The origin of natural aromatic materials from Personal Care magazine, Sept. 2011, pp. 73-80

1. Murray Hunter, University Malaysia Perlis, Malaysia FRAGRANCES
The origin of natural
aromatic materials
Plants contain a number of chemicals
based on simple sugars and carbohydrates. Oxygen
Photosynthesis
These include fatty acids, lipids, amino Polysaccharides and
acids, nucleotides, nucleic acids and disaccharides
proteins, etc. Some chemicals act as
primary metabolites which are vital to a
plant’s life and survival or act as precursors Carbon Pentose phosphate pathway
dioxide Glycose
for secondary metabolites and are
concerned with the plant’s interactions with
the surrounding eco-system, principally
acting as deterrents and attractants to
pathogens. Some of these chemicals
Glycolysis
make up essential oils which comprise Nitrates and
of materials from a number of chemical mineral salts Erythrose
groups. Only as recently as fifty years 4-phosphate
ago the isolation of natural materials
had to be undertaken physically, by Phosphoenol
chemical reactions to identify compounds. pyruate Shikimate
Water pathway
This limited the ability to identify more than Aromatic
just a few compounds in essential oils. amino acids
The advent of spectroscopic methods
created a revolution in natural product 6-deoxyxylulose
chemistry which enabled the identification Pyruvate
Hydroxy-
of trace constituents and more detailed
benzoic acid
understanding of the chemistry of plants.
The spectrum of odorous substances is
very narrow where only materials with a Amino acids and
nucleotides
molecular weight below 300-400 and an
appreciable vapour pressure at room
Isoprenoids
temperature have noticeable odours to (terpenoids)
humans. Relatively few organic materials KREBS
CYCLE Alkaloids
have pleasant odours, with the majority
of materials diffusing acetic, propionic, Mevalonic acid
butyric and lactic odours.
Essential oils are not the only chemical
substances found in plants. Metabolites, Phenylpropanoids
like fats, fatty acids, waxes, oils,
coumarins, anthraquinones and alkaloids Acetyl-CoA
are also soluble in ethanol and other
Complex
solvents and can be extracted by alkaloids
distillation. Thus, materials extracted from
plants contain both volatile aromatic and Flavanoids
Triglycerides
odourless substances.
Generally, essential oils can be
physically distinguished from other Malonyl-CoA
compounds because a drop of a volatile oil
on paper will completely evaporate, unlike Complex
Complex
fatty oils. Essential oils are generally a pale isoprenoids
Polyketides flavonoids
to clear or slightly yellowish liquid, mostly (terpenoids)
insoluble in water, with specific gravities Metabolites: I Primary I Secondary
between 0.8 to 1.2. The odour of an
essential oil will resemble the source flora, Figure 1: The plant as a chemical factory.
September 2011 P E R S O N A L C A R E 73

2. FRAGRANCES
made up of a large number of constituents,
sometimes into the hundreds. Some
essential oil odours are dominated by a Shikimate
single constituent, like citral in lemongrass
p-aminobenzoate Aromatic
oil, but most oils rely on a complex mixture
amino acids
of constituents to provide the overall odour
profile.
Chorismate
Constituents in essential oils can be
put into three classes: p-hydroxybenzoate
Those greater than 1%, which are
main constituents.
Those present in parts per thousand, Flavonoids Prephenate
which are minor constituents.
And those less than one part per Anthranilate
thousand, which are trace constituents.
Phenyl-C3
Given the vast number of different odours compounds
and chemical structures in essential oils,
Tryptophan
most compounds are biosynthesised by Phenylalanine
a small number of metabolic pathways.
Although these pathways are common Cinnamic
to all plants, small genetic differences acids
introduce important differences in these
pathways, thereby producing variances in Tyrosine
biosynthesis.1 These numerous reactions
and transformations create exotic fragrance Phenyl-C1
blends, which we call essential oils. compounds
Alkaloids
The plant metabolism
A plant is metaphorically like a “chemical
factory”, producing a wide range of Figure 2: The shikimic acid pathway.
complex compounds to promote growth
and health (primary metabolites), some importance as an intermediate for the synthesis and the production of hydroxy-
for defence and co-existence with the Krebs cycle. This process can be carried benzoic acid through the shikimate
surrounding ecosystem (secondary out both aerobically and anaerobically. pathway, discussed later in this section.
metabolites) and some chemicals for Pyruvate is carried through to the Krebs Finally a pathway, polyamine biosynthesis
reasons that are still unknown to science. cycle which is a series of enzyme catalysed through 6-deoxyxylulose is known to
Plants are complex, open systems chemical reactions, not exclusive to plants, produce a number of precursors for the
with both positive and negative entropy. but all living cells. Pryuvate is combined synthesis of terpenoids.2
Plants, through processes not fully with coenzyme A, to form acetyl CoA, The factors that influence these
understood, are dynamic systems under carbon dioxide and nucleic acids, through complex reactions very briefly summarised
continual change, utilising sunlight, carbon the route of nicotinamide adenine above are still the subject of research
dioxide, oxygen, moisture and soil nutrients dinucleotide (NAD), a coenzyme and and thorough understanding.4 Primary
in the synthesis of various chemical FADH2, an energy-carrying molecule to metabolites provide the precursors for
compounds (see Fig. 1).2 form macromolecules comprising aromatic chemical production in plants.
A plant metabolism is the set of deoxyribonucleic acid (DNA) and ribonucleic They are also the precursors of a number
metabolites which can be categorised acids (RNA), known as ATPs. ATPS play of other compounds that are present in
as primary and secondary. The primary a role in signalling and carrier molecules plants. These types of compounds
metabolites are concerned with the basic for amino acids in protein synthesis. include:
life functions of the plant and provide Mevalonic acid is also formed from acetyl Carbohydrates.
precursors for the production of secondary CoA through the route of 3-hydroxy-3- Lipids.
metabolites. Secondary metabolites are methylglutaryl CoA (HMG-CoA), which goes Amino acids.
concerned with the plant’s interactions to form terpenoid and steroid compounds. Nucleotides.
with the surrounding eco-system and Coenzyme A breaks down to form malonyl Lectins.
principally act as deterrents and attractants CoA which plays a role in fatty acid and Chitinases.
to insects. polyketide synthesis. And various enzymes.
The two most important primary Another pathway, the pentose
metabolite processes are the glycolysis phosphate pathway also processes The metabolic pathways
process and the Krebs or TCA (tricarboxylic sugars through oxidation and synthesis. One of the functions of primary
acid) cycles. Through the breakup of This is an alternative pathway to glycolysis, metabolites is to provide feed-stocks
glucose into other compounds, energy although it also involves the oxidation of for secondary metabolite production.
is also produced. The glycolysis process glucose. Through different processes of This is undertaken through three primary
oxidises glucose produced in the plant dehydrogenation, hydrolysis, oxidative pathways. The mevalonic acid pathway,
by photosynthesis, releasing both energy decarboxylation and isomerisation assisted sometimes called the terpenoid pathway,
and a series of chemicals, of which by enzymes, a number of precursors are is responsible for the synthesis of a wide
pyruvate (pyruvic acid) is of prime produced for fatty acid and amino acid range of metabolites and terpenoids.
74 P E R S O N A L C A R E September 2011

3. The metabolites produced through this Chemically, terpenes, which are very
pathway include the phytol chain found in important in flavour and fragrances, are
chlorophyll and plant growth regulators or very similar to terpenoids, where methyl
pseudo hormones, gibberellins and abscisic groups are adjusted or removed or oxygen
acid, discussed above. The mevalonic acid atoms added.
pathway is an enzymically controlled route The shikimic acid pathway produces
to the formation of mevanolic acid, which precursors for a number of metabolites,
through a number of steps synthesises amino acids, plant regulators, alkaloides
into isopentenyl pyrophosphate (IPP) and and phenolic compounds. This pathway
dimethylallyl pyrophosphate (DMAPP) is unique to plants and continues on from
where they are oxidised, reduced or the pentose phosphate pathway, where
hydrated into a wide range of terpenoids carbohydrate precursors derived from
and steroids. Recently, a mevalonic acid glycolysis as erythrose-4-phosphate react
independent pathway to IPP and DMAPP with phosphoenol pyruvate to form shikimic
has been found utilising deoxyxylulose acid.6 The shikimic acid pathway breaks
phosphate and methylerythritol phosphate into a number of branches as shown in
as precursors.5 The following groups of Figure 2.2
terpenoids are produced by these methods: Approximately 20% of all carbon fixed
Hemiterpenoids: consist of a single in a plant’s leaves is processed through
isoprene unit. Example: phenol. this pathway, which makes up around
Monoterpenoids: consist of two isoprene 30% of a plant’s dry weight.7 Shikimic acid
units. Examples: geraniol, limonene undergoes hydrolysis to break off pyruvic
and terpineol.
Sesquiterpenoids: consist of three
acid and through a number of other steps
converts to chorismic acid, a precursor Combat
isoprene units. Example farnesol. for a number of compounds. Chorismic
Diterpenoids: composed of four
isoprene units. Example: cafestol.
acid is a precursor of salicyclic acid,
a plant hormone. Chorismic acid also
dandruff the
Sesterterpenoids: comprise of five
isoprene units. Example: cericerane.
undergoes a Claisen type rearrangement
to form prephenic acid, which converts into
gentle way.
Triterpenoids: comprise of six isoprene tyrosine and phenylalanine. Tyrosine, an
units. Example: squalene. amino acid, is believed to be involved in
Tetraterpenoids: comprise of eight the photosynthesis process, acting as
isoprene units. Example: gamma- an electron donor in the chloroplasts to
carotone, alpha- and beta-carotenes. reduce oxidised chlorophyll, the signal
Polyterpenoids: long chains of many transduction process in proteins, and
isoprene untis. Example: polyisoprene to assist in producing insect deterring NEW!
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Dual action
Leaf shapes Herbivory (predators)
Increase/
decrease Colours
production
Insects
Special features
Vary (ie spikes etc) Avoid “dangerous”
production metabolites
and
Secondary Produce counter
dissipation
metabolites metabolites
(ie digestion
Responses
Repellents enzymes)
Signal
Attractants Time/spatial
Ingestion inhibitors avoidance
Taste
Camouflage odours
Direct and
indirect
responses
Plant repair
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Figure 3: A plant’s defence system.
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4. FRAGRANCES
to the pigment melanin. Phenylalanine,
Acetyl CoA
also an amino acid derives a number of
flavonoids, lignin and coumarins, and also Mevalonate pathway
assists in producing insect-deterring
3-methylglutaryl CoA
glucosinolates, similar to tyrosine.
(HMG-CoA) Deoxyxylulose
Through another path, anthranilate and phosphate pathway
its derivatives are produced. Little is known
about the purpose of anthranilates in Mevalonate
plants, although they occur as both methyl Glyceraldehyde
and acid forms in many plants. phosphate
Anthranilates are precursors for alkaloids Isoprenyldiphosphate (IPP) and
and tryptophan. Tryptophan is another C5 (1 isoprene unit) dimethyllallyldiphosphate (DMAPP)
amino acid and is a building block for
Pyruvate
proteins and a precursor for niacin, a
number of alkaloids and indole. Finally Monoterpenes Geranyl pyrophosphate
through the shikimic acid pathway, a (GPP)
number of phenyl propanoid compounds C10 (2 isoprene units)
are formed through cinnamic acid by
Sesquiterpenes Farnesylpyrophosphate
elimination of ammonia phenylalanine. (FPP)
Common phenyl propanoids include methyl C15 (3 isoprene units)
chavicol, methyl eugenol, eugenol, methyl
Diterpenes and
cinnamate and vanillin. Phenyl propanoid carotenoids
Geranyl geranyl
accumulation in the plant metabolism is pyrophosphate C20 (4 isoprene units)
still an area where little is known. (GGPP)
Flavonoids and anthocyanins are
pigments and phenolic compounds
responsible for the colours of flowers in Other terpenes
higher plants. Flavones provide the yellow (Triterenes and tetraterpenes) Ionones
and orange colours and the anthocyanins C30+ (6 isoprene units +) (from degraded carotenoids)
are the source of red, violet and blues.
Flavonoids play some role in attracting Figure 4: Mevalonate and deoxyxylulose phosphate pathways to terpene formation.
insects to feed and pollinate, while others
have bitter tastes and repel insects like compounds and also from storage of constituents of essential oils originate and
caterpillars. Flavonoids are also considered foliage after harvesting lead to the also a number of other economic products.
antioxidants. Another important small group formation of a number of compounds. The secondary metabolites are unique to
of polyphenols are the tannins that bind These trace compounds, some desirable each plant species, unlike the primary
and precipitate proteins and may assist in while others undesirable will contribute to metabolites which are common across
the repair of damaged plant tissue, in the odour profiles of a number of essential the flora genus.
conjunction with phytoalexins, which are oils. Unsaturated C6 aldehydes can arise
reported to have antimicrobial properties.8 in green tissue wherever they are cut, Secondary metabolites and
Tannins are very important flavonoids in damaged or attacked by insects, through plant defence systems
teas, wines and some fruits. Tannins are enzymic degradation of linolenic acid.11 The secondary metabolites, primary
used in the preparation of leather, the The degradation of lipids in plants leads to terpenoids, alkaloids, phenolics and
manufacture of colours and as dietary the formation of short chain alcohols and nitrogen compounds evolve within the
supplements. aldehydes, such as the n-hexanol and metabolism and are utilised to improve
Saponins are glycosides of steroids, cis-3-hexanol, compounds that provide a plant’s chances of survival against
steroid alkaloids or triterpenes found green notes to an essential oil. Only with herbivory, primarily insect predators.
primarily in the outer tissue of plants as a much more sensitive analytical equipment Plants utilise a number of attributes
waxy protective layer, although they are over the last few last years have volatile against predators which include physical
also found in other parts including the constituents contributing to the flavour of characteristics, such as surface
roots.9 Many saponins are toxic and fruits and vegetables been discovered. protections,12 the production of complex
thought to be part of the metabolism to However, their enzymic pathways are often polymers that inhibit digestion of the
deter insect predators. Saponins are not still unknown. In some plants, essential plant,13 the production of insoluble
found in all plants. Within the last few oil constituents are free within or bound terpenoids to inhibit digestion, the
years a number of medical and industrial with glycosides within the plant. production of toxins through the alkaloids,
uses have been found for saponins. Some The pathways create the through-fare and the production of volatiles to attract
of the existing uses include foaming agents from which the primary metabolites predators of the insect herbivores.14
in soft drinks and beer, fire extinguishers, produce a set of secondary metabolites Conversely, insect herbivores utilise a
photographic emulsions, and food primarily concerned with the plant’s number of counter measures to overcome
sweeteners. In the medical field, saponins interaction with the immediate plant defences such as detoxification
are used for cough medicines and environment. The secondary metabolite of toxic compounds,15 avoidance
cholesterol. Research is ongoing utilising compounds concern themselves with mechanisms,16 sequestration of poisons18
saponins to fight cancer.10 defences against predators, parasites, and adulteration of the gene pattern.19
Remnants and artefacts from the diseases, interspecies competition and Multiple defence systems are required
pathways and degradation of fatty acids, facilitate the reproductive processes. It is because of different parts of a plant20 and
amino acids, nitrogen and sulphur from the secondary metabolites that the different types of herbivory.21,22 These
76 P E R S O N A L C A R E September 2011

5. FRAGRANCES
defences also assist the plant during times
of stress due to droughts, water logging, Esters
intensive UV radiation and plant damage.
In the reproductive cycle, plants emit
aromatic odours to attract insects to assist Transacylase
in pollination. An overview of the plant (coenzyme)
defence system is depicted in Figure 3.2
Within the eco-system, plants and
insects interact, co-exist and compete
continuously in very complex ways. This is Acids (carboxlic) Alcohols
an evolutionary process as both plants and and acyl CoA
insects modify their defences and attack
strategies continually. Therefore from the Dihtdrofolate reductase Dihtdrofolate reductase
plant perspective, different chemical (coenzyme) (coenzyme)
defences will be utilised at different times
to meet these evolving threats and
stresses.23 Thus as plants grow, they Aldehydes and
change in leaf, branch and other physical ketones
characteristics, including the growth of
flowers and fruits which involves certain Figure 5: The acetyl coa pathway for the biosynthesis of aldehydes, alcohols and esters.
chemical changes within the plant
metabolism, where certain insects can themselves to form various aromatic Terpene hydrocarbons
take advantage.24 This is an important compounds. Methane, a colourless and Terpenes are a very large group of plant
consideration in essential oil production as odourless gas, is the simplest hydrocarbon. hydrocarbons formed by polymerisation of
the desired oil constituent profile may only Some hydrocarbons are non-terpenoid and five carbon atom units (isoprenes) that
develop during a particular part of the plant exist as short chain alcohols and aldehydes form in both chains and rings. They may
lifecycle.25 formed through degradation of be reduced and oxidised into a vast array
phospholipids and fatty acids. Saturated of other compounds including alcohols,
Aromatic compounds homologous straight chain structures are lactones, acids and aldehydes, thus the
found in plants alkanes and their unsaturated forms starting point of synthesis of the majority of
With the exception of compounds that are alkenes. Alkenes can form as isomers, a aromatic compounds. Terpenes are present
products of catabolic breakdowns of lipids, molecule with the same chemical formula in the resinous foliage of leaves. Terpene
amino acids, fatty acids and terpenoids, with the same bonds between atoms, but compounds are heavier than diterpene and
the plant metabolism is directly responsible arranged differently. These are mostly as do not contribute to the odour of essential
for producing aromatic compounds within a stereo isomers in the cis- and trans- form, oils, although they may be present.
plant through a limited number of pathways where the two molecules appear as a
discussed above. Specific and unique “mirror” image of each other. Molecules Monoterpenes
extensions of these pathways exist in with three carbon atoms form straight Monoterpene compounds are found
particular plants, yielding specific aroma chains, where those with four carbons or in nearly all essential oils and have a
compounds found in certain plants. In more can form either straight or branched structure of ten carbon atoms (two
addition there are also a number of chains. Terpenoids usually have a carbon isoprene units) with at least a double
aromatic compounds found in fruits and base of 10, 15, 20 or 30 atoms, where bond. They quickly react to air and heat
vegetables. five carbon atoms are called an isoprene and consequently lack stability and long
Through the plant metabolism, essential unit. Various types of terpene compounds shelf life as they are quickly oxidised.
oils comprise a large number of volatile can be classified according to the number Monoterpenes are present in citrus,
terpenoid and non-terpenoid compounds of isoprene units they contain as Table 1. conifers, herbaceous plants as well as
which are based on hydrocarbons and lists. vegetables and fruits. Monoterpenes are
oxygenated derivatives, although some A single isoprene unit is a hemiterpene, formed through the mevanolate pathway by
contain nitrogen or sulphur derivatives. when two isoprene units link together the conversion of methylallyl pyrophosphate
The hydrocarbons are connected by single, they form a monoterpene, three form a with isopentenylpyrophosphate (IPP) to
double or triple bonds to form higher sesquiterpene, four form a diterpene, form geranyl pyrophosphate, the precursor
molecular weight hydrocarbons, through and so on. of monoterpenes (Fig. 4).2 Compounds
rings or chains. Oxygen, hydrogen, nitrogen, The types of aromatic compounds found like alpha-pinene and beta-pinene are
sulphur, and other carbon atoms attach in plants are: formed through cyclisation from geranyl
pyrophosphate through linaloyl
Table 1. Classification of terpenoids according to isoprene units. pyrophosphate. A large number of
monocyclic compounds, like myrcene
Terpene Classification Carbon Atoms Isoprene Units are also derived through this route.
Hemiterpenes 5 1
Sesquiterpenes
Monoterpenes 10 2
Sesquiterpenes consist of 15 carbon
Sesquiterpenes 15 3 atoms or three isoprene units linked to
Diterpenes 20 4 each other, head to tail. This formation
Triterpenes 30 6 can produce more than 300 different
Tetraterpenes 40 8 hydrocarbon sesquiterpenes.
Sesquiterpenes have great diversity in
September 2011 P E R S O N A L C A R E 77

6. FRAGRANCES
construction, containing up to four
carbocyclic rings. Sesquiterpenes are Primary sulphur
reduction pathway Sulfate
synthesised from farnesylpyrophosphate
which is condensed from Minor sulphur
geranylpyrophosphate, derived from ATP reduction pathway
isoprenyldiphosphate (IPP) and sulphurlyase
dimethyllallyldiphosphate (DMAPP), along Adenylation APS kinase
the mevalonate pathway. Through further
oxidative transformations, a number of
other terpene compounds are formed Adenosin 3’-phosphate
(Fig. 4).2 5’-phosphosulphate 5’-phosphosulphate
(APS) (PAPS)
Ionones APS reductase
Ionones and damascenones are potent
aroma compounds derived from degrading Phosphorised
of high molecular weight terpenes or
carotenoids through oxidation. Carotenoids PAPS reductase
are found in a variety of plants and fruits,
Ferrodoxin- Sulfite
especially berries. dependent sulphite
reductase
Oxygenated compounds
Oxygenated compounds contain oxygen
molecules within their structures.
These include alcohols, aldehydes,
amides, carboxylic acids, esters, ketones, O-acetylserine Sulfide
nitro compounds and oxides. (thiol)lyase
Phenols
O-acetylserine
Phenols are one of the three major
chemical groups in plants along with Cysteine
terpenoids and alkaloids. Phenols originate
from phenylalanine or tyrosine through
the shikimic acid pathway. Phenylalanine Figure 6: The primary and minor sulphur reduction pathway.
ammonia-lyase removes ammonia from
phenylalanine to produce trans-cinnamic way to alcohols.26 Fatty alcohols C8 (octyl, much more pungent than the other
acid. Cinnamic acid itself is not an caprylic) occur in citrus fruits with their aldehydes of the homologous group, which
important odourant but acts as a precursor corresponding esters and aldehydes. are extensively used in perfumery, i.e.,
for numerous aromatic metabolites Alcohol C9 (nonyl, pelargonic) is found in benzaldehyde.
including aldehydes, alcohols, lactones, orange and oakmoss. Alcohol C10 (decyl, Aldehydes are relatively unstable
and esters, outside the phenolic group. capric) is found in orange and ambrette materials which are prone to oxidisation,
Phenols are defined as any compound seed. Alcohol C11 (undecylenic) is found in polymerisation and acetal formation within
having molecules with one or more hydroxy the leaves of Litsea odorifera, and alcohol essential oils. Aldehydes, esters, alcohols
group bonded to a benzene ring. As such, C12 (lauric, dodecyl) is found in lime. and acids can be converted and can revert
many compounds including flavonols, Alcohols do not have the same pungency within plants through transformation and
catechins, anthrocyanins, isoflavones, as their corresponding aldehydes, although oxidation. These reactions are thought to
dihydroflavonols, chalcones, quercetin, as alcohols get higher in molecular weight be controlled through coenzymes. There is
ellagic and tannic acids, vanillin, caffeic their odour intensity increases, until a close interrelationship between acids,
acid, curcumin, courmarins and lignans are nonanol C9, when they start to weaken aldehydes, alcohols and esters within the
also defined as phenols. Phenols oxidise again. Hydroxy hydrogen atoms of Krebs cycle originating from branched
easily and are partly the reason why plant alcohols tend to carry some of the odour amino acids aldehydes are derived from
material darkens after cutting due to this characteristics of aldehydes, while corresponding acids through δ-oxidation
reaction. Phenols in essential oils also maintaining the smoother alcohol notes.27 where it is decarboxylated. Through further
darken on exposure to air and tend to Due to the polarity of alcohols they tend to reduction the aldehyde will convert to its
oxidate. Phenols are acidic due to the be more soluble in water than most other corresponding alcohol and later undergo
–OH group in the molecule. In plants, aromatic compounds. Alcohols transform esterification. This can reverse where the
phenolic compounds usually couple into other compounds including their aldehyde can oxidise to a corresponding
themselves with glucosyl compounds. corresponding aldehydes, acids and acid, later leading to the conversion to
esters through methanol dehydrogenase odd-chain esters.29 This process is capable
Alcohols catalylisation.28 of producing a wide range of aromatic
Alcohols are very similar to phenols and compounds (Fig. 5).2
aldehydes in structure. Alcohols are derived Aldehydes
from aldehydes through dehydrogenase Aldehydes are found in fruits and many Esters
activation. They are also produced plants with their corresponding alcohols Esters are formed from acids and alcohols,
through amino acids through oxidative and esters. Aldehydes have more pungent usually benzenoid, carboxylic and
decarboxylation in ripening fruits. Coenzyme odours than their corresponding alcohols. monoterpenic acids to form esters in
A esters may also be transformed in some Long chain or aliphatic aldehydes are essential oils. Esters are also found in fruit
78 P E R S O N A L C A R E September 2011

7. FRAGRANCES
and vegetables. Examples of esters in that are found in plants. They are some role against pathogens and nitrogen
essential oils are linalyl acetate, benzyl heterocyclic compounds and act as detoxication of plants.38 Little is also known
benzoate and benzyl isobutyrate. Esters hormones in plants.36 about the sulphur pathways in plants, even
are formed through exiting the β-oxidation though sulphur is a necessary compound
acting on acetyl CoA during the Krebs Sulphur compounds for amino acid, proteins, polysaccharides,
cycle.30 A few plants are known to contain volatile lipids and other sulphur containing
sulphur compounds such as dimethyl secondary metabolites.39 Sulphur
Ketones sulphide, dimethyl disulphide and compounds are believed to be derived
Ketones are often present in small dimethylthiophene in garlic, onion, leek through a sulphur reduction pathway
quantities in plants and provide fruity and shallots. Blackcurrant (Ribes nigrum) (Fig. 6).2,40
flavours in fruits. They are highly reactive and buchu (Agathosma betulina) also Volatile aromatic compounds are found
to air and heat and will easily convert to possess sulphur compounds, as well as within the Apiaceae (Umbelliferae),
their corresponding acetals and alcohols. some citrus fruits, coriander, ylang ylang, Asteraceae (Compositae), Cupressaceae,
Ketones are formed through the Krebs rose, peppermint, pepper, geranium, Hypericaceae, Lamiaceae, Lauraceae,
cycle through β-oxidation of alcohols or chamomile, hops and davana.37 Little is Myrtaceae, Pinaceae, Piperaceae,
with acyl CoA activation from carboxyl acids known about the purpose of sulphur Rutaceae, Santalaceae, Zingiberaceae
by hydrolysis causing decarboxylation. compounds in plants except they play and the Zygophyllaceae families. The wide
Lactones
Lactones exist in essential oils as
γ-lactones, a five membered cyclic
ring and δ-lactones, six membered
cyclic rings. Lactones are found in a sense of discovery
herbs, coffee, fruits, dairy products,
with fruity, nutty and hay like odour
profiles. Macrocyclic lactones also
exist in a number of essential oils
and are known as musk lactones.
Coumarins, a lactone in tonka
bean and hay is formed through
hydroxylation of trans-cinnamic
acid to coumaric acid and then
glycosylation, which is stored in
cavities of plant tissue where it
undergoes light-dependent
isomerisation on rupture of the plant
tissue, crystals form.31 Further
synthesis of coumaric acid will give
rise to dihydrocoumarin. Coumarins
are widely used in fragrances for
grassy, hay-like green spicy notes.
Another forms of lactones are
benzofluran derivatives found
as butylphthalides in celery and
angelica.32
Nitrogen compounds
Methyl anthranilate is a very
freshly scented citrus-floral odour Discover what Honeywell’s Asensa® line
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metabolites, amines maybe generally
involved in growth regulation of
plants33 and, along with other
aromatic chemicals,34 methyl
anthranilate has been found to be
both a bird attractant and repellent.35
Amines are very reactive to air and
darken on exposure, as well as being
photosensitive. They can also react
A sense of protection. A sense of feel. A sense of trust.
with aldehydes to form aldimines.
Amines are produced through a
degradation pathway controlled
by amine oxidase enzymes, within
the amino acid pathway. Indole Discover how Honeywell Asensa can add value to your personal care products.
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compounds, aromatic compounds ©2011, Honeywell International Inc. All Rights Reserved.
September 2011 P E R S O N A L C A R E 79

8. FRAGRANCES
variety of different plant metabolisms 23 Futujma P Slatkin M. Introduction, in Futujma P
, ,
producing a diverse range of aromatic Slatkin M, (Eds.) Coevolution 1983; Sunderland,
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