DefinePK

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 microbialfermentations, 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