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g dry weight [¡J metabolite Q dry weight B metabolite yield productivity

Figure 19. Comparison of yield and productivity for cell mass and anthraquinones in various bioreactor systems. (1) Shake Flask. (2) Flat Blade Turbine. (3) Perfolated Disk Impeller. (4) Draft Tube Bioreactor with Kaplan Turbine. (5) Air-lift Bioreactor.

Figure 19. Comparison of yield and productivity for cell mass and anthraquinones in various bioreactor systems. (1) Shake Flask. (2) Flat Blade Turbine. (3) Perfolated Disk Impeller. (4) Draft Tube Bioreactor with Kaplan Turbine. (5) Air-lift Bioreactor.

Air Driven Bioreactors. The simplest design is the air-driven bioreactor equipped with sparger at the bottom of the vessel. It is widely used for plant cell, tissue, and organ cultures. In cases where the cells grow rapidly and the cell mass occupies 40-60% of the reactor volume, the flow characteristics become non-Newtonian and the culture medium can no longer be agitated by simple aeration.

Rotating Drum Bioreactor. The rotating drum bioreactor (Fig. 21) turns on rollers and the oxygen supply mechanism is entirely different from either the mechanically agitated or the air-lift bioreactor. Tanaka et al., (1983),[14] reported that the oxygen transfer coefficient is affected by a change of airflow rate under all rotational speeds (Fig. 22). This characteristic is suitable not only for the growth of plant cell, tissue, and organs but also for the production of metabolites under high viscosity and high density cultures. It is superior to the cultures using either mechanically agitated or air-lift bioreactors since the cultures are supplied ample oxygen and are only weakly stressed. Recently a 1 kl bioreactor of this type was constructed and used for a pilot scale experiment (Tanaka 1987).[15]

baffle oxygen plate sensor

Revolving Drum Bioreactor

Figure 21. Schematic diagram of the rotating drum bioreactor (Tanaka, H., et al., 1983)

Figure 20. Ninety-five liter automated bioreactor for plant cell, tissue and organ cultures. (Photo courtesy of K. F. Engineering Co., Ltd., Tokyo).

baffle oxygen plate sensor

Figure 21. Schematic diagram of the rotating drum bioreactor (Tanaka, H., et al., 1983)

AIR FLOW RATE (wm)

Figure 22. Effect of the airflow rate on kL a in rotating drum fermenter. (Tanaka, H., et al., 1983)

AIR FLOW RATE (wm)

Figure 22. Effect of the airflow rate on kL a in rotating drum fermenter. (Tanaka, H., et al., 1983)

Spin Filter Bioreactor. This type of bioreactor (Styer, 1985)[16] is equipped with a filter driven by a magnetic coupling in the stir plate (Fig. 26). This spinning filter operates as a medium agitator without generating shear stress and also serves as an excellent filter for the removal of the medium from the bioreactor without the cells plugging it. The spin filter bioreactor will be most suitable for the continuous culture of plant cells. When a conventional bioreactor was used and the feeding rate of the medium was increased, the cell density was decreased because of washout. However, when a spin filter bioreactor was used, the cell density was maintained constant and half of the spent medium was effectively removed through the spin filter.

Gaseous Phase Bioreactor. As shown in Fig. 24, this type of bioreactor is equipped with filters on which the culture is supported and with a shower nozzle for spraying on the medium (Ushiyama et al., 1984;[17] Ushiyama, 1988).1181 Seed cultures are inoculated on the filters and the medium is supplied to the culture by spraying from a shower nozzle. The drained medium is collected on the bottom of the bioreactor. This type of bioreactor is excellent for plant cell, tissue, and organ cultures because there is no mechanical agitation (e.g., driven impeller, aerator) and, therefore, the growth rate and the secondary metabolite production are enhanced.

Light Introducing Bioreactor. Plants are susceptible to light irradiation and as a consequence various metabolic and/or physiological changes are generated. Some important reactions are: (i) photosynthesis, (ii) activation of specific enzymes such as phenylalanine ammonia lyase (PAL) and to induce the production of flavonoids or anthodyanins, (iii) photomorphogenesis such as development of leaves. For these reactions, the introduction of light into the bioreactor is required. Inoue (1984)[19] reported a bioreactor equipped with transparent pipes. The light was emitted from the surface of the pipe into the bioreactor. Ikeda (1985)[2°1 reported an air-lift bioreactor equipped with a photo introducing draft tube (Fig. 25). The draft tube was constructed as an airtight tube which consisted of a transparent inner and outer tube. Within the center of the draft tube was a light introducing optical fiber. The light source was a sunlight collector system which operated automatically by computer control and the collected light was introduced into the bioreactor through the optical fibers. Introduction of light into the bioreactor will become an important technique for the production of specific plant metabolites.

spent medium air air

medium

> spent medium and cells

Spin Filter Bioreactor

sparger

Figure 23. The spin filter bioreactor (Styer, 1985).

sparger

Figure 23. The spin filter bioreactor (Styer, 1985).

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