Biocatalytic membranes

An important problem in emulsified organic-aqueous systems is that of scale-up, which is concerned with the realization of stable emulsions and the separation of phases after the reaction. The use of biphasic membrane systems that contain the enzyme and keep the two phases separated is likely to solve this problem. In the case of 5-naproxen an ee of 92% has been demonstrated without any decay in activity over a period of two weeks of continuous operation. A number of examples of biocatalytic membrane reactors have been provided by Giorno and Drioli (2000) and include the conversion of fumaric acid to L-aspartic acid, L-aspartic acid to L-alanine, and cortexolone to hydrocortisone and prednisolone. 

Biocatalytic membrane electrodes have an ISE or a gas sensing electrode in contact with a thin layer of biocatalytic material, which can be an immobilized enzyme, bacterial particles or a tissue slice, as shown in Fig. 3 The biocatalyst converts substrate (the analyte) into product, which is measured by the electrode. Electrodes of this type are often referred to as biosensors . 

A representative example of a biocatalytic membrane electrode is an electrode for L-arginine The bacterium streptococcus faecium is immobilized on the gas permeable membrane of an ammonia electrode. Arginine deiminase in the bacterium catalyzes the following reaction... 

The concept of a biocatalytic membrane electrode has been extended to the use of a tissue slice as the catalytic layer. An example of this approach is an electrode for AMP which consists of a slice of rabbit muscle adjacent to an ammonia gas electrode. NHj is produced by enzymatic action of rabbit muscle constituents on AMP The electrode exhibits a linear range of 1.4 x 10 to 1.0 x 10 M with a response time varying from 2.5 to 8.5 min, depending on the concentration. Electrode lifetime is about 28 days when stored between use in buffer with sodium azide to prevent bacterial growth. Excellent selectivity enables AMP to be determined in serum. 

Giomo, L. and Drioli, E. (2000) Biocatalytic membrane reactors applications and perspectives. Trends in Biotechnology, 18, 339-349. 

The method of enzyme immobilization constitutes a key factor in the construction of these systems as it is the biocatalytic membrane that largely determines sensitivity, stability and response-time characteristics of the biosensor. 

CiucuA,MareaurV,FlexhinS,Lucaciul, David F (1991) Biocatalytic membrane electrode for phenol. Anal Lett 24 567 - 580... 

Drioli, E. and Giorno, L. (1999) Biocatalytic Membrane Reactors Application in Biotechnology and the Pharmaceutical Industry, Taylor Francis Publisher, Padstow, UK. 

The performance of a hollow-fiber or sheet bioreactor is primarily determined by the momentum and mass -transport rate [15,16] ofthe key nutrients through the biocatalytic membrane layer. Thus, the operating conditions (transmembrane pressure, feed velocity), the physical properties of membrane (porosity, wall thickness, lumen radius, matrix structure, etc.) can considerably influence the performance of a bioreactor, the... 

Applications of whole-cell biocatalytic membrane reactors, in the agro-food industry and in pharmaceutical and biomedical treatments are listed by Giorno and Drioli [3], Frazeres and Cabral [9] have reviewed the most important applications of enzyme membrane reactors such as hydrolysis of macromolecules, biotransformation of lipids, reactions with cofactors, synthesis of peptides, optical resolution of amino acids. Another widespread application of the membrane bioreactor is the wastewater treatment will be discussed in a separate section. 

A solution methodology of the above, a nonlinear differential equation, will be shown. In essence, this solution method serves the mass-transfer rate and the concentration distribution in closed, explicit mathematical expression. The method can be applied for Cartesian coordinates and cylindrical coordinates, as will be shown. For the solution of Equation 14.2, the biocatalytic membrane should be divided into M sublayers, in the direction ofthe mass transport, that is perpendicular to the membrane interface (for details see e.g., Nagy s paper [40]), with thickness of A8 (A8 = 8/M) and with constant transport parameters in every sublayer. Thus, for the mth sublayer ofthe membrane layer, using dimensionless quantities, it can be obtained ... 

The main applications of biocatalytic membrane reactors in the food sector include reduction of the viscosity of juices by hydrolyzing pectins, reduction of the lactose content in milk and whey by its conversion into digestible sugar, treatment of musts... 

Biocatalytic membrane readors are also used for the treatment of musts and wines by the conversion of polyphenolic compounds and anthocyanes. Laccase is used to oxidize polyphenols in solution and anthodanase is used immobilized on synthetic and natural polymers to hydrolyze anthocyanes. 

FIGURE 6.30 Concepts of biocatalytic membrane reactors with (a) non-immobilized or (b) immobilized enzymes. 

Rios GM, Belleville MP, Paolucci D, and Sanchez J. Progress in enzymatic membrane reactors. J. Membr. Sci. 2004 242 189-196. Giomo L and Drioli E. Biocatalytic membrane reactors applications and perspectives. Tibtech 2000 18 339-349. 

Biocatalytic membrane electrodes significantly expand the scope of direct potentiometry by enabling biosensors that respond to a whole host of organic substrates to be made. The selectivity of these sensors is a combination of the selectivity of the biocatalyst for the substrate and the ISE for other constituents in the sample that might reach the ISE surface membrane. Thus, the selectivity with respect to other organic constituents in the sample is determined by biocatalyst... 

Renneberg et al. (1984) described a microbial hybrid sensor for a-amylase assay. A membrane with coimmobilized B. subtilis cells and glucoamylase was attached to an O2 electrode. Starch and the a-amylase sample were added to the measuring cell. Low-molecular weight products of the a-amylase-catalyzed starch hydrolysis diffuse into the biocatalytic membrane where they are cleaved by glucoamylase to glucose, which is assimilated by the bacteria. The sensor responded linearly to a-amylase up to 1.5 U/ml. 

---