Calcium pectate gel beads for cell entrapment. 6. Morphology of stabilizedand hardened calcium pectate gel beads with cells for immobilized biotechnology

The structure of standard and stabilized calcium pectate gel (CPG) beads ha s been examined by scanning (SEM) and transmission (TEM) electron microscop y. A two-stage crosslinking procedure with polyethyleneimine (PEI) and glut araldehyde (GA) led to the formation of a more compact layer on the bead su rface. On the other hand, the stabilization procedure did not significantly change either gel bead interior or morphologic properties, vitality and bi otransformation activity of immobilized bacterial cells (Nocardia tartarica ns) against cis-epoxysuccinate as well as yeast cells (Trigonopsis variabil is) against cephalosporin C. The structure of these cells within the calciu m pectate matrix remained unchanged. Moreover, the two-step chemical stabil ization of CPG containing T. variabilis or N. tartaricans had a favourable effect on storage and operational stability at semi-continuous and continuo us processing in stirred batch and packed-bed reactors. The most valuable e ffect of stabilization was the fact that the hardened CPG comprising the ce lls N. tartaricans resisted, for a long time (360 days and more), the destr uctive effects of the product (such strong sequestering reagent as L-(+)-ta rtaric acid) at high concentrations (up to 1 M). Non-hardened CPG was destr oyed after 21 h. The reference materials, hardened and non-hardened calcium alginate gels (CAG), were destroyed over 3h or 30 min, respectively.