USE OF A LIPASE IMMOBILIZED IN A MEMBRANE REACTOR TO HYDROLYZE THE GLYCERIDES OF BUTTEROIL

A lipase from Aspergillus niger, immobilized by adsorption on a microporous, polypropylene flat-sheet membrane, was used to effect the continuous hydrolysis of the glycerides of melted butterfat at 35-degrees-C. For the reaction conditions used in this research, a pseudo-zero order rate expression can be used to model the kinetics of the overall hydrolysis of butterfat. Multiresponse nonlinear regression methods were employed to determine the kinetic parameters of a multisubstrate rate expression derived from a mechanism based on the general Michaelis-Menten approach. For the multiresponse data taken at pH 7.0, the dependence of the maximum rate of release of each fatty acid residue of butterfat on its carbon chain length is accurately described by a skewed, bell-shaped (or GAMMA-type) distribution. Data taken at five different pH values were fit assuming a Dixon-Webb diprotic model for the pH dependence of the reaction rate. The thermal deactivation of the immobilized lipase obeyed first-order kinetics with a half-life of 19.9 days at 35-degrees-C. The multisubstrate model is useful for the prediction of the free fatty acid profile of lipolyzed butterfat, whereas the lumped-substrate model provides an estimate of the overall degree of hydrolysis as a function of the reactor space time.