Plant-derived flavor compounds
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Flavor compoundsFlavor 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 h
ave been identified and catalogued
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Natural Aroma ChemicalsNatural Aroma Chemicals
large variety of acids, large variety of acids, alcohols, alcohols, ketones, ketones, aldehydes, aldehydes, other organic compounds other organic compounds
Cinnamaldehydehttp://www.hellochem.com/xz/img/img0/986.gif
Ethyl vanillinhttp://www.bmrb.wisc.edu/metabolomics/standards/Ethyl_vanillin/lit/jr_167.png 3
Chemical synthesis VS Chemical synthesis VS BiosynthesisBiosynthesis
Most commercial flavorants are ‘nature identical’, which means that they are the chemical equivalent of natural flavors but are chemically synthesized, mostly from petrol
eum-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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Examples of Natural Aroma Examples of Natural Aroma ChemicalsChemicals
Chemical Odor
Diacetyl Buttery
Isoamyl acetate Banana
Benzaldehyde Bitter almond and cherry
Cinnamic aldehyde Cinnamon
Ethyl propionate Fruity
Methyl anthranilate Grape5
Examples of Natural Aroma Examples of Natural Aroma ChemicalsChemicals
Chemical Odor
Ethyl-(E,Z)-2,4-decadienoate
Pear
Allyl hexanoate Pineapple
Ethyl maltol Sugar, cotton candy
Ethyl vanillin Vanilla
Methyl salyicyllate Wintergreen
Limonene Orange
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Biological functions of plant volatilesBiological functions of plant volatiles
Compounds emitted by flowers most probably serve to attract and guidCompounds emitted by flowers most probably serve to attract and guide pollinators e pollinators
volatiles might also protect the carbohydrate-rich nectar by inhibiting mivolatiles might also protect the carbohydrate-rich nectar by inhibiting microbial growth.crobial growth.
vegetative plant tissue release volatiles following herbivore damage. vegetative plant tissue release volatiles following herbivore damage. Some of these substances attract arthropods that prey upon or Some of these substances attract arthropods that prey upon or
parasitize the herbivores. parasitize the herbivores. Volatiles also act as direct repellents or toxicants for herbivores and Volatiles also act as direct repellents or toxicants for herbivores and
pathogens.pathogens.In fruits, volatile emission and accumulation facilitate seed dispersal by In fruits, volatile emission and accumulation facilitate seed dispersal by
animals and insects.animals and insects.vegetative tissues often produce and release many of the vegetative tissues often produce and release many of the
volatiles after their cells are disrupted. These volatile flavor volatiles after their cells are disrupted. These volatile flavor compounds may exhibit anti-microbial activity.compounds may exhibit anti-microbial activity.
““associated with defensive and attractive rolesassociated with defensive and attractive roles””
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Aromatic compounds responsible for od or and flavor of fruits comprise;
Alcohols
Carbonyls
Acids
Esters
Lactones
Phenols
R-OH
R-CHOR-CO-R’
-R COOH
- -R COO R’
R
O CO
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Estimated Estimated world world
consumption consumption of selected of selected
aroma aroma chemicals in chemicals in
flavor and flavor and fragrance fragrance
compositionscompositions
CHO
OH
OCH3
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CO2 + H2O
Photosynthesis Glucose Carbohydrates
GLYCOLYS IS
Acetyl CoA
Citric Acid Cycle
Fatty AcidsLipids
AcetogeninsTerpenesSteroids
Building Blocks
Amino AcidsProteins
synthesisenzymesregulationNucleic
Acidsreproduction
Alkaloids
Phenyl-propanoids
RNA DNA
PRIMARY METABOLISMPRIMARY METABOLISM
SECONDARYSECONDARYMETABOLISMMETABOLISM
SECONDARYSECONDARYMETABOLISMMETABOLISM
h
CO2 + H2O + ATP
Flavonoids
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OCH2OH
OHOH
OHOH
CO2
h
photosynthesis
Glucose(6 carbons)
OCH2OH
OOH
OHOH
OCH2OH
OOH
OHO
CH2OH
OOH
OH
starch nglycolysis
CHCH2OP
OHCHO
C OPCH2
COOH
CCH2OP
OCH2OH
phosphoenolpyruvate (PEP)(3 carbons)
CH3 CO
SCoA
acetyl-coenzymeA (2 carbons)
citricacidcycle
energy (ATP) + CO2 + H2O
CH3 CO
CH2 CO
CH2
polyketidesacetogenins
lipidsfatty acids
mevalonic acid
terpenessteroidscarotenoids
O O
OH CH3
CH OHCH OHCH2OP
CHO
erythrose-4-phosphate
COOH
OH OHOH
shikimicacid
NH2
COOH
anthanilicacid
phenylalaninetyrosine
alkaloids
tryptophan
oxalo-acetate
lysineornithine
asparticacid
nicotinicacid
phenylpropanes
glutamic acid
NH3
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Amino acid synthesis13
isoprenoid biosynthesis proceeds either via the "classical" or most well studied, mevalonate pathway (cytosolic) (for the synthe
sis 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 a
nd diterpenes).14
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Biosynthesis of flavors in vegetables an d fruits
develop when tissue damage occurs (Intact vegetable generally contains few volatil
es)
Vegetable flavors
are formed during brief ripening period
Fruit flavors
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Minute quantities of lipids, CHO, protein (amin o acids) are enzymatically converted to volatile fl
avors.
BIOGENESIS OF FRUIT AROMA
develops entirely during ripening period of plant
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FRUIT FLAVOR COMPOUNDS
AppleApple n-hexanal, ethyl butyrate, 1-propyl n-hexanal, ethyl butyrate, 1-propyl propionate, 1-butyl acetate, trans-2-propionate, 1-butyl acetate, trans-2-hexenal, ethyl 2-methylbutyrate, 2-hexenal, ethyl 2-methylbutyrate, 2-methylbutyl acetate, 1-hexanol, hexen-methylbutyl acetate, 1-hexanol, hexen-1-ol, trans-2-hexen-1-ol, hexyl acetate, 1-ol, trans-2-hexen-1-ol, hexyl acetate, Esters; alcohols; aldehydes; ketone; Esters; alcohols; aldehydes; ketone; acids; including hexanal; ethyl 2-acids; including hexanal; ethyl 2-methyl butyrate methyl butyrate
BananaBanana alcohols; esters, including amyl acetate, alcohols; esters, including amyl acetate, isoamyl acetate, butyl butyrate, amyl b isoamyl acetate, butyl butyrate, amyl b ut yrat e ut yrat e
PeachPeach - -Ethyl acetate, dimethyl disulf ide, cis 3 - -Ethyl acetate, dimethyl disulf ide, cis 3 hexenyl acetate, methyl octanoate, eth hexenyl acetate, methyl octanoate, eth
- yl octanoate, 6 pentyl alpha pyrone, ga - yl octanoate, 6 pentyl alpha pyrone, ga mma decal act one mma decal act one
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Lipids Polysaccharide Proteins/Enzymes Lignins
Aliphatic Terpenes Methyl-Branched AromaticAcidsAlcoholsEstersCarbonylslactones
SesquiterpenesHydrocarbonsAlcoholsCarbonylsmonoterpenes
AlcoholsAcidsEsterscarbonyls
AlcoholsAcidsEsterscarbonyls
Biosynthesis of fruit volatiles
Carbohydrate Amino
acid
Cinnamicaci d
Terpene
Fattyacid -AcetylCoA
MalonylCoA Acetyl C
oA
Pyruvat e
MevalonylCoA
Shikimic acid
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Flavorants from carbohydrate metabolism
Furanones and pyrones
“fruit constituents”
O nly a limited number of natural vol atiles originate directly from carboh
ydrates without prior degradation of the carbon skeleton.
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Furanones and pyrones
- - - -4 25Carbohydrate derived flavor molecules, including hydroxy ,- - - -4 -4 444444-3 (2 ) ( ), 2 ,5 4
- - - - -3 2 4 5 3 2( H) furanone (methoxyfuraneol), hydroxy methyl ( H- - - - - - - -2 4 5 3 2) furanone (norfuraneol), ethyl hydroxy methyl ( H) fur
- - - - - -4 2 5 3 2anone (homofuraneol), hydroxy methylene methyl ( H- - - - - - - - 3 2 4 4) furanone (HMMF) and hydroxy methyl H pyran on (mal
44444
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Glycolysis
Glucose (6C)
2 Pyruvate (3C)
Ethanol LactateTCA Cycle/
Citric Cycle
CO2
+O2
-O2 -O2
Flavorants from carbohydrate metabolism
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Pyruvic acid CH3COCOOH
Acetic acid CH3COOH
Acetyl CoA CH3COSCoA
+ CO2
Malonyl CoA HOOCCH2COSCoA
Malonic Acid HOOCCH2COOH
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“ the most interesting is terpene biosynthesis”
Terpenoids are enzymatically synthesized from acetyl CoA and pyruvate provided by the carbohydrate pools in
plastids and the cytoplasm. Terpenoids constitute one of the most diverse families of
natural products, with over 40 000 different structures ofterpenoids Many of the terpenoids produced are non-volatile and are involved in important plant processes such as membrane
structure (sterols), photosynthesis (chlorophyll side chains, carotenoids), redox chemistry (quinones ) and growth
regulation (gibberellins, abscisic acid, brassinosteroids)
Flavorants from carbohydrate metabolism
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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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CCH2
CH2CH3
OH C
C
O
O
SCoA
SCoA3 acetylCoA C
CH2
CH2CH3
OH C
C
O
O
SCoA
SCoAH
CCH2
CH2CH3
OH C
C
O
O
SCoA
HC
CH2
CH2CH3
OH C
CH2
OSCoA
OH
CCH2
CH2CH3
OH C
CH2
OOH
OH
mevalonic acid
MEVALONIC ACID PATHWAYMEVALONIC ACID PATHWAYFORMATION OF MEVALONIC ACID FROM ACETYL UNITS
NADPH
NADPHH2O
..: : -
(continued next slide) 28
CH2C
S
O
CoACO
OH
CO
CH3 S CoA- CO2
CH2
CS CoA
CCH3
O O
..
CH2C CH2
OCO
CCH3
O
SCoA
POLYKETIDE CHAINS
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CH2
CS CoA
CCH3
O O
CH2
COSCoA
H
CH2
CH2 CH2
CH2C
OHCH3
COOHOH
mevalonic acid
TERPENES ACETOGENINSSTEROIDS
THERE ARE TWO CARBONYL GROUPS IN THE 2-UNIT POLYKETIDE CHAINEITHER ONE CAN REACT
LINEARBRANCHED
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CCH2
CH2CH3
OH C
CH2
OOH
OH
mevalonic acid
CCH2
CH2CH3
O C
CH2
OO
O
P H
P P
:B-Enz2 ATPADPAMP
CH2H
CH2
CH3
OPP
CH3H
CH2
CH3
OPP
3,3-dimethylallylpyrophosphate
isopentenylpyrophosphate
Enz-B: H+
MEVALONIC ACID PATHWAYMEVALONIC ACID PATHWAYThe isopentenyl and 3,3-dimethylallyl pyrophosphate intermediates
These five-carbonintermediates areresponsible for theformation of all theterpenes.
DMAPP IPP
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Classification of Terpenes
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Apocarotenoid formationApocarotenoid formation
Carotenoid substrates are oxidatively cleaved to yield the apocaroten oid 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.
Lipidsmetabolic pathway for lipid biosynthesis plays
a significant role in flavor formation.
Alpha-, -Beta oxidation
Oxidation via lipoxygenase
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Lipoxygenase activity is believed to be the major source of volatiles in plants.
Oxidation via Lipoxygenase
Major products : volatile C6 and C9 aldehydes and alcohols
Substrate : unsaturated fatty acid ( linoleic and linolenic acids).
Lipoxygenase enzymes (dioxygenase) catalyze reactions between O2 and polyunsaturated fatty acids
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- Linolenic acid derived flavor molecules.
AAT, alcohol acyl CoA transferase ; ADH, alcohol dehydrogenase; AE R, alkenal oxidoreductase; AOC, allene oxide cyclase; AOS, allene oxi
de synthase; HPL, hydroperoxide lyase; JMT, jasmonate methyltransferase; LOX, lipoxy
- - - -genase; OPR, 12 oxo phytodienoic acid reductase; 3Z,2E EI, 3Z,2E e nal isomerase.
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Fatty acid precursors (Tomato)
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- and -oxidation of fatty acids
- Palmitoyl CoA (1 6 :0 )
- Myristoyl CoA (1 4 :0 )+ Acetyl-CoA
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
Amino acid metabolism yields short chain aliphatic and aromatic alcohols, acids, carbonyls and esters
They are the primary source of branched chain aliphatic flavor compounds
their pathways have been barely analyzed in plants.
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amino acid precursors(Tomato)
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- (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 a mino groups. The sequence of these removals is not fully known and could b
e the opposite to that shown or aldehyde could be formed in one step by ald ehyde synthase
- Biosynthesis of amino acid derived flavor compounds
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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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Vegetable flavors
- flavor again arises from major metabolic processes e.g. Lipids, CHO &amino acids.
The role or importance of S compounds to v egetable flavor is quite significant.
the precursors, enzymes and end flavors are quit e different from fruits.
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Nonvolatile PrecursorsLinoleic, Linolenic acid Thioglucosinolates Cysteine-sulfoxides Methyl-methionine
Precursor-splitting EnzymesLypoxygenase Thioglucosidases C-S-lyases None (Heating)
CarbonylsAlcoholsOxo-acids
IsothiocyanatesNitrilesS C OThiocyanates
PolysulidesAlkyl-thosulfinates
CH3-S-CH3
Carbohydrate
Fatty acid Amino acid
Formation of flavor in vegetables49
Vegetable Flavor Categories
Genus Allium
Enzymes produce volatiles from derivatives of cysteine (sulfoxides)
Genus Brassica
Enzymes produce volatiles from glucosinolates
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Alliaceous vegetables
garlic ( Allium sativum L.)
onion ( Allium cepa L.)
chive ( Allium schoenoprasum L.)
leek ( Allium porrum L.)51
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 wh ich coexist in the cells
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Onion and Garlic Flavor
Enzymatic reaction of cysteine derivative
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Glucosinolate precursors are important to the flavor of both the Brassica and Cruciferae fami
l y
Cruciferae family includes radish, horseradish,mustard.
GLUCOSINOLATES
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thiocyanate, nitrile, or isothiocyanate &glucose
Hydrolysis of the glucosinolate
glucosinolate
thioglucosidase
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Natural carbon pools for the Natural carbon pools for the productionproduction
of flavor compounds, and the of flavor compounds, and the pathwayspathways
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