Liquid fermentation

More than 90% of enzymes are produced by fermentation by microorganisms, which are used to prepare industrial and special use enzymes. Prokaryotic cells and eukaryotic cells can be easily grown in culture, and the technology of scale-up is well established on an industrial scale. Various kinds of fungi, bacteria and yeast have been screened for the production of special enzymes. Extracellular enzymes, for instance hydrolytic enzymes, are secreted into liquid and solid culture and are relatively stable in cultivation media. 

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Pathogens that are difficult to mass-produce offer a technological challenge. Many fungi such as Alternaria spp. and some Colle-totrichum spp. do not sporulate under liquid fermentation, the preferred method of commercial inoculum production. Labor-intensive... 

Liquid fermentation is useful for the production of enzymes as well as antibiotics. It is good for scale-up and reproduction. There are two types of enzyme produced intracellular and extracellular enzymes. With advances in genetic engineering, Escherichia coli is now being used to produce enzymes. When E. coli is used, the enzyme is accumulated inside the cell. This method is very popular. 

In Japan, solid fermentation is still used to produce many kinds of enzymes including lipases, proteases and acylases. Some glycotransferases are also produced by solid fermentation. In the production of proteases, solid fermentation is often used to increase the productivity in solids. On changing to liquid fermentation, the protease is not produced and its properties change. Solid fermentation is old-fashioned and difficult to scale up because of the expensive facilities needed. 

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. 

For example, in China, Timmins and Marter (1992) added sour liquid from a traditional fermentation process (liquid fermentate from peas or... 

Fig. 1. Comparison of typical solid-state fermentation (SSF) and submerged liquid fermentation (SLF) systems. A stirred-bed SSF bioreactor of the design of Durand and Chereau [2] is compared with a typical stirred SLF bioreactor. For each bioreactor an expanded view of the microscale is also shown, in order to highlight differences between the micro-structure of the two systems. The relative scales make it clear that mixing is possible on much smaller scales in SLF than in SSF, since in SSF mixing cannot take place at scales smaller than the particle size. Note that particle sizes in SSF are commonly larger than 1 mm...

Table 1. Comparison of solid-state fermentation and submerged liquid fermentation...

The bioreactor is the central point of a fermentation process. It is here that the biotransformation takes place, that a raw material is turned into a desired and valued product Optimization of the rate of formation and yield of product within the bioreactor is a key part of optimizing the production process. Although the field of bioreactor design for submerged liquid fermentation systems is well developed, many of the principles cannot be directly translated to SSF systems. Solid beds and liquid broths are different solid beds are not as easy to mix as liquid broths, and due to poor heat transfer properties of solid substrate beds, heat removal is much more difficult in SSF than it is in SLF. 

G2. [Note This problem is quite extensive.] Biorefineries producing ethanol by fermentation have several distillation columns to separate the ethanol from the water. The first column, the beer still, is a stripping column that takes the dilute liquid fermenter product containing up to 15% solids and produces a clean vapor product that is sent to the main distillation column. The main column produces a distillate product between about 65 mole % and the ethanol azeotrope, and a bottoms product with very litde ethanol. The calculated diameter of the main distillation column is much greater at the top than elsewhere. To reduce the size and hence the cost of the main column, one can use a two-enthalpy feed system split the vapor feed into two parts and condense one part, then feed both parts to the main column at their optimum feed locations. This method reduces the vapor velocity in the top of the column, which reduces the calculated diameter however, a few additional stages may be required to obtain the desired purity. 

Moreover, Crestini et al. (1996) reported that the yields of chitosan, viz., 120mg/L of fermentation medium under liquid fermentation conditions, and 6.18g/kg of fermentation medium under solid-state fermentation conditions are produced from the mushrotxn, L. edodes. Based on this data, it can be conad-ered that the cultivation of mushroom on solid support, which is the natural growing method of mushroom, might be the best cultivation method for the production of chitin and chitosan from mushrooms. The yield of extracted chitin and chitosan depends on mushroom species, harvesting time, and chitin and chitosan extraction processes and conditions (POchanavanich and Suntomsuk 2002, Yai and Man 2007a). 

EXAMPLE 1.7-1. Heating of Fermentation Medium A liquid fermentation medium at 30°C is pumped at a rate of 2000 kg/h through a heater, where it is heated to 70°C under pressure. The waste heat water used to heat this medium enters at 95°C and leaves at 85°C. The average heat capacity of the fermentation medium is 4.06 kJ/kg- K, and that for water is 4.21 kJ/kg K (Appendix A.2). The fermentation stream and the wastewater stream are separated by a metal surface through which heat is transferred and do not physically mix with each other. Make a complete heat, balance on the system. Calculate the water flow and the amount of heat added to the fermentation medium assuming no heat losses. The process flow is given in Fig. 1.7-1. 

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