Fermentation Technologies
Fermentation-Microbes Immobilization - Stability Analysis

Immobilization of fermentation reactions microbes  has gained wide use and study, however, the variables are so many that proper organization of the properties are effective for supporting fermentation reactor designs and analyses. The motivation for the immobilization of microbes are many and includes, the ready separation of the microbes from the final product for continuous operations, enable the use of pathogenic microbes without the risk of pathogenic attacks, and to enable the design of more complex reactors that can overcome certain reaction limiting conditions. Remarkably the immobilization of microbes has followed the same technique as used for the immobilization of enzymes. However, the larger size of microbes has influenced the techniques.

Immobilized enzymes, however, were known to change their characteristics, stability and even kinetic properties; and immobilized microbes have also shown the same changes in characteristics and stability, and possibly even kinetic properties. The variations in the characteristics of immobilized microbes however are likely more than as is with enzymes, for one reason because the microbes still have the capability for growth. At a minimum the immobilization of microbes is impacted by several factors:

• immobilization method
• geometric Shape of microbe,
• geometric shape of immobilization substance,
• point of immobilization of microbes,
• length of the immobilization substance,

Each of these affects the performance because of the degree of solute penetrability that results after the immobilization, as can be surmised from the presentation below.

Immobilization Method
As for immobilized enzymes two broad types of methods have been used to immobilize microorganisms: attachment to a support and entrapment. The details of the types of immobilizations are as shown in Table 1 - Methods of Immobilization. The corresponding enzyme immobilization issues of these methods have been well-documented, except for biofilm formation which is unique to growth organisms as bacteria.

Currently the Biofilm formation as an immobilization seem most common with bacteria, and as a case where bacteria in the planktonic state are made to grow on an immobilization support specifically selected for the objective and therefore becoming a sessile colony of microbes, over which substrate broth can flow. The study and use of biofilm formations is of intense interest and study. 

However, for the specific issue being delineated presently with respect to solute penetrability of the immobilized microbes matrix, only the Attachment methods are of the greatest impact; and most of the

Geometric Shape of Microbes
The fermentation microbes have variety of shapes, and surface biochemical compositions and as such each one will  get immobilize to the immobilization in some preferred but unique orientation from the others, depending on the immobilization circumstance. Naturally this immobilization orientation variation will undoubtedly impact the solute penetrability characteristic of the specific microbe and hence impact the effectiveness of the immobilized microbe in carry out the oxidative consumption of of the substrates.

The shape is also critical particularly if the Plasma Membrane transporters of the microbe should have a preferred orientation and such orientation be such that the transporters are aligned away from the bulk Mash or broth. Then clearly the diffusion of the mash substances becomes critical in the performance of the microbes as a fermentation agent.

Geometric shape of Immobilization Substance
The immobilization substance geometry also will impact the performance of the microbes after the immobilization. Obviously straight lateral oriented substance that supports lateral immobilization will result in more packing than non-straight, even if, lateral oriented devices as such devices may prevent uniform one-to-one immobilization between the microbes and immobilization points on the device.

Point of immobilization of microbes
The point of immobilization also impacts the penetrability of the microbe matrix that results from the immobilization. As briefly observed above, the microbes if immobilized along an orientation that the forces the Plasma Membrane Transporter to face a direction away from the bulk of the broth, then such immobilized microbes may just perform sub-par.

However, there is even the more critical situation where the point of immobilization may be such as to stunt or inhibit growth of the microbes -- the form of growth being discussed here goes beyond individual cell enlargement in size but possibly cell division as well. Of course, stunted growth is the more serious of the two forms of impact from consideration.

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Length of the immobilization Substance
The length of the substance for the immobilization of the microbes also would affect the performance: Obviously when relatively lengthy substances are used, then the microbes just may be far away enough from the primary carrier to have a dynamic of wash as the substrate broth flows over the carrier. While this situation might completely eliminate the issue of penetrability, this method of immobilization just lead to leaching of microbes and thereby defeat the entire purpose of the immobilization.

Dangling Immobilization Issues
in comparison with enzyme immobilization, the immobilization of microbes raises the issue of microbes growth. One of two situation develops for consideration: The immobilization process must either prevent cell division growth of the microbes or support spontaneous immobilization of the microbes which could only be supported in the use of microbes that readily form biofilms.

The latter case of biofilm formation which requires stagnant broth for the fermentation obviously restricts the operation to batch fermentation reactors only. Evidently, the former case then offers more flexibility for reactor design apparently.

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