INFLUENCE OF WATER ACTIVITY ON THE SYNTHESIS OF TRIOLEIN CATALYZED BYIMMOBILIZED MUCOR-MIEHEI LIPASE

The influence of the thermodynamic activity of water (a(w)) on the syn thesis of triolein catalyzed by Mucor miehei lipase was investigated. Its effect on the equilibrium and on the rates of the different reacti ons present, esterification and mono- and diglyceride isomerization, w as evaluated through measurements made in controlled water activity at mosphere. The apparent equilibrium constants were measured from the co ncentration of the different species as a function of the initial glyc erol-to-oleic-acid ratio using all the values at once with a multiresp onse nonlinear regression technique. Rate constants were determined fr om kinetic measurements and nonlinear regression using the variation o f the concentration of all significant species in the system. Except f or the synthesis of diolein from monoolein, which shows a maximum for a(w) approximate to 0.5, the apparent rate constants of the various re actions are not significantly affected by the value of the water activ ity. The equilibrium is shifted toward the synthesis of triolein for l ow values of a(w), indicating that in the design of a process for trig lyceride synthesis, using M. miehei lipase as a catalyst, the water ac tivity can be lowered to extreme values to favor the synthesis, withou t any sacrifice on the productivity of the process. (C) 1995 John Wile y & Sons, Inc.