L. Gubicza

Enzymatic Biodiesel Production from Sunflower Oil by Candida antarctica Lipase in a Solvent-free System

Methanolysis (transesterification with methanol) of sunflower oil by lipase from Candida antarctica (Novozym 435) in a solvent-free system has been studied. Stepwise as well as continuous methanol feeding was applied to avoid strong substrate inhibition. Glycerol was found to cause strong product inhibition on the enzymatic reaction, therefore glycerol removal by dialysis was investigated using a flat sheet membrane module.

On the background of enhanced stability and reusability of enzymes in ionic liquids

The ability of ILs (ionic liquids) to provide an environment of increased stability and, in this way, improve the recyclability of enzymes has been studied. The description of this phenomenon is not easy; there are several approaches for explanation. In this mini-review, the results from different research groups are summarized, with the aim of explaining the strong stability effect of ILs on several enzymes. Spectroscopic methods (e.g. fluorescence and CD, IR spectroscopy, mass spectroscopy and NMR) and investigations of polarity and kosmotropicity of ions are promising methods. Since higher stability means that we may be able to reuse enzymes more times, the recyclability of enzymes was also in the focus. From this point of view, the advantages and disadvantages of applying monophasic or biphasic systems are discussed too, presenting the coupled techniques as well.

Large-scale enzymatic production of natural flavour esters in organic solvent with continuous water removal

A new, large-scale process was developed for the enzymatic production of low molecular weight flavour esters in organic solvent. Solutions for the elimination of substrate and product inhibitions are presented. The excess water produced during the process was continuously removed by hetero-azeotropic distillation and esters were produced at yields of over 90%.

Thermal stability enhancement of Candida rugosa lipase using ionic liquids

The thermal stability of Candida rugosa (C. rugosa) lipase was investigated and compared in n-hexane, benzene, dibutyl-ether as well as [bmim]PF6 and [omim]PF6 ionic liquids and the effect of solvent polarity and water activity were evaluated. Deactivation of the enzyme followed a series-type kinetic model. First order deactivation rate constants and the ratios of specific activities were determined and the kinetics of deactivation were studied. Among the organic solvents, the best stability was observed in n-hexane with a half-life of 6.5 h at water activity of 0.51. In ionic liquids, however, even longer half lives were obtained, and the enzyme was stable in these solvents at 50°C. The highest half-life times were obtained in [bmim]PF6 (12.3 h) and [omim]PF6 (10.6 h). A direct correlation was found between solvent polarity and thermal stability since the higher the polarity of the solvent, the lower was the stability decrease at 50°C comparing to that at 30°C.

Waste-free process for continuous flow enzymatic esterification using a double pervaporation system

The enzyme catalytic esterification reaction of acetic acid and ethanol in [bmim]PF6 ionic liquid was studied to manufacture natural ethyl acetate by a continuous waste-free process. The optimal parameters of the reaction were determined in batch experiments, and then a continuous set-up was constructed. Ethyl acetate and water formed in the bioreactor were removed by a double pervaporation system using hydrophobic and hydrophilic membranes, respectively. Acetic acid and ethanol were added as they were consumed, thus steady state concentrations in the reactor were maintained and continuous operation for 72 hours long was ensured without any activity loss of the enzyme.

A study on applications of membrane techniques in bioconversion of fumaric acid to L-malic acid

Abstract Membrane separation processes were applied in the fumaric acid—L-malic acid bioconversion. Electrodialysis was found suitable to recover the free malic acid from its salt (malate), formed in the reaction. Moreover the electrodialytic separation method can be on-line connected to the biochemical process forming an effective integrated system.

Enzymatic hydrolysis of polysaccharides: Hydrolysis of starch by an enzyme complex from fermentation by Aspergillus awamori

In this work an amylolitic enzyme complex—obtained from fermentation of whole wheat flour by Aspergillus awamori—was used for starch hydrolysis in batch and continuous (hollow fibre membrane bioreactor) systems. In the batch system a model was applied to describe glucose production. The continuous enzyme membrane system worked more efficiently compared to the batch system at low substrate concentrations.

Microwave assisted enzymatic esterification of lactic acid and ethanol in phosphonium type ionic liquids as co-solvents

Microwave heating was found to have a beneficial effect on the enzymatic esterification of lactic acid (LA) with ethanol in Cyphos 202 ionic liquid (IL) medium. Microwave irradiation caused hydrolysis of lactoyllactic acid (the linear dimer of LA) during the reaction, thus, as a result, more lactic acid was available as substrate and a higher ester yield was achieved in the esterification.

Unique role of water content in enzymatic synthesis of ethyl lactate using ionic liquid as solvent

Enzymatic synthesis of ethyl lactate was studied in organic solvents and in ionic liquids to determine optimal media for the reaction, and to investigate the effect of water content on the ester yield. Experiments proved that Cyphos 202 ionic liquid is the best solvent affording the highest ethyl lactate yields. Furthermore, 20 times less enzyme sufficed to carry out the reaction in this ionic liquid compared to organic solvents; ionic liquid could be applied as solvent. Using water removal, the ester yield decreased since a side reaction, dimerization of lactic acid, occurred as well. In contrast to these results, without water removal, the produced water was partly consumed by the decomposition of lactoyllactic acid to free lactic acid, increasing thus the substrate concentration of the mixture and enhancing the ester yield.

Coupled membrane process applied to fruit juice concentration

A coupled membrane process of membrane distillation and osmotic evaporation, where the solutions were thermostated separately at different temperatures, was developed. Enhanced water flux was obtained since the total driving force of the coupled process was higher than the sum of the driving forces of single processes. Apple, raspberry, sour cherry, red, and black currant juices were concentrated by the novel, mild technique.