THE IMPORTANCE OF FOAMS AND ANTIFOAMING IN BIOPROCESSES

Abstract

Foams are comprised of thousands of tiny bubbles of mechanical or chemical origin and are
generated within a liquid. If these bubbles rise and accumulate at the liquid surface faster than they
decay, foaming occurs. Foams are defined as a dispersion of gas in liquid (>95% gas) when the
distance between individual bubbles is extremely small and the volume fraction of gas is quite large.
The presence of foams in products or processes may or may not be desirable. Foaming occurs during
fermentations, which is considered undesirable and is a problem common to many of microbial
fermentations, especially where surface active microbial products (bio-surfactants) are involved.
Foaming reduces the productive volume, i.e. increasing process costs, and can lead to blockage of
the outlets and threat the sterility of a fermenter.
Antifoam action may take the form of addition of antifoam agent, mechanical agitation or
ultrasound. The most commonly used method is the addition of chemical antifoams although it can
add significantly to process costs and reduce the oxygen transfer rate. That may also exert adverse
effects on the cell’s physiology.
Conversely, foam separation techniques can be used for the recovery of proteins. In addition,
foam fractionation has been successfully applied for the effective separation of surfactants and
biological materials such as proteins, microorganisms, suspended solids, aromatic substances and
pigments. It is, therefore, important to be able to effectively monitor and control the dynamic
formation and collapse of such foam phases. At last, in spite of the important role of foaming in
bioprocesses, successful prediction of foaming and defoaming phenomena is not entirely possible at
present and further attention and research continues to be needed