A multi point conductivity measurement system for characterisation of protein foams

Abstract

Protein foams play an important role in both food and biotechnological processes. A sound understanding of foaming properties of proteins relevant to such processes is useful e.g. to allow adequate control of unwanted foams and appropriate choice of protein-physical system when foams of certain characteristics are required. In general, measurements of changes in foam volume (volumetric method) are used for foam characterisation. However, recently there has been increased interest in the use of measurement methods based on conductivity and capacitance. Simple relative techniques based on electrical conductivity measurements provide information on both foamability and foam stability. A multi point conductivity measurement system has been designed and used for characterisation of model protein foams (0.1 and 1.0 mg ml −1 Bovine serum albumin, BSA). The solution of BSA was sparged with nitrogen or carbon dioxide gas at constant flow rate (90 cm 3 min −1) via a stainless steel sinter (0.5 or 2.0 μm in pore size). A comparison of foaming properties determined by volumetric and conductimetric techniques is provided. Both methods show that more stable foams are obtained for solutions at higher BSA concentrations. At all BSA concentrations, higher foamability and stability are achieved with a smaller sinter pore size. When nitrogen rather than carbon dioxide is used as a dispersed phase, higher foamability and foam stability are obtained. The conductivity measurements indicate that foamability is dependent on gas type, whereas, volumetric measurements do not show such differences.