HYDROLYSIS OF BUTTEROIL BY IMMOBILIZED LIPASE USING A HOLLOW-FIBER REACTOR .6. MULTIRESPONSE ANALYSES OF TEMPERATURE AND PH EFFECTS

A lipase from Aspergillus niger, immobilized by physical adsorption on hydrophobic hollow fibers made of microporous polypropylene, was used to effect the hydrolysis of the glycerides of melted butterfat at 40, 50, 55, and 60-degrees-C (pH 7.0), and at pH 3.0, 4.0, 5.0, 7.0, 8.0, and 9.0 (40-degrees-C). McIlvane buffer and melted butterfat were pum ped cocurrently through the hollow fiber reactor. The concentrations o f ten different free fatty acids in the effluent oil stream were measu red by HPLC. Multiresponse nonlinear regression methods were employed to fit the data to multisubstrate rate expressions derived from a Ping Pong Bi Bi mechanism in which the rate controlling step is deacylatio n of the enzyme. Thermal deactivation of the immobilized lipase was al so included in the mathematical model of reactor performance. A postul ated normal distribution of v(max) with respect to the number of carbo n atoms of the fatty acid residue (with an additive correction for the number of double bonds) was found to provide the best statistical fit of the data. The models developed can be used to independently predic t the effects of either the pH or the temperature, as well as the reac tor space time and the time elapsed after immobilization, on the free fatty acid profile of the lipolyzed butteroil product.