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

A key factor in the immobilisation of enzymes is the stability of the suppo rt. An investigation was carried out on the stability of colloidal liquid a phrons (CLAs) in dilute dispersion, looking particularly at the effects of process parameters and CLA composition. CLAs were formulated from a Softano l 30/decane solvent phase and sodium dodecyl sulfate (SDS)/beta-galactosida se aqueous phase. The aim of this work was to gain an understanding of the mechanisms stabilising CLAs, and to characterise the effects of process par ameters on stability such that the knowledge gained could be used in the de sign of a membrane bioreactor. CLA stability was measured using a Light sca ttering 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 con centration of the ionic surfactant increased stability, indicating that sta bility was influenced by charge repulsion. Stability was also found to incr ease for increasing enzyme (beta-galactosidase) concentration, indicating s teric interactions and elastic effects were also important. Finally, the ef fect of process parameters (reactor temperature, CLA concentration and circ ulation velocity) were assessed, and their effect was explained in terms of their influence on collision energy and the activation energy necessary fo r CLA break-up; increasing CLA concentration was found to improve stability considerably. (C) 2000 Society of Chemical Industry.