Bioconversion of limonene to α-terpineol by immobilized Penicillium digitatum

Abstract

Bioconversion of (4R)-(+)-limonene to (4R)-(+)-α-terpineol by immobilized fungal mycelia of Penicillium digitatum was investigated in batch, repeated-batch and continuously fed systems. The fungi were immobilized in calcium alginate beads. These beads remained active for at least 14 days when they were stored at 4 °C. Three different aeration rates were tested. The highest yield was obtained at a dissolved oxygen level of 50.0 μmol/l. α-Terpineol production by this fungus was 12.83 mg (g beads)⁻¹ day⁻¹, producing a 45.81% bioconversion of substrate. Repeated-batch bioconversion showed yield decreases in the second and the third cycles. Regeneration with nutrient media after the third cycle improved the bioconversion yields. With continuous bioconversion, the half-life was dependent on the aeration. The optimum conditions with a continuous reactor were at an aeration rate of 0.3 standard l/min and a dilution rate of 0.0144 h⁻¹.