Seed fermentor

Specific procedures exist for storing (16,17) and propagating microorganisms to obtain reproducible fermentations. The stock culture is stored frozen (<—80°C) or freeze-dried. To prepare the inoculum (seed) mixture, an aUquot is taken and grown in consecutive soHd or Hquid cultures of increasing volume. The volume of the last step, the seed fermentor, is typically 4—12% of the main fermentor volume. 

The simple fermentor model has three state variables that change with time during the batch. The first is the concentration of cells X (grams of cells per liter of reactor liquid) that grow during the batch from some initial small value. This is provided by a seed fermentor that is itself a small batch fermentor in which a small number of cells are grown. 

Vessel Batch Reactor, fermentor, seed fermentor, airlift fermenter... 

Another recent trend in fermentation is the use of disposable bioreactors instead of stainless steel reactors for process development, especially in pharmaceutical manufacturing (Hanson et al., 2(X)9). Disposable bioreactors are typically plastic devices, such as microtiter plates, T-flasks, shake flasks and wave reactors, with different sizes. Disposable bioreactors can be used as a seed fermentor or as a production fermentor for products on a small scale (Mikola et al, 2007). The main advantages of disposable reactors include more flexibility in operation and use for different products, elimination of CTOss-contamination, less time needed to set up because the reactor is ready to use, low cost and less labor needed. However, disposable reactor sizes do not exceed 2,000L because of physical limitations, stabihty issues and heat and mass transfer limitations, as these reactors do not have impellers for mixing. In addition, disposable plastic reactors may leach chemical components into the media that could negatively impact the quahty of the final product (Hanson et al, 2009). 

Fig. 3.6 Human serum albumin (HSA) was produced during the sprouting of transgenic rape-seeds. A light-inducible Rubisco promoter was used to control transgene expression. The highest yield was obtained with light induction after three days of continuous darkness. Sprouting was carried out in an airlift fermentor at room temperature. The sprouting medium was water.

The medium is sterilized, cooled to 24 °C, and inoculated. After 24-hr seed growth, larger fermentors are seeded. Sterile air is sparged through the tank, at about one volume per volume per minute. The time of the production stage varies from 60 to 200 hr. 

Fermentation Conditions All juices had additions prior to fermentation in order to eliminate deficiencies from being a factor in hydrogen sulfide formation. These included 120 mg N/L in the form of diammonium phosphate (DAP), 50 mg/L S02, 75 ug/L pantothenate, 2 ug/L biotin and 75 ug/L thiamin. All fermentations were inoculated widi 240 mg/L of active dry wine yeast (Fermivin), that had been reactivated in 35°C water. All fermentations were conducted in duplicate at 25°C, in temperature controlled, constantly stirred (100 rpm), fermentors (Applikon) using 500 mL of white juice or 300 mL juice of red juice plus the corresponding amount of skins and seeds. 

Once the expression of the protein is optimized and seed stocks are made, the next step in production is their growth on a large scale to generate sufficient product. The scale of fermentation is determined by the therapeutic dose of the product, the total number of doses required, and the shelf-life of the product. The ideal characteristics of a bioreactor or a fermentor are listed in Table 3.3. 

The operating conditions for solid-state fermentation for cellulase production are dependent on the strain to be used, the reactor type and the medium composition, but the basic operating procedure remains the same as shown in Fig. 2. The final product can be obtained as crude solid cellulase, liquid cellulase or powder cellulase according to the application. Figure 3 shows a process flowsheet for cellulase production [25]. In the process, wheat bran is used as substrate. Seeds are prepared in a stirred-tank fermentor and then sprayed into the medium by a spray distributor. The fermentation is performed in a shallow-tray fermentor. The temperature and humidity in the fermentor are automatically regulated. After fermentation, cellulase is recovered by water extraction and purified by salt precipitation and ion exchange. The final product is concentrat-... 

---