Heterologous glucoamylase production with immobilised Kluyveromyces lactis cells in a fluidised bed reactor operating as a two-(liquid-solid) or a three-(gas-liquid-solid) phases system Process Biochemistry

Viable cells of Kluyveromyces lactis, transformed with the glucoamylase gene from Arxula adeninivorans, were entrapped in beads of Ca-alginate and employed on a lab scale in a fluidized bed reactor, operating as a two-phase (liquid-solid) or a three-phase (gas-liquid-solid) system, to produce glucoamylase. The reactor was fed with a non-selective medium containing lactose as carbon source and filled with controlled-sized beads having a 2.11 mm diameter. The performance of the three-phase system, in terms of specific glucoamylase productivity, resulted higher than that of the two-phase operating one. Further, higher product concentrations in the outlet were achieved, due to the possibility to enhance the substrate average residence time. In both systems, the performance of the immobilised cells was strongly affected by mass transfer limitations occurring throughout the gel.