Optimization of media composition for improving conversion of isoeugenol into vanillin with Pseudomonas sp. strain KOB10 using the Taguchi method

The popular demand for natural food additives has resulted in a number of processes for producing natural vanillin. Although there are chemical procedures and plant sources for vanillin production, microbial bioconversions are being sought as a suitable 'natural' alternative. The present paper describes the conversion of isoeugenol to vanillin by a novel bacterial strain isolated from soil. The strain was identified as Pseudomonas sp. strain KOB10 based on morphological and physiochemical characteristics and its 16S rDNA gene sequence. We optimized medium composition for vanillin production using a Taguchi experimental design. Eight factors, i.e. isoeugenol, glycerol, tryptone, K2HPO4, KH2PO4, Cu2+, Mg2+ and Ca2+ concentrations, were selected and experiments based on an orthogonal array layout of L 18 (2(2) x 3(6)) were performed. Analysis of the experimental data using the Taguchi method indicated that Cu2+ and glycerol concentrations had the highest impact on isoeugenol conversion into vanillin at a substrate concentration of 0.9 g L-1. Under the optimized conditions, growing cells of Pseudomonas sp. strain KOB10 produced 0.153 g vanillin L-1 from 0.9 g isoeugenol L-1, with a molar yield of 18.3% after incubation for 48 h. To improve the vanillin yield, the effect of other bioconversion parameters including time of isoeugenol addition, initial isoeugenol concentration and conversion time was studied; the results showed a maximum concentration of 3.14 g vanillin L-1 after a total incubation time of 88 h with 15 g isoeugenol L-1, which corresponded to a molar yield of 22.5%. Further standardization and optimization for vanillin production was challenging.