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Figure 24. Gas phase bioreactor (Ushiyama, et al., 1984).

Figure 25. Photo introducing bioreactor (Ikeda, 1985).

Figure 25. Photo introducing bioreactor (Ikeda, 1985).

Gas Permeable Membrane Aerator Bioreactor. This type of bioreactor has not yet been fully developed. Nevertheless, some information is available. For example, one bioreactor is equipped with an aerator composed of fine tubes made of polycarbonate, polypropylene, silicone gum, etc. This type of bioreactor should be valuable for immobilized plant cell cultures.

3.5 Bioreactor Size

For industrial production of secondary metabolites, large scale bioreactor systems (sometime over 100 kl) will be required. The 75 kl and 20 kl bioreactor systems used for pilot scale experimentation are at present the largest in the world. They are at the DIVERSA Gesellschaft fiir Bio- und Verfahlenstechnik mbH in Germany and Nitto Denko Co., Ltd. in Japan. When there is a limited demand for a particular metabolite (e.g., a pigment), the production of commercial quantities can be done in the pilot scale bioreactor. Shikonin is produced this way. In 1983, Mitui Petrochemical Industries became the first to commercially produce a plant metabolite by using a 750 1 bioreactor. For routine experiments, the smaller bioreactors of vessel volume 1 to 100 liters are more widely used. Small bioreactors with volumes from 1 to 20 liters are used commercially for the production of clonal plants. These small bioreactors are valuable for the rapid propagation of large numbers of clonal plantlets. Through asexual embryogenesis, 10,000 to 1,000,000 embryos can be produced per liter and these embryos are then grown to plantlets. Using 2 to 10 1 bioreactors, it is also possible to produce 5,000 to 10,000 plantlets from plant tissue, which can then be transplanted directly into soil.

3.6 Culture Period

The growth of plant cells, tissues, and organs is much slower than microbial organisms. The most rapid growth cell line reported in scientific journals is the bright yellow Nicotiana tabacum cv. (Noguchi et al., 1987).[21] The doubling time of this cell strain was 15 h, and the duration to maximum growth was 80 h (3.3 days) when cultured in a 20 kl pilot scale bioreactor. In general, the growth of the cells of herbaceous annual plants is rapid and their doubling time is usually about 1 to 3 days (duration to maximum growth was 10 to 20 days), and that of woody plants or differentiated organs is slow (doubling time is about 2 to 10 days and the culture period is about 20 to 100 days).

3.7 Aeration and Agitation

The oxygen requirement of plant cells is quite low compared to microorganisms. Kato et al. (1975)[22] have examined the effect of kLa on biomass production (Fig. 26a). They observed that the volumetric oxygen transfer coefficient, kLa was constant after 10 h and the final biomass concentration became constant at 0.43 g cell dry weight/g sucrose. When kLa was set under 10 h, cell yield became dependent on kLa values. The effect of agitation speed on final cell mass concentration was also analyzed by Kato et al. (1975)[22] using a 15 1 bioreactor (Fig. 26b). At lower agitation speeds (less than 150 rpm), cell mass concentration became constant. However, when the agitation speed exceeded 150 rpm, the cultures became bulky and started to foam profusely. An agitation speed of either 50 or 100 rpm seemed to be optimal for production of cell mass and also for avoiding the culture problems.

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