Foaming and cell flotation in suspended plant cell cultures and the effect of chemical antifoams

Abstract

Foam development and stability in Atropa belladonna suspensions were investigated as a function of culture conditions. Foaming was due mainly to properties of the cell-free broth and was correlated with protein content; effects due to presence of cells increased towards the end of batch culture. Highest foam levels were measured 11 days after inoculation. Air flow rate was of major importance in determining foam volume; foam volume and stability were also strongly dependent on pH. Foam flotation of plant cells was very effective. After 30 min foaming, ca. 55% of cells were found in the foam; this increased to ca. 75% after 90 min. Polypropylene glycol 1025 and 2025, Pluronic PE 6100, and Antifoam-C emulsion were tested as chemical antifoams. Polypropylene glycol 1025 and Antifoam C at concentrations up to 600 ppm had no adverse effect on growth in shake flasks; Pluronic PE 6100 has an inhibitory effect at all levels tested. Concentrations of polypropylene glycol 2025 and Pluronic PE 6100 as low as 20 ppm reduced foam volumes by a factor of ca. 10. Addition of antifoam reduced k(L)a values in bubble-column and stirred-tank bioreactors. After operation of a stirred reactor for 2 days using Antifoam C for foam control, cell production was limited by oxygen due to the effect of antifoam on mass transfer. Theoretical analysis showed that maximum cell concentrations and biomass levels decline with increasing reactors working volume due to greater consumption of antifoam to prevent foam overflow. The results indicate that when chemical foam control is used in plant cell cultures, head-space volume and tolerable foam levels must be considered to optimize biomass production. (c) 1994 John Wiley & Sons, Inc.

The accumulation of isocamptothecin A and B in suspension cell culture of Camptotheca acuminata

“…When plant cells are cultured in bioreactors, foam buildup is a common phenomenon, especially in the late phase due to the excretion of metabolites such as proteins, peptides, and polysaccharide into the medium by aged cells (Wongsamuth and Doran, 1994). Adverse effects of foaming include reduction in the working volume of the bioreactor, contamination from foam overflow, and loss of productivity; thus, elimination of foaming has become a key consideration for large-scale culture of plant cells in bioreactors.…”

Bioreactor engineering for recombinant protein production in plant cell suspension cultures

“…Approaches to reduce the foaming include (1) reducing agitation speed and aeration rate without significantly impacting mixing intensity and mass transfer rates [138], (2) adding antifoam reagents leading to a reduction of the surface tension of the culture broth [139], (3) applying surface aeration or bubble free-aeration [140], and (4) using a mechanical foam breaker or installing an impeller above the culture broth to serve as a mechanical foam breaker. The application of antifoam reagents, which are added directly to the medium prior to inoculation (0.01% of working volume) and/or as required during cultivation, is the most common method [138,141]. Although Table 5 Bioreactor operation strategies for improving recombinant protein production using plant cell suspension cultures.…”

Gas Holdup in Bioreactors

“…The first is the dispersion of bubbles in the bulk of the culture, where bubbles rise relative to the liquid. The other is the foam that most often develops on top of the culture (1)(2)(3). Again, foam consists of gas dispersed within the continuous liquid phase, even though the gas bubbles no longer rise relative to the liquid.…”

“…It is essentially determined by the diffusion of oxygen across the liquid-side boundary layer around the bubbles, which is driven by the oxygen concentration difference O * −O between the bulk concentration O and the concentration O * directly at the physical interfacial area. With the corresponding volumetric transfer coefficient k L a, the corresponding transport law, the oxygen transfer rate (OTR) reads as given in Equation 3:…”