transform two varieties of tomato, viz. UC82B and CB3. Metabolic analysis of fully
mature tomato fruits showed the accumulation of S-linalool and 8-hydroxylinalool
in ripening fruits, while the other terpenoids such as tocopherols, lycopene, carotene
and lutein remained unaltered (Lewinsohn et al. 2001).
A sesquiterpenoid ‘patchoulol’ (which is a main component of patchouli essential
oil) is generated by the enzyme sesquiterpene synthase from farnesyl pyrophosphate
(FPP). Patchoulol is used as a component in perfumes, incense and natural insect
repellents (Croteau et al. 1987). Sesquiterpene synthase, heterologously expressed in
several organisms such as Saccharomyces cerevisiae (Gruchattka et al. 2013), the
moss Physcomitrella patens (Zhan et al. 2014) and the green microalga
Chlamydomonas reinhardtii (Lauersen et al. 2016), has been used for the fermentative production of patchoulol. Corynebacterium glutamicum is another bacterium
which is considered as workhouse of biotechnology, has been engineered for the
production of patchulol by applying different strategies. In the first strategy, a
farnesyl pyrophosphate-producing platform strain was constructed by combining
genomic deletions with heterologous expression of ispA from Escherichia coli.
Secondly, the limiting enzymes from the 2-C-methyl-D-erythritol 4-phosphate
(MEP)-pathway were overproduced to increase the supply of precursor and in the
third approach plant patchoulol synthase gene PcPS from Pogostemon cablin was
heterologously expressed (Henke et al. 2018). A combinational genetic engineering
strategy was applied in Saccharomyces cerevisiae. It included the change in promoter, knockout of regulator ROX1, inhibition of squalene pathway and
overexpression of tHMGR. The engineered yeast was used for de novo production
of (+)-valencene (Ouyang et al. 2019).
7.3.2.2 Aromatic Compounds in Alcoholic Beverages
Flavours in aromatic beverages are due to higher alcohols and esters, polyfunctional
thiols, lactones and furanones and terpenoids. The flavour profile of alcoholic
beverages is affected due to the medium-chain alcohols, even when present in low
amounts. While fusel alcohols at high concentrations impart off-flavours, low
concentrations of these compounds and their esters impart the basic flavours and
aromas to wine (Belda et al. 2017). Initial fermentation is carried out by a large
number of non-Saccharomyces yeast genera (Candida, Debaryomyces,
Hanseniaspora, Hansenula, Kloeckera, Metschnikowia, Pichia, Lachancea,
Brettanomyces,
Kluyveromyces,
Schizosaccharomyces,
Torulaspora,
Zygosaccharomyces and Saccharomycodes) that contribute significantly to the overall aroma profile of the wine by producing flavour-active compounds (EsteveZarzoso et al. 1998; Romano et al. 2003). Pyruvate, the metabolic intermediate of
glycolysis, is the precursor for the de novo synthesis of higher alcohols.
In yeasts, higher alcohol with aromatic characters is produced via the Ehrlich
pathway, synthesized either from amino acids which are transported across the cell
membrane or through de novo biosynthesis of amino acids and their α-ketoacid
intermediates (Holt et al. 2019). The alcohols such as 2-butanol, 1,2-butanediol and
2-phenylethanol (2-PE) have unique organoleptic properties. 2-phenylethanol
(2-PE), a unique aromatic alcohol, has a delicate fragrance of rose petals (Karami
140
T. Malik and S. Rawat
mature tomato fruits showed the accumulation of S-linalool and 8-hydroxylinalool
in ripening fruits, while the other terpenoids such as tocopherols, lycopene, carotene
and lutein remained unaltered (Lewinsohn et al. 2001).
A sesquiterpenoid ‘patchoulol’ (which is a main component of patchouli essential
oil) is generated by the enzyme sesquiterpene synthase from farnesyl pyrophosphate
(FPP). Patchoulol is used as a component in perfumes, incense and natural insect
repellents (Croteau et al. 1987). Sesquiterpene synthase, heterologously expressed in
several organisms such as Saccharomyces cerevisiae (Gruchattka et al. 2013), the
moss Physcomitrella patens (Zhan et al. 2014) and the green microalga
Chlamydomonas reinhardtii (Lauersen et al. 2016), has been used for the fermentative production of patchoulol. Corynebacterium glutamicum is another bacterium
which is considered as workhouse of biotechnology, has been engineered for the
production of patchulol by applying different strategies. In the first strategy, a
farnesyl pyrophosphate-producing platform strain was constructed by combining
genomic deletions with heterologous expression of ispA from Escherichia coli.
Secondly, the limiting enzymes from the 2-C-methyl-D-erythritol 4-phosphate
(MEP)-pathway were overproduced to increase the supply of precursor and in the
third approach plant patchoulol synthase gene PcPS from Pogostemon cablin was
heterologously expressed (Henke et al. 2018). A combinational genetic engineering
strategy was applied in Saccharomyces cerevisiae. It included the change in promoter, knockout of regulator ROX1, inhibition of squalene pathway and
overexpression of tHMGR. The engineered yeast was used for de novo production
of (+)-valencene (Ouyang et al. 2019).
7.3.2.2 Aromatic Compounds in Alcoholic Beverages
Flavours in aromatic beverages are due to higher alcohols and esters, polyfunctional
thiols, lactones and furanones and terpenoids. The flavour profile of alcoholic
beverages is affected due to the medium-chain alcohols, even when present in low
amounts. While fusel alcohols at high concentrations impart off-flavours, low
concentrations of these compounds and their esters impart the basic flavours and
aromas to wine (Belda et al. 2017). Initial fermentation is carried out by a large
number of non-Saccharomyces yeast genera (Candida, Debaryomyces,
Hanseniaspora, Hansenula, Kloeckera, Metschnikowia, Pichia, Lachancea,
Brettanomyces,
Kluyveromyces,
Schizosaccharomyces,
Torulaspora,
Zygosaccharomyces and Saccharomycodes) that contribute significantly to the overall aroma profile of the wine by producing flavour-active compounds (EsteveZarzoso et al. 1998; Romano et al. 2003). Pyruvate, the metabolic intermediate of
glycolysis, is the precursor for the de novo synthesis of higher alcohols.
In yeasts, higher alcohol with aromatic characters is produced via the Ehrlich
pathway, synthesized either from amino acids which are transported across the cell
membrane or through de novo biosynthesis of amino acids and their α-ketoacid
intermediates (Holt et al. 2019). The alcohols such as 2-butanol, 1,2-butanediol and
2-phenylethanol (2-PE) have unique organoleptic properties. 2-phenylethanol
(2-PE), a unique aromatic alcohol, has a delicate fragrance of rose petals (Karami
140
T. Malik and S. Rawat