Phase transfer and biocatalyst behaviour during biotransformation of β-ionone in a two-phase liquid system by immobilised Aspergillus niger

Abstract

The biotransformation of β-ionone by Aspergillus niger IFO 8541 entrapped in Ca-alginate beads was investigated in a two-phase liquid system, due to the low aqueous solubility of the precursor. Modelling of phase transfer processes of the substrate demonstrated that the solute was transferred from the organic droplets to the gas, giving a loss by stripping, and then from the gas to the aqueous solution where a chemical degradation occurred. The biological reaction took place after direct precursor transfer from the organic layer to the biocatalyst by surface adsorption. Studies on the biological process demonstrated the critical effect of the biomass content in the medium at the time at which β-ionone was added. Optimum conditions involved fed-batch feedings of both precursor and carbon source (sucrose) after the biomass concentration reached a value close to 6.8 g/l. The biotransformation process then took place at a constant rate of 0.046 mmol/l h with a reaction yield, defined with respect to β-ionone metabolised by the fungus, close to unity. Best results achieved in this study allowed to obtain 3.5 g/l biological compounds after 400 h reaction.