Vanillin production from ferulic acid obtained from wheat bran.

Several studies have been recently focused on the production of specialty chemicals such as flavour compounds from wastes or surplus of the agro-industry as a possible way of both disposing and valorising them. Cereal bran, one of the most widely produced agricultural processing by-product, can be of interest in vanillin production as it is a potential source of ferulic acid, from which vanillin can be obtained via microbial bioconversion. Ferulic acid is linked to cell wall polysaccharides through ester links, which have to be hydrolyzed to release ferulic acid. The aim of this work was to produce vanillin from wheat bran through: a) enzymatic hydrolysis of wheat bran and b) bioconversion of the resulting ferulic acid into vanillin by employing a recombinant E. coli strain containing the genes for the bioconversion of ferulic acid to vanillin (E. coli JM109/pBB1). Wheat bran was hydrolyzed with a mixture of two commercially available enzymes, thus obtaining 1323 mg of ferulic acid/kg of dried wheat bran. The bran hydrolyzate also contained a high carbohydrate concentration. Bioconversion of ferulic acid present in the extract was assayed by using resting cells of E. coli JM109/pBB1, thus obtaining a vanillin molar yield of 50% from an initial ferulic acid concentration of 0.75 mM. However, this yield was significantly lower than that obtained with pure ferulic acid at the same initial concentration. Therefore, ferulic acid was recovered from the crude bran extracts by employing ion exchange resins with the concomitant removal of carbohydrates. In these conditions, vanillin molar yield was increased up to 70%. The results obtained pointed out that vanillin can be obtained at interesting yields from wheat bran, an agriculture by-product produced in large amounts in Italy.