Biosynthesis of Plant-derived flavor compounds

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Biosynthesis of Plant-derived flavor compounds

• By Dudsadee Uttapap

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Biosynthesis of plant-derived flavor compounds
References

• 1. Flavor Chemistry and Technology, H.B.
  Heath, G. Reineccius, 1986.
• 2. Flavor Chemistry, D.B. Min,
  http//class.fst.ohio-state.edu/fst820/default.htm
  
• Biosynthesis of plant-derived flavor compounds,
  The Plant Journal (2008) 54, 712732
• Plant Biochemistry http//www.uky.edu/dhild/bio
  chem/lecture.html

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Flavor compounds
Flavor molecules constitute a heterogeneous group
of compounds, with straight-chain,
branched-chain, aromatic and heteroaromatic
backbones bearing diverse chemical groups such
as hydroxyl, carbonyl, carboxyl, ester, lactone,
amine, and thiol functions. More than 700 flavor
chemicals have been identified and catalogued
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Chemical synthesis VS Biosynthesis
Most commercial flavorants are nature
identical, which means that they are the
chemical equivalent of natural flavors but are
chemically synthesized, mostly from
petroleum-derived precursors
Bioproduction, including the extraction from
natural sources, de novo microbial processes
(fermentation), and bioconversion of natural
precursors using micro-organisms or isolated
enzymes
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Biological functions of plant volatiles
associated with defensive and attractive roles

• Compounds emitted by flowers most probably serve
  to attract and guide pollinators
• volatiles might also protect the
  carbohydrate-rich nectar by inhibiting microbial
  growth.
• vegetative plant tissue release volatiles
  following herbivore damage. Some of these
  substances attract arthropods that prey upon or
  parasitize the herbivores.
• Volatiles also act as direct repellents or
  toxicants for herbivores and pathogens.
• In fruits, volatile emission and accumulation
  facilitate seed dispersal by animals and insects.
• vegetative tissues often produce and release many
  of the volatiles after their cells are disrupted.
  These volatile flavor compounds may exhibit
  anti-microbial activity.

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Aromatic compounds responsible for odor and
flavor of fruits comprise
R-COO-R
R-OH
R-CHO
R-CO-R
R-COOH
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Estimated world consumption of selected aroma
chemicals in flavor and fragrance compositions
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Calvin cycle
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Amino acid synthesis
N enters roots as NO3- or NH4. The NH4 is
incorporated into amino acids in roots and leaves
and the amino acids accumulate in proteins. The
main if not sole function of some proteins is to
provide a store of amino acids
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Amino acid synthesis
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Glycolysis
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isoprenoid biosynthesis proceeds either via the
"classical" or most well studied, mevalonate
pathway (cytosolic) (for the synthesis of
sterols, sesquiterpenes, triterpenoids) or via
the non-mevalonate (1-deoxy-D-xylulose-5-phosphate
, DXP) pathway for plastidic isoprenoids
(carotenoids, phytol side-chain of
chlorophylls, plastoquinone, isoprene,
monoterpenes and diterpenes).
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Biosynthesis of flavors in vegetables and fruits
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BIOGENESIS OF FRUIT AROMA
develops entirely during ripening period of plant
Minute quantities of lipids, CHO, protein (amino
acids) are enzymatically converted to volatile
flavors.
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FRUIT FLAVOR COMPOUNDS
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Biosynthesis of fruit volatiles
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Flavorants from carbohydrate metabolism
Only a limited number of natural volatiles
originate directly from carbohydrates without
prior degradation of the carbon skeleton.

• Furanones and pyrones
• fruit constituents

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Furanones and pyrones
Carbohydrate-derived flavor molecules, including
4-hydroxy-2,5-dimethyl-3(2H)-furanone (furaneol),
2,5-dimethyl-4-methoxy-3(2H)-furanone
(methoxyfuraneol), 4-hydroxy-5-methyl-3(2H)-furano
ne (norfuraneol), 2-ethyl-4-hydroxy-5-methyl-3(2H)
-furanone (homofuraneol), 4-hydroxy-2-methylene-5-
methyl-3(2H)- furanone (HMMF) and
3-hydroxy-2-methyl-4H-pyran-4-on (maltol).
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Glycolysis
Flavorants from carbohydrate metabolism
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Flavorants from carbohydrate metabolism
the most interesting is terpene biosynthesis
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Important plant-derived volatile terpenoids.
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Biosynthesis of Terpenes
isoprene is derived from acetyl-CoA
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Classification of Terpenes
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Apocarotenoid formation
Carotenoid substrates are oxidatively cleaved to
yield the apocarotenoid derivatives (right).
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Some of the volatile organic compounds in wine
come from the grape's skin, or exocarp, while
others come from the grape's flesh, or
mesocarp. Organic acids give wine its tartness,
and sugars give it sweetness. Terpenes provide
floral or fruity flavors. Norisoprenoids impart a
honeylike character. Thiols are the sulfur-based
compounds behind complex wine aromas such as
guava, passionfruit or grapefruit but when
thiols go wrong, they can make a wine taste
"funky."
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products acids, alcohols, diketones, ketones,
esters of these compounds.
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Oxidation via Lipoxygenase
Lipoxygenase activity is believed to be the major
source of volatiles in plants.
Lipoxygenase enzymes (dioxygenase) catalyze
reactions between O2 and polyunsaturated fatty
acids
Substrate unsaturated fatty acid (linoleic and
linolenic acids).
Major products volatile C6 and C9 aldehydes and
alcohols
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Linolenic acid-derived flavor molecules.
AAT, alcohol acyl CoA transferase ADH, alcohol
dehydrogenase AER, alkenal oxidoreductase AOC,
allene oxide cyclase AOS, allene oxide synthase
HPL,hydroperoxide lyase JMT, jasmonate
methyltransferase LOX, lipoxygenase OPR,
12-oxo-phytodienoic acid reductase 3Z,2E-EI,
3Z,2E-enal isomerase.
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Fatty acid precursors (Tomato)
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?- and ?-oxidation of fatty acids
the specific pathways in plants are not well
understood
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Formation of pear flavors via beta-oxidation
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Lactones
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Amino Acid Metabolism
their pathways have been barely analyzed in
plants.
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amino acid precursors (Tomato)
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Biosynthesis of amino acid-derived flavor
compounds
(a) Catabolism of branched-chain amino acids
leading to methyl branched flavor compounds, and
(b) postulated biosynthesis of sotolon. Formation
of aldehyde (a) from amino acids requires the
removal of both carboxyl and amino groups. The
sequence of these removals is not fully known and
could be the opposite to that shown or aldehyde
could be formed in one step by aldehyde synthase
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Starting amino acids Tyrosine and phenylalanine
products phenolic/spicy in character
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Shikimic acid formation
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Vegetable flavors
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Formation of flavor in vegetables
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Vegetable Flavor Categories
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Alliaceous vegetables
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Characteristic flavors
not exist in the bulb before processing
are produced when the cellular tissues are
ruptured by cutting or chewing
flavor is produced very rapidly by the action of
an enzyme on the odorless precursors which
coexist in the cells
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Onion and Garlic Flavor
Enzymatic reaction of cysteine derivative
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GLUCOSINOLATES
Glucosinolate precursors are important to the
flavor of both the Brassica and Cruciferae
family Cruciferae family includes radish,
horseradish, mustard.
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Hydrolysis of the glucosinolate
glucosinolate
thioglucosidase
thiocyanate, nitrile, or isothiocyanate glucose
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Natural carbon pools for the productionof flavor
compounds, and the pathways
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Flavorants from carbohydrate metabolism
the most interesting is terpene biosynthesis
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(n total number of carbon atoms)
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• Isoamyl acetate, a strong fruity odor described
  as similar to banana or pear
• 2-Methyl-butyl acetate has a strong apple scent