Ni et al. (2015) synthesized vanillin from glucose and other substrates
(L-tyrosine, xylose and glycerol). The metabolically engineered strain produced
97.2 mg/L vanillin from l-tyrosine, 19.3 mg/L from glucose, 13.3 mg/L from xylose
and 24.7 mg/L from glycerol. Ferulic acid is the best-explored substrate for production of vanillin whose degradation pathways in microorganisms produce vanillin as
an intermediate. Based on the different initial reactions involved in ferulic acid
bioconversion five major pathways can be distinguished in microorganisms which
are (1) CoA-independent retro-aldol reaction, (2) CoA-dependent retro-aldol reaction, (3) CoA-dependent β-oxidation, (4) non-oxidative decarboxylation and (5) a
reductive pathway. Some microorganisms have developed multiple pathways for
bioconversion of ferulic acid. Pseudomonas fluorescens has been reported to metabolize ferulic acid by three pathways which are decarboxylation (Huang et al. 1994),
reduction (Martinez-Cuesta et al. 2005) and via a CoA-dependent retro-aldol reaction mechanism. The retro-aldol mechanism involves elimination of an acetate
moiety from the unsaturated ferulic acid side chain resulting into vanillin formation.
White rot fungi can convert ferulic acid to vanillic acid, which is further converted to
vanillin. Aspergillus niger carries out transformation of ferulic acid into vanillic acid.
In the second step, Pycnoporus cinnabarinus or Phanerochaete chrysosporium
further converts vanillic acid into vanillin (500 mg/L) (Stentelaire et al. 2000).
Several microorganisms have metabolism pathways for formation of vanillin from
ferulic acid (FA) (Tang et al. 2018). In a pathway known as coenzyme-dependent
deacetylation pathway, FA is converted to feruloyl-CoA catalysed by the enzyme,
feruloyl-CoA-synthetase (Fcs). In the next step, enoyl-CoA-hydrolase (Ech) forms
vanillin. The engineered E. coli and other bacterial cells containing Fcs and Ech can
effectively convert FA to vanillin (Yang et al. 2013; Chakraborty et al. 2017). HCHL
gene of Pseudomonas fluorescens, encoding p-hydroxycinnamoyl-CoA hydratase/
lyase, was expressed in two transgenic hairy root (HR) lines of Beta vulgaris. These
HCHL expressing cell lines exhibited conversion of inherently available
phenypropanoid precursor (ferulic acid) into vanillin (Singh et al. 2015).
The chemical constituents of essential oils such as eugenol and isoeugenol can be
converted, by several microorganisms such as Pseudomonas putida, Corynebacterium sp., Arthrobacter globiformis to vanillin (Furukawa et al. 2003; Zhao et al.
2005; Vilela 2018). Barghini et al. (2007) converted ferulic acid to vanillin using
E. coli JM109 cells in which ferulic acid-degrading genes from Pseudomonas
fluorescens BF13 were expressed. The natural pathway of vanillin production in
plants was mimicked in E. coli. The metabolically engineered strain produced
vanillin in different amounts 97.2 mg/L (l-tyrosine), 19.3 mg/L (glucose),
13.3 mg/L (xylose) and 24.7 mg/L (glycerol) (Ni et al. 2015).
Biotransformation approach can be used for the production of vanillin from
certain natural precursors like lignin, eugenol, isoeugenol, ferulic acid and phenolic
stilbenes. Production of flavour compounds can also be carried out using
microorganisms. Vanillic acid has been found as a main intermediate in lignin and
ferulic acid degradation, and in contrast to vanillin, it has found to be accumulated in
remarkable amounts (Andreoni et al. 1995). The first biotransformation process for
production of vanillin was carried out with A. niger ATCC 9142 using isoeugenol.
7 Biotechnological Interventions for Production of Flavour and Fragrance. . .
145
(L-tyrosine, xylose and glycerol). The metabolically engineered strain produced
97.2 mg/L vanillin from l-tyrosine, 19.3 mg/L from glucose, 13.3 mg/L from xylose
and 24.7 mg/L from glycerol. Ferulic acid is the best-explored substrate for production of vanillin whose degradation pathways in microorganisms produce vanillin as
an intermediate. Based on the different initial reactions involved in ferulic acid
bioconversion five major pathways can be distinguished in microorganisms which
are (1) CoA-independent retro-aldol reaction, (2) CoA-dependent retro-aldol reaction, (3) CoA-dependent β-oxidation, (4) non-oxidative decarboxylation and (5) a
reductive pathway. Some microorganisms have developed multiple pathways for
bioconversion of ferulic acid. Pseudomonas fluorescens has been reported to metabolize ferulic acid by three pathways which are decarboxylation (Huang et al. 1994),
reduction (Martinez-Cuesta et al. 2005) and via a CoA-dependent retro-aldol reaction mechanism. The retro-aldol mechanism involves elimination of an acetate
moiety from the unsaturated ferulic acid side chain resulting into vanillin formation.
White rot fungi can convert ferulic acid to vanillic acid, which is further converted to
vanillin. Aspergillus niger carries out transformation of ferulic acid into vanillic acid.
In the second step, Pycnoporus cinnabarinus or Phanerochaete chrysosporium
further converts vanillic acid into vanillin (500 mg/L) (Stentelaire et al. 2000).
Several microorganisms have metabolism pathways for formation of vanillin from
ferulic acid (FA) (Tang et al. 2018). In a pathway known as coenzyme-dependent
deacetylation pathway, FA is converted to feruloyl-CoA catalysed by the enzyme,
feruloyl-CoA-synthetase (Fcs). In the next step, enoyl-CoA-hydrolase (Ech) forms
vanillin. The engineered E. coli and other bacterial cells containing Fcs and Ech can
effectively convert FA to vanillin (Yang et al. 2013; Chakraborty et al. 2017). HCHL
gene of Pseudomonas fluorescens, encoding p-hydroxycinnamoyl-CoA hydratase/
lyase, was expressed in two transgenic hairy root (HR) lines of Beta vulgaris. These
HCHL expressing cell lines exhibited conversion of inherently available
phenypropanoid precursor (ferulic acid) into vanillin (Singh et al. 2015).
The chemical constituents of essential oils such as eugenol and isoeugenol can be
converted, by several microorganisms such as Pseudomonas putida, Corynebacterium sp., Arthrobacter globiformis to vanillin (Furukawa et al. 2003; Zhao et al.
2005; Vilela 2018). Barghini et al. (2007) converted ferulic acid to vanillin using
E. coli JM109 cells in which ferulic acid-degrading genes from Pseudomonas
fluorescens BF13 were expressed. The natural pathway of vanillin production in
plants was mimicked in E. coli. The metabolically engineered strain produced
vanillin in different amounts 97.2 mg/L (l-tyrosine), 19.3 mg/L (glucose),
13.3 mg/L (xylose) and 24.7 mg/L (glycerol) (Ni et al. 2015).
Biotransformation approach can be used for the production of vanillin from
certain natural precursors like lignin, eugenol, isoeugenol, ferulic acid and phenolic
stilbenes. Production of flavour compounds can also be carried out using
microorganisms. Vanillic acid has been found as a main intermediate in lignin and
ferulic acid degradation, and in contrast to vanillin, it has found to be accumulated in
remarkable amounts (Andreoni et al. 1995). The first biotransformation process for
production of vanillin was carried out with A. niger ATCC 9142 using isoeugenol.
7 Biotechnological Interventions for Production of Flavour and Fragrance. . .
145