Fermentation Technologies
Fermentation Physics and Biophysics - Fundamentals

Every person whether growing into biotechnology science or developing skills in biotechnology of any kind, with the object of producing alcohol, needs to understand the basics of the physics and biophysics of fermentation, but more so when the person desires to engage in the design and operation of Fermentation Reactors. 

A simple review of the literature on Biotechnology or biochemical engineering reflects a vast amount of research work that has been undertaken in the field. Further, examined within the context of the objectives for the conduct of each research, the results of each reflect superb work. However, for the purposes of reactor engineering, the published works must be reviewed within the context of the demands of such design objectives; and for the purposes of the analysis undertaken here, a perspective has been adopted with respect to the packaging of the physics and biophysics fundamentals of the fermentation.

Fermentation reaction is a component of the catabolic reactions; and so for the purposes of efficacious reactors design then the reaction mechanism of fermentation must be fully defined to the end of deriving the applicable kinetic rate equations. Summarily the physics of fermentation process as adopted entails the

• convection cum chemical potential gradient-driven diffusion of a collection of substances within a matrix termed "Mash" or "Broth" of different concentrations to the surface of a yeast cell,
• the transport of these substances through the plasma membrane transporters into the interior of the cell,
• the occurrence of metabolic reactions including the biochemical fermentation reaction based on these substances,
• and the discharge into the cell-external by the cell of the products of the metabolic reactions.

A very important aspect of this presentation that needs notice is that the term fermentation is used with a dual meaning to some extent. First, fermentation is accurately use to reflect purely the biochemical reaction, termed fermentation, to the exclusion of the mass transfer and diffusion of the reactants and products of the biochemical fermentation reaction. Second fermentation is used in the sense of reactor designer to mean first usage together with the sum total of all the mass transport phenomenon.

Preferably, though rather simplistic, the reactor designer usage of the term fermentation is adopted for the purposes here, because it enables an organizing of the engineering science issues  involved, and allows every prospective user of the results of our analysis to better utilize the results with respect to equipment operations controls.

Then, of course, there are the straight physics issues divorced from the cell interactions: There is the impact of the rate of diffusion of the expel-products away from the yeast environment on the rate of diffusion of the substances to the microbe, and hence the rate of fermentation; There exists the potential dependence of the metabolic rate of consumption of substances on the presence as well as on the concentration of another substance.

Metabolic reactions occur inside the cytoplasm of the microbes, and as such for the fermentative oxidative degradation of the substrate to occur the substrate and the nutrients must be absorbed through the microbial membrane into the cellular matrix, the cytosol or cytoplasms, of the microbe. This transportation of substrates and nutrients is accomplished by the Transporters and Symporters. The metabolic process begins with the Transporters and Symporters transferring the substrates and the nutrients ions into the cytoplasm of the microbe cell.

The specifics of the metabolic reactions involving fermentation, often termed biochemical pathway, however, is dependent on the microbe and the substances mix. Generally the pathway entails the fermentative utilization of sugar to pyruvate followed by the reoxidation of pyruvate by  [biochemical] fermentation.

However, the Mash in virtually all cases may consist of such common components as these include carbon oxygen, nitrogen and hydrogen; to leaser extent quantities of phosphorus, sulfur, potassium, and magnesium must also be provided for the synthesis of minor components; and minerals (i.e. Mn, Co, Cu, Zn) and organic factors (amino acids, nucleic acids, and vitamins) are required in trace amounts. The relative requirements for nutrients not utilized in ethanol synthesis are in proportion to the major components of the microbe cell.

Further, generally most microbes metabolize most sugar to ethanol under anaerobic conditions, none the less, small concentration of oxygen must be provided to the fermenting yeast, oxygen being a necessary component in the  biosynthesis of

 In a detailed analysis, such as is usually required for engineering design needs, all these interactions needs to be accounted for. The reaction engineering analysis must embody the summation of the effects of the diffusive transport of the substrates and nutrients to the cell-wall, the rate and efficiency of the Plasma Membrane Transporters and Symporters, the kinetics and rate of the operational Biochemical Pathways, and the diffusive effects of the fermentation products and by-products. 

Moreover, the deployment of these microorganism in the operation of a biochemical reactor can be carried out in one of two ways: homogenous suspension and immobilized suspension; and each approach has its advantages and disadvantages in the design process. Hence, the reaction engineering analysis should also consider the effects of mixing heterogeneity in the case of homogeneous reactors, and microbes immobilization such as stability analysis, kinetic modification analysis and microbes-growth impact analysis. Also to be factored in the analysis is the possibility that the substances can suffer both independent and dependent variations; though the former variation is always at the discretion of the fermentation reactor designer.

  Company