Recovery of vanillin obtained via microbial bioconversion using membrane contactors

Vanillin (4-hydroxy-3-methoxybenzaldehyde), the major component of natural vanilla, is widely used in food, beverage, cosmetic and pharmaceutical industries. Since natural vanillin, extracted from the pods of the tropical vanilla orchid, features both high price and limited supply, chemically synthesized vanillin occupies more than 99% of the market share. The increasing concern for health and nutrition stimulates a worldwide demand for “natural” vanillin. Our studies have been focused on vanillin production from ferulic acid by using a Pseudomonas sp. strain and from capsaicin via an enzymatic process. In both microbial and enzymatic transformations the productivity can be potentially enhanced by in-situ removal of vanillin, avoiding the product inhibition and further transformation of vanillin to side products. The goal of this research is to evaluate the potential of using membrane based solvent extraction for the recovery of vanillin in view of the on-line extraction from the bioconversion broth, thus coupling bioconversion and separation. Various solvents were tested measuring the partition coefficients for vanillin and other relevant compounds. Good properties were shown by ethyl and n-butyl acetate, which allow the selective removal of the produced vanillin from the bioconversion broth removing only a minor extend of the substrates. The partition coefficient of vanillin depends on pH: at higher pH values vanillin becomes more soluble in water than in the solvent. This behaviour suggests the possibility to counter-extract vanillin from the vanillin rich solvent phase by using alkaline water, from which pure vanillin can be eventually obtained by crystallization. Extraction and counter-extraction experiments were performed by hollow fibre modules; the feed flowed either through the lumen or in the shell side. The kinetics of mass transfer was investigated in batch experiments. The overall mass transfer coefficients were calculated from the data and compared with theoretical values.