Factors influencing the stability of a novel enzyme immobilisation support - colloidal liquid aphrons (CLAs)

Abstract

A key factor in the immobilisation of enzymes is the stability of the support. An investigation was carried out on the stability of colloidal liquid aphrons (CLAs) in dilute dispersion, looking particularly at the effects of process parameters and CLA composition. CLAs were formulated from a Softanol 30/decane solvent phase and sodium dodecyl sulfate (SDS)/β-galactosidase aqueous phase. The aim of this work was to gain an understanding of the mechanisms stabilising CLAs, and to characterise the effects of process parameters on stability such that the knowledge gained could be used in the design of a membrane bioreactor. CLA stability was measured using a light scattering technique (defined by a first order CLA half-life). It was proposed that CLA break-up occurred by the collision of CLAs with sufficient energy to overcome the forces stabilising the CLAs. Stability was found not to be dependent on the bulk aqueous phase ionic strength, but increasing the concentration of the ionic surfactant increased stability, indicating that stability was influenced by charge repulsion. Stability was also found to increase for increasing enzyme (β-galactosidase) concentration, indicating steric interactions and elastic effects were also important. Finally, the effect of process parameters (reactor temperature, CLA concentration and circulation velocity) were assessed, and their effect was explained in terms of their influence on collision energy and the activation energy necessary for CLA break-up; increasing CLA concentration was found to improve stability considerably. © 2000 Society of Chemical Industry