FOAMING AND CELL FLOTATION IN SUSPENDED PLANT-CELL CULTURES AND THE EFFECT OF CHEMICAL ANTIFOAMS

Foam development and stability in Atropa belladonna suspensions were i nvestigated as a function of culture conditions. Foaming was due mainl y to properties of the cell-free broth and was correlated with protein content; effects due to presence of cells increased toward the end of batch culture. Highest foam levels were measured 11 days after inocul ation. Air flow rate was of major importance in determining foam volum e; 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 Anti foam-C emulsion were tested as chemical antifoams. Polypropylene glyco l 1025 and Antifoam C at concentrations up to 600 ppm had no adverse e ffect on growth in shake flasks; Pluronic PE 6100 had an inhibitory ef fect at all levels tested. Concentrations of polypropylene glycol 2025 and Pluronic PE 6100 as low as 20 ppm reduced foam volumes by a facto r of ca. 10. Addition of antifoam reduced k(L)a values in bubble-colum n and stirred-tank bioreactors. After operation of a stirred reactor f or 2 days using Antifoam C for foam control, cell production was limit ed by oxygen due to the effect of antifoam on mass transfer. Theoretic al analysis showed that maximum cell concentrations and biomass levels decline with increasing reactor working volume due to greater consump tion of antifoam to prevent foam overflow. The results indicate that w hen chemical foam control is used in plant cell culture, head-space vo lume and tolerable foam levels must be considered to optimize biomass production. (C) 1994 John Wiley and Sons, Inc.