Biocatalysts engineering by varying the binary CNTs-silica composition and the physicochemical characteristics of adsorbents for the immobilization of recombinant T. lanuginosus lipase.

Biocatalytic engineering was carried out by varying monotonically the binary CNTs-silica composition and, accordingly, the physicochemical characteristics of adsorbents developed for immobilization of recombinant T. lanuginosus lipase (rPichia/lip). The adsorbents based on composite carbon-silica materials (CCSMs) were produced by impregnating finely dispersed multi-walled carbon nanotubes with silica hydrosol followed by calcination in argon at 350°C; the mass ratio of the hydrophobic and the hydrophilic components varied over a wide range. Biocatalysts (BCs) for green low-temperature synthesis of various esters in a non-aqueous medium of organic solvents were prepared by adsorption of rPichia/lip with subsequent drying under ambient conditions. The characteristics of the CCSMs and BCs were characterized by thermogravimetry, nitrogen porosimetry and electron microscopy. The catalytic properties of BCs, such as enzymatic activity, substrate conversion and specificity, as well we their operational stability depending on the chemical composition of CCSMs were extensively studied in the esterification of saturated monocarboxylic acids (C4, C7, C18) and primary aliphatic alcohols (C2, C4, C16) in hexane at 20°C. It was found that the esterifying activity manyfold decreased with increasing the silica content primarily due to a decrease in adsorption ability of CCSMs toward rPichia/lip. The substrate specificity and operational stability of the lipase-active BCs did not greatly depend on the composition of CCSMs. Biocatalysts retained more than half of their initial esterifying activity after 10 reaction cycles.

Immobilization of glucoamylase by adsorption on carbon supports and its application for heterogeneous hydrolysis of dextrin.

Glucoamylase (GA) was immobilized by adsorption on carbon support: on Sibunit, on bulk catalytic filamentous carbon (bulk CFC) and on activated carbon (AC). This was used to prepare heterogeneous biocatalysts for the hydrolysis of starch dextrin. The effect of the texture characteristics and chemical properties of the support surface on the enhancement of the thermal stability of the immobilized enzyme was studied, and the rates of the biocatalyst's thermal inactivation at 65-80 degrees C were determined. The thermal stability of glucoamylase immobilized on different carbon supports was found to increase by 2-3 orders of magnitude in comparison with the soluble enzyme, and decrease in the following order: GA on Sibunit>GA on bulk CFC>GA on AC. The presence of the substrate (dextrin) was found to have a significant stabilizing effect. The thermal stability of the immobilized enzyme was found to increase linearly when the concentration of dextrin was increased from 10 wt/vol % to 50 wt/vol %. The total stabilization effect for glucoamylase immobilized on Sibunit in concentrated dextrin solutions was about 10(5) in comparison with the enzyme in a buffer solution. The developed biocatalyst, 'Glucoamylase on Sibunit' was found to have high operational stability during the continuous hydrolysis of 30-35 wt/vol % dextrin at 60 degrees C, its inactivation half-time (t1/2) exceeding 350 h. To improve the starch saccharification productivity, an immersed vortex reactor (IVR) was designed and tested in the heterogeneous process with the biocatalyst 'Glucoamylase on Sibunit'. The dextrin hydrolysis rate, as well as the process productivity in the vortex reactor, was found to increase by a factor of 1.2-1.5 in comparison with the packed-bed reactor.