Ferulic acid transformation

There is a substantial literature on the transformation of simple phenolic acids by microorganisms.2,7,11,16,18,20,22,25,29,44 For example, ferulic acid is transformed by fungi to either caffeic acid or vanillic acid, and these are transformed to protocatechuic acid. Next the ring structure of protocatechuic acid is broken to produce 3-carboxy-c/s,c/s-muconic acid, which is then converted to (3-oxoadipic acid (Fig. 3.1), which in turn is broken down to acetic acid and succinic acid, and these ultimately are broken down to C02 and water.11,18,29 Flowever, distribution of residual 14C-activity after growth of Hendersonula toruloidea, a fungus, in the presence of specifically 14C-labeled ferulic acid ranged from 32 to 45% in C02, 34 to 45% in cells, 9 to 20% in humic acid and 4 to 10% in fulvic acid.29 Thus, a considerable portion of the ferulic-acid carbon was bound/fixed over a 12-week period, and the initial ferulic acid transformation products (e.g., caffeic acid, vanillic acid and protocatechuic acid) were clearly of a transitory nature. Similar observations have also been made for other simple phenolic acids 22,23 however, the proportions metabolized to C02 and fixed into cells and the soil... 

Ferulic acid is the most abundant hydroxycinnamic acid in cereal grains. The content in wheat grain is approximately 800-2000 mg/100 g DW. It is found chiefly in the outer part of the grain, in the trans form, which is transformed into arabinoxylans and... 

Grbic-Galic, D. (1986). Anaerobic production and transformation of aromatic hydrocarbons and substituted phenols by ferulic acid-degrading BESA-inhibited methanogenic consortia. FEMS Microbiology Ecology, 38, 161-9. 

In order to eluddate the mechanism of the further transformations of the primary lignin decomposition products including the cleavage reactions, we synthesized some of the important primary products labelled with Cu and introduced these into the cultures of fungi or enzymes. Thus, it could be shown, for example, that the breakdown of the side chain of ferulic acid occurs at the double bond vanillic acid is found. During polymerization in the presence of phenoloxidases, in the case of carboxyl-labelled ferulic acid, about 60% of the activity is split off as Cli02. The polymers labelled in the 2 and 3 position in the side chain or in the methoxyl group contain the whole applied activity. 

Phenolic compounds in plants play a role in disease resistance (Morandi, 1996). Mycorrhizal plants of maize accumulated more phenolic compounds p-hydrocinnamic acid and ferulic acid in roots than non-mycorrhizal plants (Huang, 2003). Mycorrhizal Ri T-DNA transformed carrot roots accumulated more phenolic compounds when challenged by Fusarium oxysporum (Benhamou et al., 1994). All cultivars of pea colonized with G. mosseae accumulated more phenolic acids, and total phenolic accumulation were closely correlated to disease intensity (Singh et al., 2004). 

Synthesis of caffeic and ferulic acids also needs hydroxylase and methyltransferase enzymes transformation into hydroxycinnamic tartaric acid esters (HCTA) is operated by an acyltransferase enzyme. The scheme shown in Figure 2.9 summarizes the biosynthetic pathways described. 

Figure 3 Expression of a ferulic acid esterase from N. crassa in E. coli. Cells were grown at 38°C and induced at ODb00 — 0.4 with 0.4 mM IPTG. C control strain transformed with pET3a. P protein expression strain transformed with pET3afizs-. Pperi periplasmic fraction. Pcyto cytoplasmic fraction. Pmemb membrane and inclusion bodies fraction. M standard protein molecular weight. — pre-induction. + post-induction...

Five transformants produced a major secreted protein band, with an estimated molecular weight of 40 kDa and no protein was detected in the control. The estimated molecular weight is greater than that predicted or observed from E. coli, which is likely due to post-translational modification. P6 and P10 transformants were retained to perform enzymatic assays. The culture supernatants were assays for activity against methyl caffeate (MCA) and methyl ferulate (MFA). The recombinant proteins were shown to be active as a feruloyl esterase and show the characteristics of a type B ferulic acid esterase.6 Feruloyl esterase activity is reported in Table 1. 

Further studies about the biosynthesis of SA have been carried out in rice (Oryza sativa). In agreement with the SA biosynthetic pathway in tobacco, SA is synthesized from CA via BA. In addition to the conversion of [ C]-CA into SA, it is also transformed to the lignin precursors /7-coumaric acid and ferulic acid. [" C]-benzoic acid was readily converted to SA [32]. 

Some phenolic acids like caffeic acid, p-coumaric acid and ferulic acid can act as precursors of volatile phenols, which could contribute positively to wine aroma, when they are present at low concentrations associated descriptors are smoky, dove-like and leather (Table 1). Yeasts can conduct the decarboxylation of phenolic adds to volatile phenols, as well as esterase activities present in enzymatic preparations used in winemaking. During wine storage and ageing, volatile phenols may be further transformed. 

Other strains, like VLl, were selected for their low vinyl-phenol production. These compounds possess rather unpleasant pharmaceutical aromas. Above a certain concentration, they dull the aroma of dry white wines (Volume 2, Sections 8.4.2 and 8.4.3). These strains have low cinnamate decarboxylase activity. During alcoholic fermentation, this enzyme catalyzes the partial transformation of p-coumaric and ferulic acid found in juice into vinyl-4-phenol and vinyl-4-gaiacol. Since this enzyme is inhibited by phenolic compounds, only white wines can contain quantities of vinyl-phenols likely to affect their aroma. The use of strains with low cinnamate decarboxylase activity is recommended— particularly for white juices containing high concentrations of hydroxy cinnamic acid. 

Also, a two-step process was patented in 1996 [49], employing two different filamentous fungi Aspergillus niger and Pycnoporus cinnabarinus. In the first step, A. niger transformed ferulic acid to vanillic acid, and in the second step the latter was reduced to vanillin by P. cinnabarinus [50]. The yields have been improved to over 0.5 gl adding cellobiose to the culture medium [51]. This behavior has been ascribed either to the fact that cellobiose is a more easily metabolized carbon source, required for the reduction to occur, or to its action as an inducer of cellobiose-quinone oxidoreductase, which inhibits vanillic acid decarboxylation. 

Ma, X. and Daugulis, A.J. (2014) Transformation of ferulic acid to vanillin using a fed-batch solid-liquid two-phase partitioning bioreactor. Biotechnol. Progr., 30, 207—214. 

The branch pathway of lignin biosynthesis is shown in Fig. 2. The first steps are shared with the general phenylpropanoid pathway. Cinnamic acid is transformed by hydroxylation and methylation to produce acids with different substitutions on the aromatic ring. The 4-coumaric, ferulic and sinapic acids are then esterified by hydroxycinnamate CoA ligase to produce cinnamyl-CoAs, which are reduced by cinnamyl-CoA reductase (CCR) to produce the three aldehydes. These in turn are reduced by CAD to the three cinnamyl alcohols which are then polymerised into lignins. 

L-Phenylalanine,which is derived via the shikimic acid pathway,is an important precursor for aromatic aroma components. This amino acid can be transformed into phe-nylpyruvate by transamination and by subsequent decarboxylation to 2-phenylacetyl-CoA in an analogous reaction as discussed for leucine and valine. 2-Phenylacetyl-CoA is converted into esters of a variety of alcohols or reduced to 2-phenylethanol and transformed into 2-phenyl-ethyl esters. The end products of phenylalanine catabolism are fumaric acid and acetoacetate which are further metabolized by the TCA-cycle. Phenylalanine ammonia lyase converts the amino acid into cinnamic acid, the key intermediate of phenylpropanoid metabolism. By a series of enzymes (cinnamate-4-hydroxylase, p-coumarate 3-hydroxylase, catechol O-methyltransferase and ferulate 5-hydroxylase) cinnamic acid is transformed into p-couma-ric-, caffeic-, ferulic-, 5-hydroxyferulic- and sinapic acids,which act as precursors for flavor components and are important intermediates in the biosynthesis of fla-vonoides, lignins, etc. Reduction of cinnamic acids to aldehydes and alcohols by cinnamoyl-CoA NADPH-oxido-reductase and cinnamoyl-alcohol-dehydrogenase form important flavor compounds such as cinnamic aldehyde, cin-namyl alcohol and esters. Further reduction of cinnamyl alcohols lead to propenyl- and allylphenols such as... 

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