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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10

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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