Abstract
BACKGROUND: Although advantages of immobilization of cells through entrapment in calcium alginate gel beads have already been demonstrated, nevertheless, instability of the beads and the mass transfer limitations remain as the major challenges. OBJECTIVE: The objective of the present study was to increase the stability, porosity (reduce mass transfer limitation), and cell immobilization capacity of calcium alginate gel beads. MATERIALS AND METHODS: Sodium alginate was mixed with various concentrations of the starch or sugar and gelled in 2% calcium chloride solution. During the gelling and curing, the starch or sugar leached out of the beads and created micro-pores. RESULTS: Micro-porous beads prepared with starch were more stable and had higher immobilization capacity than those prepared with sugar. After 24 hours of incubation (curing) of the micro-porous beads prepared with starch in calcium alginate, the solubilization time in citrate buffer was 93 minutes compared to 41 minutes for the control beads (without starch). The compressive strength of the micro-porous beads was also higher (5.62 Mpa) than that of the control beads (5.54 Mpa). The optimal starch concentration for cell immobilization was 0.4%. With this starch concentration, the immobilized Bacillus subtilis and Saccharomyces cerevisiae cell densities were 5.6 × 10(9) and 1.2 × 10(8) cells/beads, respectively. These values were 36.5% and 74% higher than the value obtained for the control beads. This method of immobilization resulted in more uniform cell distribution. CONCLUSION: Addition of starch to the sodium alginate solution before gelation in calcium chloride solution increased the stability of the beads, increased the immobilized cell density, and resulted in a more uniform cell distribution in the beads.