Vanillin ferulic acid degradation

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]. 

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. 

Bonnin, E. et al., Aspergillus niger 1-1472 and Pycnoporus cinnabarinus MUCEL 39533, selected for the biotransformation of ferulic acid to vanillin, are also able to produce cell wall polysaccharide-degrading enzymes and feruloyl esterases, Enzyme Microb. Technol, 28, 70, 2001. 

Later, Tressl et al. (1976) also proceeded to the thermic degradation (2 h, 200 JC) of ferulic acid (H.87) and identified the same phenols as Fiddler et al., plus 4-isopropylguaiacol and vanillin alcohol (4-hydroxy-3-methoxybenzenemethanol) which have not been found in coffee. For isoeugenol (H.38), the formula is written as the (E)-( trans -) isomer, but nothing was specified in the text. Tressl et al. (1976) also published the results of thermal decomposition of cinnamic, p-coumaric (H.84) and sinapic (H.90) acids. Many of the simple phenols (and other aromatic compounds) formed have also been identified in roasted coffee volatiles. A thermic fragmentation of quinic acid (E.62) has shown that simple acids, phenols and polyphenols originate from this precursor (Tressl et al., 1978a). 

Fig. 3.8 A scheme showing the formation of ferulic acid and vanillin by a sequence of hydrogen abstraction and OH" addition reactions between curcumin or its degradation products and eight OH [149]...

Fig. 3.8, TSs and TS s symbolically represent sets of three and four transition states respectively. The structures shown near TSs and TS s are those of the last transition states in each set. RC and PC stand for reactant complex and product complex respectively. M stands for the molecule lying near ferulic acid in Fig. 3.8. In the RC of Fig. 3.8, an OH radical is already added at the CIO site. A sequence of addition and hydrogen abstraction reactions (Fig. 3.8) lead to the formation of fera-lic acid and vanillin. Thus curcumin and its degradation products in total scavenge eight OH radicals.

Fig. 5.26. Thermal degradation of ferulic acid. 4-Vinyl-guaiacol (I), vanillin (II), and guaiacol (III) (according to Tressl et al., 1976)...

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. 

Detoxification procedures are often required for acidic and steam-exploded lignocellulosic hydrolysates, as variable concentrations of toxic furans (furfural and 5-HMF), lignin degradation compounds (aromatics and phenolics including vanillin, catechol, guaiacol, ferulic acid, syringaldehyde, and 4-hydroxy-... 

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