Vanillin formation from ferulic acid

Figure 2 PVG and vanillin formation from ferulic acid following its release...

In 1965, Zenk, using radioactively labelled ferulic and vanillic acids, proposed a route by which both vanillin and vanillic acid were derived from ferulic acid. A CoA-dependent /3-oxidative cleavage of feruloyl-CoA led to the formation of vanilloyl-CoA,... 

The bioconversion of eugenol and ferulic acid to vanillin was first characterised in Pseudomonas fluorescens (Scheme 26.4) [36, 37]. However, an enzyme of the pathway, vanillin NAD+ oxidoreductase, catalysed the removal of vanillin from the medium through the formation of vanillic acid [38]. Deletion of the oxidoreductase was, however, only partially successful, largely because vanillin is also the substrate of coniferyl aldehyde dehydrogenase, an enzyme of the eugenol degradative pathway present in Pseudomonas sp. [39]. 

A new model (Fig. 15.4) for hydroxy-cinnamate chain-shortening and vanillin formation in plants was revealed with the isolation of 4-hydroxycinnamoyl-CoA hydratase/lyase (HCHL) and its gene from a soil bacterium, Pseudomonas fluorescens strain AN103, which had been isolated by growth on ferulic acid as a sole carbon source (Gasson et al., 1998 Narbad and Gasson, 1998 Mitra et al., 1999). 

Phenolic aroma compounds can be generated by the thermal radical degradation of phenolic acids such as ferulic acid (52), which is a constituent of many vegetable raw materials [76]. Fig. 3.32 shows the formation scheme for vinylguaiacol (53), vanilline (54) and guaiacol (55) from 52. 

Ferulic acid is the major cinnamic acid found in a variety of plant cell walls. Com fiber contains about 3% femlic acid. Wheat bran is another source of ferulic acid (0.5-1%). Faulds et al. 226) developed a laboratory scale procedure to produce free femlic acid (5.7 g) from wheat bran (1 kg) by using a Trichoderma xylanase preparation and A, niger femlic acid esterase. Using filamentous fungi, a two-stage process for vanillin formation was developed in which a strain of A. niger was first used to convert femlic acid to vanillic acid, which was then reduced to vanillin by a laccase-deficient strain of Pycnoporus cinnabarinus 227). 

Orange juice from rediluted concentrate differs in its aroma. This can be the result of big losses of acetaldehyde and (Z)-3-hexenal, the formation of carvone by peroxidation of limonene and a large increase in the vanillin concentration, probably due to the degradation of ferulic acid. 

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