Hydrolysis of Butteroil by Immobilized Lipase Using a Hollow-Fiber Reactor: Part V. Effects ofph.

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Abstract
A lipase from Aspergillus niger, immobilized by adsorption on microporous, polypropylene hollow fibers, was used to effect the hydrolysis of the glycerides of melted butterfat at 40°C and pH values of 3.0, 4.0, 5.0, 7.0, 8.0, and 9.0. The aqueous phase and the melted butterfat were pumped in a cocurrent fashion through the lumen and the shell sides, respectively, of a hollow fiber reactor. Nonlinear regression methods were employed to independently fit the data set obtained at each pH to models based on combinations of three nested rate expressions for the hydrolysis and three nested rate expressions for thermal deactivation of the enzyme. A rate expression containing 4 lumped parameters is sufficient to model the release of free fatty acids at each of the six pH values as a function of reactor space time and time elapsed after immobilization. Nonlinear regression methods were also employed in global fits of the data to rate expressions containing an explicit dependence on pH. For the reaction conditions used in this research, a 14-parameter rate expression is necessary to accurately model the overall release of free fatty acids as a continuous function of pH, initial substrate concentration, reactor space time, and time elapsed after immobilization of the lipase.