Calcium pectate gel beads for cell entrapment. 4. Properties of stabilized and hardened calcium pectate gel beads with and without cells
1992
Kurillova, L. | Gemeiner, P. | Ilavsky, M. | Stefuca, V. | Polakovic, M. | Welwardova, A. | Toth, D.
Potassium pectate prepared by enzymatic de-esterification of apple pectin forms, after crosslinking with calcium ions, a gel with many properties useful for cell entrapment. However, calcium pectate gel (CPG) beads should be stabilized and hardened when used continuously. Thus, preformed beads were treated with polyethyleneimine (PEI) followed by glutaraldehyde (GA). In this way, a stabilized layer which substantially increased the stability of the CPG beads against Ca2+-complexing reagents (phosphate, citrate), pH, and mechanical stress was formed. Stabilization and hardening of the CPG beads did not substantially change the morphologic properties of the beads such as the porosity, pore size distribution, size-exclusion limit, effective diffusion coefficient, or original plasticity. Entrapped cells reduced the network density of CPG beads determined from mechanical measurements and negatively affected the resistance of CPG material to deformation, even when stabilized with PEI and GA. For viability and toxicity testing, only the short-term exposure of GA was chosen. The effect of GA on the stability of CPG beads was perceptible: during the continuous operation of untreated CPG beads with entrapped Saccharomyces cerevisiae in a packed-bed reactor at 60 degrees C and 2 M sucrose the physical and biocatalytic properties were impaired whereas the stabilized and hardened CPG beads with entrapped cells were sufficiently stable under the same conditions. After storage at 4 degrees C with repeated intermittent operation at 30 degrees C in phosphate buffer for 1 month, entrapped Trigonopsis variabilis maintained even 98% of their transformation (D-amino acid oxidase) activity against cephalosporin C.
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