constituent) and glyoxylic acid are still used these days for the chemical synthesis of
vanillin (Esposito et al. 1997). Reimer-Tiemann method (1876) was also adopted;
eugenol (obtained from clove oil) was reacted with potassium hydroxide and
refluxed with an alkaline solution of chloroform and then oxidized by nitrobenzene
to produce vanillin (Havkin-Frenkel and Belanger 2017; Ciriminna et al. 2019). The
reaction between glyoxylic acid and guaiacol is a two-step process: First is the
condensation process which is promoted by base and in the second step, vanillyl
mandelic acid is oxidatively decarboxylated to produce vanillin, catalysed by copper
(II) in an aqueous alkaline medium at 80–130
C (Kumar et al. 2012; Fache et al.
2016). At present, the chemical synthesis of vanillin has been carried out at 5 industrial plants worldwide, fulfilling about 85% global demand of vanillin. The cost of
synthetic vanillin is $10–20/kg, sold mainly to ice cream and chocolate
manufacturers, and to flavour and fragrance companies. For meeting the remaining
demand, vanillin was produced from lignin via an alkaline oxidation process. The
alkaline aqueous solution of lignin is prepared with oxidants (such as nitrobenzene),
at high temperature and pressure. The depolymerisation of lignin releases crude
vanillin containing structurally similar compounds like acetovanillone and
syringaldehyde (Schultz and Templeton 1986; Shakeri et al. 2013).
In 2015, major food companies, including General Mills, Hershey’s, Kellogg’s
and Nestlé, took a vow to eliminate artificial flavours and other synthetic additives
from food items in the USA. At the same time, the bad orchid harvesting season in
Madagascar, the highest producer of vanilla, led to a soar in the market prices
(vanilla beans @$225/kg and pure vanilla price > $11,000/kg). In June 2018, the
price of vanilla beans was further increased to $527/kg. This multi-fold increase in
vanilla price between 2012 and 2018 has to be accomplished by alternative vanillin
production methods which are environment friendly. Although direct bioconversion
of glucose to vanillin has not been known in any naturally occurring
microorganisms, a recombinant E. coli for de novo biosynthesis of vanillic acid
from glucose via a designed shikimate pathway was developed in which vanillic acid
was enzymatically reduced to vanillin by aryl aldehyde dehydrogenase (Li and Frost
1998). In de novo method, biosynthesis of vanillin from glucose was explored in the
yeasts, Schizosaccharomyces pombe and Saccharomyces cerevisiae. Three genes,
viz. 3-dehydroshikimate dehydratase from the dung mould Podospora pauciseta, an
aromatic carboxylic acid reductase (ACAR) from Nocardia and O-methyltransferase
from Homo sapiens, were incorporated in both the yeasts. The production of vanillin
was determined to be 65 and 45 mg/L in S. pombe and S. cerevisiae, respectively,
which was also free from any contaminating isomers and production was carried out
in the usual media and growth conditions (Hansen et al. 2009). Certain natural
substances like lignin, ferulic acid, eugenol, and isoeugenol can be used for the
biosynthesis of vanillin. A gene mining method was devised for producing a
carotenoid cleavage oxygenases (CCO) protein which was named ‘SeNCED’. The
gene from Serratia sp. ATCC 39006 was cloned and overexpressed in E. coli. The
enzyme was used to catalyze the side chain double bond cleavage of isoeugenol and
4-vinylguaiacol to yield vanillin (Tang et al. 2018).
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T. Malik and S. Rawat
vanillin (Esposito et al. 1997). Reimer-Tiemann method (1876) was also adopted;
eugenol (obtained from clove oil) was reacted with potassium hydroxide and
refluxed with an alkaline solution of chloroform and then oxidized by nitrobenzene
to produce vanillin (Havkin-Frenkel and Belanger 2017; Ciriminna et al. 2019). The
reaction between glyoxylic acid and guaiacol is a two-step process: First is the
condensation process which is promoted by base and in the second step, vanillyl
mandelic acid is oxidatively decarboxylated to produce vanillin, catalysed by copper
(II) in an aqueous alkaline medium at 80–130
C (Kumar et al. 2012; Fache et al.
2016). At present, the chemical synthesis of vanillin has been carried out at 5 industrial plants worldwide, fulfilling about 85% global demand of vanillin. The cost of
synthetic vanillin is $10–20/kg, sold mainly to ice cream and chocolate
manufacturers, and to flavour and fragrance companies. For meeting the remaining
demand, vanillin was produced from lignin via an alkaline oxidation process. The
alkaline aqueous solution of lignin is prepared with oxidants (such as nitrobenzene),
at high temperature and pressure. The depolymerisation of lignin releases crude
vanillin containing structurally similar compounds like acetovanillone and
syringaldehyde (Schultz and Templeton 1986; Shakeri et al. 2013).
In 2015, major food companies, including General Mills, Hershey’s, Kellogg’s
and Nestlé, took a vow to eliminate artificial flavours and other synthetic additives
from food items in the USA. At the same time, the bad orchid harvesting season in
Madagascar, the highest producer of vanilla, led to a soar in the market prices
(vanilla beans @$225/kg and pure vanilla price > $11,000/kg). In June 2018, the
price of vanilla beans was further increased to $527/kg. This multi-fold increase in
vanilla price between 2012 and 2018 has to be accomplished by alternative vanillin
production methods which are environment friendly. Although direct bioconversion
of glucose to vanillin has not been known in any naturally occurring
microorganisms, a recombinant E. coli for de novo biosynthesis of vanillic acid
from glucose via a designed shikimate pathway was developed in which vanillic acid
was enzymatically reduced to vanillin by aryl aldehyde dehydrogenase (Li and Frost
1998). In de novo method, biosynthesis of vanillin from glucose was explored in the
yeasts, Schizosaccharomyces pombe and Saccharomyces cerevisiae. Three genes,
viz. 3-dehydroshikimate dehydratase from the dung mould Podospora pauciseta, an
aromatic carboxylic acid reductase (ACAR) from Nocardia and O-methyltransferase
from Homo sapiens, were incorporated in both the yeasts. The production of vanillin
was determined to be 65 and 45 mg/L in S. pombe and S. cerevisiae, respectively,
which was also free from any contaminating isomers and production was carried out
in the usual media and growth conditions (Hansen et al. 2009). Certain natural
substances like lignin, ferulic acid, eugenol, and isoeugenol can be used for the
biosynthesis of vanillin. A gene mining method was devised for producing a
carotenoid cleavage oxygenases (CCO) protein which was named ‘SeNCED’. The
gene from Serratia sp. ATCC 39006 was cloned and overexpressed in E. coli. The
enzyme was used to catalyze the side chain double bond cleavage of isoeugenol and
4-vinylguaiacol to yield vanillin (Tang et al. 2018).
144
T. Malik and S. Rawat