Esterification of polyglycerol with polycondensed ricinoleic acid catalysed by immobilised Rhizopus oryzae lipase.

The enzymatic method for synthesising polyglycerol polyricinoleate (PGPR), a food additive named E-476, was successfully carried out in the presence of immobilised Rhizopus oryzae lipase in a solvent-free medium. The great advantage of using the commercial preparation of R. oryzae lipase is that it is ten times cheaper than the commercial preparation of R. arrhizus lipase, the biocatalyst used in previous studies. The reaction, which is really a reversal of hydrolysis, takes place in the presence of a very limited amount of aqueous phase. Immobilisation of the lipase by physical adsorption onto an anion exchange resin provided good results in terms of activity, enzyme stability and reuse of the immobilised derivative. It has been established that the adsorption of R. oryzae lipase on Lewatit MonoPlus MP 64 follows a pseudo-second order kinetics, which means that immobilisation is a process of chemisorption, while the equilibrium adsorption follows a Langmuir isotherm. The use of this immobilised derivative as catalyst for obtaining PGPR under a controlled atmosphere in a vacuum reactor, with a dry nitrogen flow intake, allowed the synthesis of a product with an acid value lower than 6 mg KOH/g, which complies with the value established by the European Commission Directive. This product also fulfils the European specifications regarding the hydroxyl value and refractive index given for this food additive, one of whose benefits, as proved in our experiments, is that it causes a drastic decrease in the viscosity (by 50 %) and yield stress (by 82 %) of chocolate, comparable to the impact of customary synthesised PGPR.

Screening of three commercial plant peroxidases for the removal of phenolic compounds in membrane bioreactors.

A comparative study of three plant peroxidases, horseradish (HRP), soybean (SBP) and artichoke (AKPC), was carried out to select the most appropriate one for 4-chlorophenol treatment in an ultrafiltration membrane reactor. Soybean peroxidase showed the highest enzymatic activity, followed by HRP and AKPC. The same tendency was observed in a discontinuous tank reactor, where SBP attained more than 90% of4-chlorophenol removal within the pH range tested. The optimum temperature was 30 degrees C, with SBP showing highest thermostability. With the ultrafiltration membrane reactor, SBP attained the highest operational stability, with 4-chlorophenol conversions of around 90% in the permeate stream for up to 200 minutes. Finally, permeate samples were analysed and no significant amount of enzyme was detected, so the observed loss of activity, less pronounced with SBP, was attributed to enzyme adsorption on the polymeric products deposited on the membrane surface. Soybean peroxidase was selected as the most appropriate peroxidase for future research.

Continuous tank reactors in series: an improved alternative in the removal of phenolic compounds with immobilized peroxidase.

Immobilized derivatives of soybean peroxidase, covalently bound to a glass support, were used in a continuous stirred tank reactor in series, in order to study the removal of two phenolic compounds: phenol and 4-chlorophenol. The use of two reactors in series, rather than one continuous tank, improved the removal efficiencies of phenol and 4-chlorophenol. The distribution of different amounts of enzyme between the two tanks showed that the relative distributions influenced the removal efficiency reached and the degree of the enzyme deactivation. The highest removal percentages were reached at the outlet of the second tank for a distribution of 50% of the enzyme in each tank. However, with a distribution of 75% in the first tank and 25% in the second, the elimination percentage in the second tank was slightly lower than in the previous case, and the effects of deactivation of the enzyme in the first tank were less pronounced. In all the distributions assayed it was observed that the first tank acts as a filter for the second one, which receives a feed with a smaller load of phenolic compounds, thus diminishing enzyme deactivation in the second tank.

Comparison of commercial peroxidases for removing phenol from water solutions.

This paper describes a comparison between horseradish peroxidase (HRP) and soybean peroxidase (SBP), the two most widely used commercial peroxidases for the removal of phenol from wastewater. Both enzymes achieve maximal removal efficiency in a neutral pH medium although they are still quite active in a pH range of between 6.0 and 8.0. The fact that both enzymes show similar phenol elimination levels at any temperature between 25 and 40 degrees C is also of interest. Studies were carried out in the absence and presence of different concentrations of a stabilisation additive, polyethylene glycol (PEG), in an attempt to optimise the phenol elimination procedure. The final choice of peroxidase will depend on the characteristics of the effluent, operational requirements and on economic considerations. Our findings show that HRP acts faster than SBP but is more susceptible to inactivation, although it is better protected by PEG. In consequence HRP will be the most suitable choice but the addition of a sufficient amount of PEG is critical.

Ultrafiltration membrane reactors for enzymatic resolution of amino acids: design model and optimization.

In this paper the possibility of continuous resolution of DL-phenylalanine, catalyzed by L-aminoacylase in a ultrafiltration membrane reactor (UFMR) is presented. A simple design model, based on previous kinetic studies, has been demonstrated to be capable of describing the behavior of the experimental system. The model has been used to determine the optimal experimental conditions to carry out the asymmetrical hydrolysis of N-acetyl-DL-phenylalanine.