Biocatalytic Synthesis of Polymeric Esters Used as Emulsifiers

Polyglycerol polyricinoleate (PGPR) is a polymeric ester widely used as emulsifier in the food industry. In this work, PGPR biocatalytic synthesis was carried out in a onestep solvent-free enzymatic process using lipase CALB immobilized in Lewatit® Monoplus<br /> MP 64 by adsorption. The optimal immobilization conditions were determined: initial<br /> enzyme concentration of 13 mg of Lowry protein per mL phosphate buffer pH 7, and<br /> ricinoleic acid as a support activator. An immobilized derivative with 35.93 ± 4.90 mg of<br /> Lowry protein per g of dry support was obtained. It was used as a catalyst for PGPR<br /> production in open air and vacuum batch reactors, and the results obtained showed that<br /> only when the reaction equilibrium was shifted towards ester production by means of water removal, the PGPR produced fulfilled the European legislation (acid value ≤ 6 mg of KOH per g of product).

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.