microbial bioconversion

The rising popularity of natural aroma products such as vanillin and vanillic acid has triggered off significant research activities to use biocatalysts for the production of natural flavor compounds. We conducted this study to screen moderately halophilc bacteria which are able to degrade ferulic acid and to study the possibility of forming vanillic acid via conversion of ferulic acid under resting cells conditions. 22 different strains of bacteria were isolated from different samples collected from the salty environments of Iran. Primary screening was performed by HPLC analyse. The selected strains were identified based on physiochemical characteristics as well as molecular phylogenetic analysis. Biotransformation mixtures were quantified for vanillic acid content and the other produced methoxyphenols by HPLC analyse. Based on the HPLC results obtained، among the 22 isolated strains، resting cells of Halomonas salina HSL5 (GenBank accession number JQ327041) produce the greatest quantity of vanillic acid (397 mg/l، molar yield of 46. 8%) after a 24-h reaction time، without further optimization The current study brings the first report for bioconversion of ferulic acid to vanilic acid in the Halomonas salina.

In the recent years, the use of microbial biotransformation processes to achieve specific properties of vanillin and access to the natural vanillin origin has been a lot of attention. In the present study, Taguchi method was employed for optimizing the biotransformation of isoeugenol to vanillin under resting cells of native isolate Psychrobacter sp. strain CSW4. Five factors, i.e. initial isoeugenol concentration, initial dry biomass, co-substrates (glycerol, yeast extract and tryptone), initial NaCl concentration and metal ions (Cu, Zn and Co, were selected and experiments based on an orthogonal array layout of L18 were performed. Vanillin produced in the biotransformation reaction mixture was analyzed by HPLC method. Optimization of the process by Taguchi method showed that highest impact factors with importance priority of NaCl concentration, initial isoeugenol concentration, glycerol as substrate, cobalt ion and initial dry biomass were determined as optimum conditions for the biotransformation isoeugenol into vanillin, respectively. Under these optimized conditions, the highest vanillin concentration (1.016 g/L) obtained after 24-h reaction biotransformation. The molar yield of vanillin produced from isoeugenol was 43.8%. Results of this study indicate that if optimization of medium composition is performed to balance the cell growth and vanillin amount, reasonable yields of vanillin have been achieved, without addition ofany toxic organic solvent or other chemicals which increase the cost of production.