Polyhedral foams offer large gas-liquid interfacial area associated with a small amount of liquid. Therefore, if a solute adsorbs preferentially at the interface, the concentration of the solute in the foam will be greater than in the solution from which the foam has been generated. This effect provides a simple method of concentrating materials which have a tendency to adsorb on the gas-liquid interface. This is particularly relevant to biomaterials like whole cells, proteins, enzymes etc., which are surface active and are present in low concentrations in the broth. Foam separation has therefore attracted considerable attention, and several reports exist in literature on concentrating cells, proteins and enzymes using foams. Foam separation is based on the difference in surface activity of the components to be separated. A surface active molecule consists of a lyophobic and a lyophilic group. (As water is commonly used as a solvent, the lyophilic and lyophobic groups are called hydrophilic and hydrophobic groups, respectively). When dissolved in a solvent, the presence of lyophobic groups in the interior of the solvent distorts the solvent liquid structure, thereby increasing the free energy of the system.

Foam separation is a simple and economic method for separation of surface-active molecules such as proteins and enzymes from aqueous solutions. In this study, lactic acid broth, spent brewer&rsquo / s yeast extract and residual beer was used to investigate the applicability and efficiency of foam separation technique in partial purification of fermentation products and recovery of valuable components from industrial waste streams. The effects of the process variables initial feed concentration, air flow rate, foaming time, liquid pool height and temperature on separation performance were studied and optimum conditions for removal of proteins from lactic acid broth was determined. Highest enrichment (172.2) and separation ratio (314) with a high protein recovery (45.2 %) were obtained by foaming 200 ml of lactic acid broth with an initial feed concentration of 0.018 mg/ml at an air flow rate of 38.5 cm3/min. Selectivity of foam separation in protein purification, and its effect on protein structure was investigated in brewery wastes using SDS-PAGE and native PAGE, respectively.

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