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Biosynthesis of Plant-derived flavor compounds. By Dudsadee Uttapap. Biosynthesis of plant - derived flavor compounds. References. 1 . “Flavor Chemistry and Technology”, H.B. Heath, G. Reineccius, 1986. 2 . “Flavor Chemistry”, D.B. Min,

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Biosynthesis of

plant-derived flavor compounds


  • 1. “Flavor Chemistry and Technology”, H.B. Heath, G. Reineccius, 1986.
  • 2.“Flavor Chemistry”, D.B. Min,
  • “Biosynthesis of plant-derived flavor compounds”, The Plant Journal (2008) 54, 712–732
  • “Plant Biochemistry”
flavor compounds
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

chemical synthesis vs biosynthesis
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

biological functions of plant volatiles


  • Compoundsemittedbyflowersmostprobablyservetoattractandguidepollinators
  • volatilesmightalsoprotectthecarbohydrate-richnectarbyinhibitingmicrobialgrowth.
  • 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.









Aromatic compounds responsible for odor and flavor of fruits comprise;







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


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).


Vegetable flavors

develop when tissue damage occurs

(Intact vegetable generally contains few volatiles)

Fruit flavors

are formed during brief ripening period

Biosynthesis of flavors in vegetables and fruits



develops entirely during ripening period of plant

Minute quantities of lipids, CHO, protein (amino acids) are enzymatically converted to volatile flavors.




Malonyl CoA

Amino acid

Acetyl CoA

Fatty acid

Shikimic acid



Mevalonyl CoA

Cinnamic acid

Biosynthesis of fruit volatiles

furanones and pyrones fruit constituents
Furanones and pyrones

“fruit constituents”

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
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)-furanone (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).


Glucose (6C)

2 Pyruvate (3C)


-O2 -O2


Ethanol Lactate

TCA Cycle


Flavorants from carbohydrate metabolism


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 of


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

“the most interesting is terpene biosynthesis”


Biosynthesis of Terpenes

“isoprene is derived from acetyl-CoA”

apocarotenoid formation
Apocarotenoid formation

Carotenoid substrates are oxidatively cleaved to yield the apocarotenoid derivatives (right).


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."



metabolic pathway for lipid biosynthesis plays a significant role in flavor formation.

Alpha-, Beta-oxidation

Oxidation via lipoxygenase

products; acids, alcohols, diketones, ketones, esters of these compounds.


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

linolenic acid derived flavor molecules
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.


Palmitoyl-CoA (16:0)

+ Acetyl-CoA

Myristoyl-CoA (14:0)

  • - and -oxidation of fatty acids

the specific pathways in plants are not well understood


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

Amino Acid Metabolism

their pathways have been barely analyzed in plants.


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


flavor again arises from major metabolic processes - e.g. Lipids, CHO & amino acids.

the precursors, enzymes and end flavors are quite different from fruits.

The role or importance of S compounds to vegetable flavor is quite significant.

Vegetable flavors



Fatty acid

Amino acid

Formation of flavor in vegetables


Genus Allium

Enzymes produce volatiles from derivatives

of cysteine (sulfoxides)

Genus Brassica

Enzymes produce volatiles from glucosinolates

Vegetable Flavor Categories


garlic (Allium sativum L.)

onion (Allium cepa L.)

chive (Allium schoenoprasum L.)

leek (Allium porrum L.)

Alliaceous vegetables


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


Onion and Garlic Flavor

Enzymatic reaction of cysteine derivative



Glucosinolate precursors are important to the flavor of both the Brassica and Cruciferae family

Cruciferae family includes radish, horseradish, mustard.


Hydrolysis of the glucosinolate



thiocyanate, nitrile, or isothiocyanate

& glucose


most of essential oils get flavor from terpenoids (10 carbon)

Limonene - a monoterpene hydrocarbon - is the major terpene in many or most citrus products. Orange > 95% of the essential oil is limonene,

lemon ~ 65% limonene, yet is of little flavor significance.

Citral - oxygenated monoterpene - seldom comprises > 2% of the essential oil of lemon - largely carries the lemon flavor.

Flavorants from carbohydrate metabolism

“the most interesting is terpene biosynthesis”

Isoamyl acetate, a strong fruity odor described as similar to banana or pear
  • 2-Methyl-butyl acetate has a strong apple scent