Effects of preparation variables of enzyme-encapsulating water-in-oil emulsion on enzymatic reaction conversion and emulsion stability in an enzyme–emulsion–liquid–membrane reactor

Abstract

The effects of various water-in-oil (W/O) emulsion preparation variables, such as water-to-oil volume ratio of W/O emulsion, emulsification speed and time, and emulsifying agent concentration, on the permeation rates of l-phenylalanine methyl ester ( l-PME, substrate) and l-phenylalanine ( l-Phe, product) were investigated in an enzyme–emulsion–liquid–membrane (EELM) system accompanying the hydrolysis of the substrate into the product. The permeation rate of the substrate was higher in the system with a higher water-to-oil volume ratio or lower emulsification energy, while emulsifying agent concentration had little influence on its permeation rate as far as emulsion was stable. The permeation rate of the product was highest in the system with water-to-oil ratio of 1/1, the lowest emulsification energy or 7 wt.% emulsifying agent concentration. This is because the rate was dependent only on the mass transfer resistance, such as surfactant layer resistance at interfaces, membrane thickness, and the mass transfer area between external phase and emulsion drops. The explanation was supported by the experimentally measured data of emulsion drop size, emulsion viscosity, and internal droplet size. Finally, the optimum permeation rate was obtained at 7 wt.% emulsifying agent concentration, water-to-oil volume ratio of 1/1 and emulsification speed of 6000 rpm for 15 min.