Fungal Bioconversion of Agricultural By-Products to Vanillin

The ester-linked ferulic acid of wheat bran and sugar-beet pulp can be converted to vanillin using biological transformation. Free ferulic acid from sugar-beet pulp and from wheat bran was almost quantitatively obtained by extensive degradation of the cell-walls using enzyme mixtures complemented with specific ferulic acid esterases. TheBasidiomycete Pycnoporus cinnabarinusthen converted the released ferulic acid to vanillin. The selection of stable and highly productive strains was achieved using formal genetics. The use of cellobiose as an activator of the vanillin pathway, and the sequential addition of a precursor (ferulic acid) in cultures of selectedP. cinnabarinusstrains, allowed 90 and 300 mg/L of vanillin to be obtained from ferulic acid enzymically released from wheat bran and sugar-beet pulp, respectively. This process was adapted into a two-step process involving two filamentous fungi,Aspergillus nigerandP. cinnabarinus, with complementary capabilities of transformation.