Liquid Fermentation Process

FIGURE 10.5 Flowchart of the sponge-dough baking process for the production of pan bread and related products. 

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Buns and Rolls. Hamburger and hot dog buns and rolls may be processed in a manner directly analogous to those used for bread production. Almost all domestically produced bun products are produced by a batch liquid ferment process. After mixing, doughs are immediately divided and rounded to small unit-sized balls. Following a brief rest, these are given their final shape, proofed, baked, cooled, and packaged. 

Manufactured by the liquid-phase oxidation of ethanal at 60 C by oxygen or air under pressure in the presence of manganese(ii) ethanoate, the latter preventing the formation of perelhanoic acid. Another important route is the liquid-phase oxidation of butane by air at 50 atm. and 150-250 C in the presence of a metal ethanoate. Some ethanoic acid is produced by the catalytic oxidation of ethanol. Fermentation processes are used only for the production of vinegar. 

FIG. 18-28 Usually, the gas-liquid mass-transfer coefficient, K, is reduced with increased viscosity. This shows the effect of increased concentration of microbial cells in a fermentation process. 

In spite of its wide application, the mechanisms of this reaction remain obscure. Many diverse arguments have been published since the reaction was first investigated in 1897 (Bl, C5, C9, F7, J6, M5, P9, R2, S5, W2, W4, Yl, Y4). Cooper et al. (C9) introduced this method as a yardstick for the measurement of volumetric mass-transfer coefficients in gas-liquid contacting. Karow et al. (Kl) later concluded that the sulfite oxidation is suitable for fermentation process scale-up studies. Cooper et al. established that the reaction proceeds at a rate independent of sulfite ion concentration over wide concentration ranges. In their work they considered the sulfite oxidation to be of zero order with respect to both sulfite and sulfate concentration. 

The four antigens are produced in a fermentation process using the yeast Saccharomyces cerevisiae grown in chemically defined media. The purified antigens are formulated in aluminum-containing adjuvant in sterile liquid suspension. 

Advances in knowledge of the chemistry of fermentation processes will aid the exploitation of biomass energy, e.g. a more concentrated fermentation process for the production of sugar from cellulose is required if alcohol from Canada s very extensive forests is to compete with other sources of liquid fuel. 

Cultivation. The cells are transferred from the cryogenic cell bank to a liquid nutrient medium, where they are allowed to reproduce. Mammalian cells such as CHO divide about once every 24 h (bacterial cells, such as Escherichia coli, usually divide once every 20 min, and thus a sufficient number of cells are obtained in a much shorter time than in traditional fermentation processes). During the growth phase the cell culture is transferred to progressively larger culture vessels. 

There are many applications where it is necessary to monitor very low rates of flow (e.g. addition of mercaptans to natural gas in the gas industry or of anti-foaming agents to fermentation processes in the pharmaceutical industry). A low flow is considered to be of the order of 100 mm /s and an ultra-low flow of around 0.1 mm3/s for both liquids and gases. Table 6.2 includes commonly accepted minimum measurable rates of flow for types of flowmeter normally employed for this purpose02 . 

Fermentation gives rise to at least a two-phase system including the fermentation liquid mixture and the solid microorganisms that catalyze the fermentation process. Fermentation can also have three phases such as for aerobic fermentation where gaseous oxygen is bubbled through the fermentor. And immobilized packed-bed aerobic fermen-... 

Generally, the fermentation process involves the addition of a specific culture of microorganisms to a sterilized liquid substrate or broth in a tank (submerged fermentation), addition of air if aerobic, in a well-designed gas-liquid contactor. The fermentation process is then carried out to grow microorganisms and to produce the required chemicals. Table 11-1 lists examples of the processes used by fermentation. 

The fermentation process can be performed batch-wise or continuously at a given temperature and time. The broth is further processed to remove the desired chemical. Figure 11-11 shows a schematic and an abstracted physical model of a fermenter with the liquid phase as the control region. 

Gas/liquid contacting is frequently encountered in chemical reaction and bioprocess engineering. For reactions in gas/liquid systems (oxidation, hydrogenation, chlorination, and so on) and aerobic fermentation processes (including biological waste water treatment), the gaseous reaction partner must first be dissolved in the liquid. In order to increase its absorption rate, the gas must be dispersed into fine bubbles in the liquid. A fast rotating stirrer (e.g. a turbine stirrer), to which the gas is supplied from below, is normally used for this purpose (see the sketch in Fig. 34). 

Pitch-blade turbine (paddle stirrer with pitched blades) and propeller stirrers provide high mixing with an axial flow pattern. Both of these stirrers are normally used for low-viscosity liquids and in vessels with baffles. They are well suited for providing liquid homogenization and suspension of solids in slurry reactors. The stirrers can also be used in viscous fluids and for vessels with H/dT > 1, which are generally encountered in fermentation processes. For these situations, axial flow is increased with the use of multistage stirrers with pitched stirring surfaces. 

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