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  • Author or Editor: Chiao-Po Lin x
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This study was initiated to solve the problem of wall effect and dissolved oxygen (DO) encountered during establishing a scale-up process of lettuce suspension culture in a fermentor. The wall effect could result in as high as 10% loss of inoculum within 24 hrs. The main reason causing wall effect was identified as foam formed from the interaction of air bubble and inoculum. Bubble isolation by a screen column could successfully solve the wall effect. The effect of dissolved oxygen was then investigated. The plantlet regeneration was increased as dissolved oxygen increased from 20% to 80%. The relationship among agitation and aeration rate as well as oxygen concentration in the air was discussed.

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A scale-up process of lettuce (Lactuca sativa L.) suspension culture in a 2-liter bioreactor was investigated. Factors that influenced cell growth and differentiation, including foaming, the wall effect (inoculum adhering onto the vessel wall above the medium level), aeration, and dissolved oxygen (DO), were tested. The wall effect resulted in severe inoculum loss (10%) in 24 hours. Inoculum loss significantly decreased shoot regeneration. The wall effect was caused by two factors: 1) foaming caused by the interaction between air bubbles and inoculum, and 2) the bubbles produced by aeration. Foaming could be prevented by sieving the inoculum through a 400-pm screen filter and then rinsing the inoculum thoroughly with distilled water to remove single cells, cell debris, and the contents of broken cells. The wall effect caused by air bubbles could be prevented by putting a 150-μm screen column in the center of the bioreactor to isolate the aeration area from the inoculum. After the wall effect was removed, shoot regeneration in the bioreactor increased significantly to a level similar to that in 125-ml flasks at an aeration rate of 1 to 2 vvm (liters air/liters medium per rein). DO for this shoot regeneration level was ≈ 70% to 80%of saturation at the end of bioreactor culture.

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