Physical parameters to consider when choosing enzyme carriers

Extensive experience from chromatography resins has been transferred into the synthesis and use of enzyme carrier resins. Also, as per S. Cantone; Chem Soc Rev, polymeric carriers offer a very wide selection of properties for finding a tailored match to the enzyme and process. Commercial polymeric resins is likely the easiest and most convenient way of immobilizing enzymes. Entirely synthetic and polymers of natural origin, such as agarose, chitosan, cellulose, albumin, are all available commercially (Cantone et al. 2013). Thus, opting for the right physical parameters is important.

When working with an enzyme carrier, deciding on physical parameters is a big challenge. Here is an insight that discusses the parameters to consider when choosing the right enzyme carrier. A wide range of available compounds can be successfully used as enzyme carriers.

The criteria of the choice suitable enzyme carrier for a given enzyme and its application include:

  1. The cost and availability.
  2. Stability (or reactivity if necessary) in specific conditions.
  3. Type of reactor.
  4. Physicochemical parameters of the carrier must be considered.

In general, the carriers used for enzyme immobilization by adsorption can be divided into both organic and inorganic origins. The most common inorganic carriers are

  • silicas
  • titania
  • hydroxyapatite.

The organic carriers, by contrast, include compounds of natural origin, such as

  • chitin
  • chitosan
  • cellulose
  • alginate

as well as synthetic compounds, mainly polymers such as

  • polystyrene
  • acrylates
  • methacrylates

The advantage of these matrices is that they can be readily chemically modified to match conditions for a given enzyme and its application. But before a decision certain parameters need to be considered when working with immobilized enzymes.

Parameters to be considered


                                                       Figure: Enzyme and carrier 

Image: Miletić N, Vuković Z, Nastasović A, Loos K., Effect of Candida antarctica Lipase B Immobilization on the Porous Structure of the Carrier

When deciding on a carrier to immobilize an enzyme on, one must consider

  • particle size
  • chemical composition
  • surface chemistry
  • pore size
  • porosity
  • pore size distribution
  • morphology
  • mechanical stability

Given a fixed total mass of carrier, a smaller particle size provides a larger surface area for immobilization than larger particles. Given a fixed particle size, using porous particles allows for a larger surface area. However, given porous particles of a fixed total mass, smaller particles still provide a larger surface area for immobilization. The explanation stems from the fact that immobilized are unevenly distributed and concentrated primarily in the carrier particle's outer layers.

The consequences of using small particles are that the separation from the reaction medium may be more difficult, the sedimentation rate slower, and that pressure drop through fixed bed (column) reactors and, to a minor extent, rotating bed reactors. The flow resistance through a packed bed depends on the parameters of the liquid phase and its velocity through the bed as well as the particle size and void fraction of the bed.

These are the same parameters that one would like to optimize when immobilizing enzymes in the material, i.e. to maximize surface area and minimize diffusion resistance. A balance will have to be struck.

Reusing enzymes and issues

The recyclability and long-term operation of an immobilized enzyme is very dependent on enzyme stability and process and storage conditions. However, sufficient mechanical stability is also a requirement. Materials that break under the process conditions will result in fines and problems in the downstream processing.

The crux is that the mechanical strength of a particle is related to its size, morphology, and porosity. Thus, pore size, pore size distribution, and pore geometry directly influence the mechanical strength of the particle the larger the pore, the more friable the material.

Use of RBR

Notably, when working with an enzyme carrier, the pressure drop across a packed bed can be hundreds of bars, which affects the stability. But the pressure drop across a rotating bed reactor (RBR) is a fraction of a bar and the process conditions in an RBR are much gentler to the particles compared to a packed bed. This allows for the use of much softer and friable particles. Thus, with the use of RBR, reusing of immobilised emzymes is possible with more stability and mechanical strength.

Here are some examples of the application of RBR with immobilized enzymes:

  1. Biocatalysis by immobilized enzymes in a rotating bed reactor
  2. Enzyme immobilization screening using magnetic rotating bed reactors

Interested in the rotating bed reactor?  Let SpinChem help you understand how the rotating bed reactor technology can simplify or improve your process. Get in touch with us today to get started towards better, more efficient biocatalysis.

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