluated in the beechwood xylan hydrolysis reaction at 50 °C and pH 5.5. 80% of the reducing sugars were released after 6 h of hydrolysis with the aminated biocatalyst. Xylan hydrolysis reaction with the aminated biocatalyst was 80% faster than with the non-aminated one. The final composition of the xylooligosaccharides (XOS) obtained was identified and quantified by HPAEC-PAD which showed it was composed of 90% of xylobiose and 5% of xylotriose and xylose. The aminated immobilized-stabilized biocatalyst was used for four cycles of hydrolysis with no loss of catalytic activity, resulting in highly active and stable derivative suitable for industrial processes.

Preparation of a robust immobilized biocatalyst of β-1,4-endoxylanase by surface coating with polymers for production of xylooligosaccharides from different xylan sources

Xylooligosaccharides display interesting prebiotic effects on human health. The endoxylanase Xys1Δ, from Streptomyces halstedii JM8, was immobilized and stabilized on glyoxyl-agarose beads by multipoint covalent attachment using a novel strategy based on surface coating with a multilayer of polymers. The optimal modification consisted of surface coating with a bilayer formed by a layer of derived dextran polymers and a layer of polyethylenimine. The optimized biocatalyst was 550-fold more stable than one-point covalent immobilized Xys1Δ (at 70 °C, pH 7). This biocatalyst was tested for the production of xylooligosaccharides from soluble xylans from various sources. Hydrolysis of beechwood, wheat straw and corncob xylans was 93% in 4 h, 44% in 5 h and 100% in 1 h, respectively. Maximum values of xylooligosaccharides were found for beechwood at 20.6 mg/mL, wheat at 12.5 mg/mL and corncob at 30.4 mg/mL. The optimized biocatalyst was reused for 15 reaction cycles without affecting its catalytic activity.

Critical Role of Different Immobilized Biocatalysts of a Given Lipase in the Selective Ethanolysis of Sardine Oil

Different immobilized derivatives of two lipases were tested as catalysts of the synthesis of ethyl esters of omega-3 fatty acids during the ethanolysis of sardine oil in solvent-free systems at 25 °C. Lipases from Thermomyces lanuginosus (TLL) and Lecitase Ultra (a phospholipase with lipolytic activity) were studied. Lipases were adsorbed on hydrophobic Sepabeads C18 through the open active center and on an anion-exchanger Duolite with the active center exposed to the reaction medium. TLL-Sepabeads derivatives exhibit a high activity of 9 UI/mg of immobilized enzyme, and they are 20-fold more active than TLL-Duolite derivatives and almost 1000-fold more active than Lipozyme TL IM (the commercial derivative from Novozymes). Lecitase-Sepabeads exhibit a high selectivity for the synthesis of the ethyl ester of EPA that is 43-fold faster than the synthesis of the ethyl ester of DHA.

Stabilization of Immobilized Lipases by Intense Intramolecular Cross-Linking of Their Surfaces by Using Aldehyde-Dextran Polymers

Immobilized enzymes have a very large region that is not in contact with the support surface and this region could be the target of new stabilization strategies. The chemical amination of these regions plus further cross-linking with aldehyde-dextran polymers is proposed here as a strategy to increase the stability of immobilized enzymes. Aldehyde-dextran is not able to react with single amino groups but it reacts very rapidly with polyaminated surfaces. Three lipases—from Thermomyces lanuginosus (TLL), Rhizomucor miehiei (RML), and Candida antarctica B (CALB)—were immobilized using interfacial adsorption on the hydrophobic octyl-Sepharose support, chemically aminated, and cross-linked. Catalytic activities remained higher than 70% with regard to unmodified conjugates. The increase in the amination degree of the lipases together with the increase in the density of aldehyde groups in the dextran-aldehyde polymer promoted a higher number of cross-links. The sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis of those conjugates demonstrates the major role of the intramolecular cross-linking on the stabilization of the enzymes. The highest stabilization was achieved by the modified RML immobilized on octyl-Sepharose, which was 250-fold more stable than the unmodified conjugate. The TLL and the CALB were 40-fold and 4-fold more stable than the unmodified conjugate.

Designing continuous flow reaction of xylan hydrolysis for xylooligosaccharides production in packed-bed reactors using xylanase immobilized on methacrylic polymer-based supports

The present study focuses on the development and optimization of a packed-bed reactor (PBR) for continuous production of xylooligosaccharides (XOS) from xylan. For this purpose, three different methacrylic polymer-based supports (Relizyme R403/S, Purolite P8204F and Purolite P8215F) activated with glyoxyl groups were morphologically characterized and screened for the multipoint covalent immobilization of a xylanase. Based on its physical and mechanical properties, maximum protein loading and thermal stability, Relizyme R403/S was selected to set up a PRB for continuous production of XOS from corncob xylan. The specific productivity for XOS at 10 mL/min flow rate was 3277 gXOS genzyme-1 h-1 with a PBR. This PBR conserved >90% of its initial activity after 120 h of continuous operation.

Enzymatic transesterification in a solvent-free system: synthesis of sn-2 docosahexaenoyl monoacylglycerol

Abstract The enzymatic transesterification of docosahexaenoic acid (DHA) ethyl ester with glycerol was carried out by using several immobilized lipases in a solvent-free system. This reaction involves the initial formation of sn-2 docosahexaenyl monoacylglycerol. This DHA derivative is highly relevant for improving the bioavailability of DHA and it has received increasing interest in the field of nutrition. Three commercial lipases, from Rhizomucor miehei (RML), Alcaligenes sp. (AQ) and Candida antarctica-fraction B (CALB) were immobilized by interfacial adsorption on a commercial hydrophobic support (a methacrylate resin containing octadecyl groups, Sepabeads C-18) and tested for glycerolysis of DHA ethyl ester. In certain cases (e.g. immobilized CALB), the transesterification reaction continues to the formation of triacylglycerol (80%) by using a very high excess of DHA ethyl ester ((115 mmols versus 1.24 mmols of glycerol and high temperatures (50 °C). However, the same biocatalyst working at lower temperatures, 37 °C, synthetizes a 90% of sn-2 monoacylglycerol even in the presence of that a high excess of DHA ethyl ester. Interestingly, immobilized RML derivative synthesizes a 98% of sn-2 monoacylglyceride (2-MG) in 15 min at 37 °C with a 4% of immobilized biocatalyst. These high activity and regioselectivity under very mild reaction conditions are very interesting for the thermal oxidative stability of the omega-3 fatty acid as well as for the thermal stability of the biocatalyst. Using Normal Phase HPLC-ELSD and accurate commercial markers, the formation of the 2-MG was confirmed.