Optimization of the hardening treatment of S. cerevisiae bioparticles

Immobilization of microorganisms for application in fermentation processes generates bioparticles whose mechanical properties can be greatly improved if they are subjected to a hardening process. In this work, the immobilization of Saccharomyces cerevisiae in κ-carrageenan and their treatment with Al(NO₃)₃ as hardening agent have been optimized. The effect of several factors have been studied, including the cell concentration in the gel, the concentration of hardener, and time of contact of this latter with bioparticles. In repeated batch experiments, a factorial design technique has been employed, reaching high values of productivity and a good retention of particles in the matrix. Once optimal conditions were selected, continuous experiments were realized, in which the hardened beads showed significant advantages, such as increase of 20% in ethanol productivity, a better evacuation of gas from the reactor, and a higher cell retention.