Invertase activity of Saccharomyces cerevisiae cells entrapped in poly-2-hydroxy-ethylmethacrylate gels: kinetic and thermostability study in membrane reactors

Films of poly (2-hydroxyethyl methacrylate) with entrapped yeast cells have been prepared and characterized in membrane reactors. Two concentrations, 5 and 10% w/w, of crosslinking agent ethylene dimethacrylate are used. The invertase activity is monitored between 30 and 55-degrees-C in the range of sucrose concentration from 40 to 200 mM and during almost 600 h of operation. Comparison is also made with the behaviour of free cells and small size particles (less than 115 mesh) of poly-HEMA immobilized cells. The results show that the whole membrane volume is not involved in substrate permeation and a combined diffusion-reaction rate controlling mechanism holds. An unusual dependence of reaction rate on bulk pH is observed. In the range of pH from 4.0 to 6.0, invertase activity in films continuously increases while two distinctive maxima for free yeast cells (pH 4.75) and for small particles of poly-HEMA-immobilized yeast cells (pH 4.5) are observed.