Propolis volatile compounds: chemical diversity and biological activity: a review
Chemistry Central Journal
Propolis volatile compounds: chemical diversity and biological activity: a review
Vassya Bankova 0
Milena Popova 0
Boryana Trusheva 0
0 Institute of Organic Chemistry with Centre of Phytochemistry , Acad. G. Bonchev strl. bl. 9, 1113 Sofia , Bulgaria
Propolis is a sticky material collected by bees from plants, and used in the hive as building material and defensive substance. It has been popular as a remedy in Europe since ancient times. Nowadays, propolis use in over-the-counter preparations, “bio”-cosmetics and functional foods, etc., increases. Volatile compounds are found in low concentrations in propolis, but their aroma and significant biological activity make them important for propolis characterisation. Propolis is a plant-derived product: its chemical composition depends on the local flora at the site of collection, thus it offers a significant chemical diversity. The role of propolis volatiles in identification of its plant origin is discussed. The available data about chemical composition of propolis volatiles from different geographic regions are reviewed, demonstrating significant chemical variability. The contribution of volatiles and their constituents to the biological activities of propolis is considered. Future perspectives in research on propolis volatiles are outlined, especially in studying activities other than antimicrobial.
Propolis; Volatiles; Biological activity; Plant origin
Bees have been in existence for over 100 mill years, and
have become a perennial species that can exploit
virtually all habitats in the world. This evolutionary success is
due to their sophisticated social organization, but it is
due also to the remarkable properties of the bee
products. Honeybees produce high quality foods, building
materials and unprecedented chemical weapons.
Propolis is one of the most fascinating bee product, both
building material and defensive substance. Bees make
use of the mechanical properties of this resinous
substance by applying it for blocking holes and cracks,
repairing combs, strengthening the thin borders of the
comb. On the other hand, they make use of its biological
action: bee glue contains the putrefaction of “embalmed”
intruders, killed in the hive and too large to be carried
out, and it is responsible for the lower incidence of
microorganisms within the hive than in the atmosphere
]. The action against infections is an essential
characteristic of propolis and this fact has been
recognized and used by humans since ancient times. Modern
science focused on propolis after the 1960’s, inspired by
the general interest in natural products. In the last
50 years, numerous studies have revealed versatile
biological activities of propolis: antibacterial, antifungal,
antiviral, cytotoxic, antioxidant, anti-inflammatory,
immunomodulatory among others [
]. Chemical studies
were also performed, including studies on the essential
oils and volatiles of propolis. It turned out that propolis
composition is complex and very much variable in
different regions [
]. Meanwhile, commercial interest to
propolis is growing continuously, it is used as a
component of food additives, cosmetics and over-the-counter
Propolis is a bee product of plant origin, thus at
different geographic locations the source plants might vary
with respect to the local flora. To produce propolis, bees
collect vegetable material and mix it with wax. It is now
generally accepted that bees collect resinous plant
materials, produced by a variety of botanical processes, in
different parts of plants: lipophilic materials on leaves and
leaf buds, mucilages, gums, resins, latices, etc. [
some cases, bees also may cut fragments of vegetative
tissues to release the substances used in propolis
]. Of course, the specificity of the flora at the
site of collection determines the chemical composition
of propolis, including volatile compounds. In different
ecosystems, bees collect propolis from different source
plants, choosing appropriate representatives of the local
flora. Thus, the term “propolis” does not have any
specific chemical connotation unlike the scientific name of
a plant species. Propolis contains secondary plant
metabolites, including volatiles, but they are produced by
different plant species and are not the same all over the
world. In this overview we are going to focus on the
volatiles of different propolis types according to their plant
The importance of propolis volatiles
Propolis volatiles give to the bee glue its specific pleasant
aroma. It is well known that worker honeybees (Apis
mellifera) respond to odors in several behavioral
]. Pheromones emitted by queens and/or
workers communicate a variety of messages and elicit
fairly stereotypical responses in the proper context.
Workers also learn to respond to floral odors, which,
prior to the learning experience, do not typically elicit
such strong innate responses as do pheromones .
Workers learn the association of floral odors with the
nectar and/or pollen rewards offered by the flowers, thus
allowing for future identification of the flowers from
which the rewards can be harvested [
]. No data exist
about the role of odors in foraging for propolis so far. It
seems only logical to assume that the same learning
process occurs in the case of resin collection, taking into
consideration the recent finding of Leonhardt et al., who
have proved that stingless bees in Borneo use volatile
terpenes as olfactory cues to find appropriate resin
The volatile constituents of propolis play an important
role also for human propolis users by contributing to its
pleasant aroma and its biological activity.
Chemical diversity of propolis volatile oils from different
Many authors, in the introductions of their research
articles on propolis claim that propolis contains up to 10%
volatile oils, referring to data from articles published in
the period 1908 – 1948 [
]. More recent publications
however report a much lower percentage, usually up to
1%, rarely 2 - 3%. We have obtained similar results in
our laboratory with samples from many different
The chemical composition of propolis is crucial for
understanding its biological activity. The first study of
propolis essential oils, published in 1974, reported the
identification of only a few constituents: benzoic acid,
benzyl alcohol, vanillin, and eugenol [
]. Further studies
revealed the variability of propolis volatile oils that seemed
to be even higher than the variability of polar propolis
constituents (such as phenolics compounds, flavonoids,
phenolic acids, etc.). As propolis knowledge developed, it
became clear that in the Temperate zone the basic plant
source of bee glue are the bud exudates of trees of the
genus Populus, mainly the black poplar P. nigra. Major
constituents of propolis from the Temperate zone are the
typical poplar phenolics: flavonoid aglycones and esters of
substituted cinnamic acids [
]. The volatile oils however
were more changeable in their chemical composition,
especially with respect to the relative quantities of different
In most European propolis samples studied,
sesquiterpenes predominate in the volatile oils (obtained by
hydrodistillation, simultaneous hydrodistillation-extraction
or headspace), followed by aromatic compounds, such as
benzyl acetate, benzyl benzoate and benzyl alcohol
(Table 1). β-Eudesmol was found to be the major
constituent of propolis volatile oils from France, Hungary, Bulgaria
and Northern Italy [
]. It is interesting to note that
the same sesquiterpene alcohol was found to be the
major constituent of essential oils distilled from leaf
buds of P. nigra . The poplar bud oil, just like
propolis of the above mentioned origins, contained mainly
Of the non-terpenic compounds, benzyl alcohol and
benzyl benzoate were found in these propolis samples.
Benzyl benzoate was present in Hungarian samples, and
also in many other samples from the temperate region
]. Interestingly, benzyl benzoate was not detected
in the volatile oils of poplar buds . In general, it can
be concluded that propolis of poplar origin has also
volatile oils of poplar origin, at least in Hungary, Bulgaria,
France and Northern Italy. Some of the observed
differences could be due to chemical variations of the volatiles
of different poplar subspecies and clones. It is known that
the bud exudates even of the same species have
demonstrated quantitative variability in a wide range.
In other regions of Europe, the chemical composition
of the volatile oils showed some differences (Table 1).
This could be due to the fact that other plant species
could be playing an auxiliary role as propolis bearing
plants: e.g. Cupressus sempervirens in Greece with major
essential oil constituent α-pinene [
], as in the studied
Greek propolis samples [
]. In propolis sample from
Southern Italy (Adriatic coast) α-pinene was also
identified in high percentage and coniferous species were
suggested as the plant source [
]. Recently, monoterpenes
α-pinene, β-pinene and eucalyptol in high amounts were
detected in volatiles of Estonian propolis sample [
Cistus ladanifer and propolis samples [
] from the south
regions of Portugal were characterized with a major
volatile constituent viridiflorol [
*DE Distillation-extraction; HD hydrodestilation; SHS static headspace; HS headspace; DHS dynamic headspace; HS-SPME headspace solid-phase microextraction;
SD steam destilation; UAE ultrasonic assisted extraction; MAE microwave assisted extraction. ** NT not tested; *** NA not available.
There is a specific problem concerning propolis
volatiles coming from hives treated against Varroa mites.
Often the treatment is performed with volatile
compounds, mainly thymol. In such case, the profile of
propolis essential oils is completely unnatural and is
dominated up to 70 – 80% by thymol, which is only
a microcomponent in untreated hives from the very same
In Chinese propolis from Inner Mongolia, the major
constituents of volatile oils were found to be α-bisabolol,
2-methyl-3-buten-2-ol, and 3-methyl-2-butene-1-ol [
High amounts of alcohols 3-methyl-3-butene-1-ol and
3-methyl-2-butene-1-ol, 4-penten-1-yl acetate and the
sesquiterpene α-longipinene were also found in propolis
sample of China [
]. These hemiterpene alcohols and
their esters are typical poplar metabolites; they have
been found also as constituents of headspace volatiles of
poplar propolis from Wales [
Chinese researchers have applied various methods to
obtain propolis volatiles prior to GC-MS analysis. In
headspace volatiles (dynamic headspace sampling, DHS)
of Chinese propolis from 23 regions of China, the main
aroma-active components were acetic acid, 2-phenylethyl
acetate and naphthalene [
]. Solid-phase micro-extraction
combined with GC-MS was used for analysis of
volatiles of Chinese propolis from the Beijing and Hebei
provinces and again acetic acid and phenethyl acetate
were among the main volatile constituents, together
with phenethyl alcohol [
]. Recently, similar chemical
composition, in addition to some sesquiterpenes, was
found for a number of propolis samples from different
regions of China [
]. Their composition was somewhat
similar to the volatiles of gum from poplar trees
growing in China [
]. Using microwave assisted extraction,
the major compounds found in essential oils of Chinese
propolis were long-chain hydrocarbons and only 17%
terpenes and ester derivatives [
Volatile compounds of propolis sample from Turkey
were analyzed by headspace-solid-phase microextraction
coupled with GC/MS. Oxygenated hydrocarbons,
oxygenated sesquiterpenes, aromatic alcohols and esters were the
main aroma-active constituent in North Eastern Anatolian
]. Distinct volatile composition was determined
for propolis sample from South Eastern Anatolia (Malatya),
in which monoterpenes (α-terpinene and α-terpineol) were
the most abundant constituents [
Naik et. al. have reported chemical composition of the
essential oil obtained from Indian propolis by
hydrodistillation. The essential oil was shown to contain long- chain
alkanes (tricosane, hexacosane, heptacosane, heneicosane),
terpenoids (linalool, methyleugenol, geraniol) and phenols
((Z)-ethyl cinnamate) as major groups of compounds [
Outside the Temperate zone, the remarkable
biodiversity of tropical flora reflects in the chemical diversity of
tropical propolis constituents, including volatiles.
South American propolis
The most studied tropical propolis is Brazilian
propolis, and the most popular Brazilian propolis type is
the green or Alecrim propolis originating from the
Asteracean shrub Baccharis dracunculifolia [
Comparative study has been carried out of green propolis
and B. dracunculifolia volatile oils and a similarity in
chemical composition (by GC-MS) detected [
Brazilian green propolis is characterized, like poplar
propolis, with the predominance of sesquiterpenes. Among
the major constituents, nerolidol, β-caryophyllene,
spatulenol and δ-cadinene have been identified.
Caryophyllene, spatulenol and δ-cadinene were the major
compounds in the volatiles of several Brazilian
samples from Sao Paulo, Rio de Janeiro, and Piaui States
]. Green propolis from Minas Gerais State
was rich in nerolidol, β-caryophyllene and selina-3,7(11)
diene . We found that seasonal variations in the
composition of volatile oils of green Brazilian propolis are not
very significant and predominantly quantitatively [
These results were recently confirmed by Nunes et al.
using headspace GC/MS [
]. Nerolidol and the aromatic
compound benzenepropanoic acid were the main
aromaactive constituents in Brazilian green propolis [
Different sesquiterpene composition with major component
longipinene was reported by Li et al. using microwave
assistant extraction of volatiles from commercial Brazilian
In other regions of Brazil, there are propolis types
with source plants other than Alecrim, so their
volatile oils composition is also different. Some samples
from Piaui State had monoterpenes as main constituents:
α- and β-pinene, 1,8-cineole and terpinen-4-ol [
β-Pinene was the major constituents of samples from
Rio de Janeiro State [
]. Predominance of
monoterpenes α-pinene and β-pinene were also detected in the
volatile oil from propolis samples collected from different
regions in Brazil [
]. Similar volatile chemical
composition was found for three propolis samples from Uruguay,
one of them characterized also with high amounts of
Data about propolis volatile oils from other tropical
regions demonstrate the chemical diversity of propolis,
resulting from the specificity of the local biodiversity.
For example volatile oils of Argentinean Andean
], contain high percentage of monoterpenoids,
major constituents o-cymene and limonene. The same
profile of volatile oils was found for the small shrub
Larrea nitida, the exudates of this plant were proved to
be the plant source of the particular propolis. In Yucatan,
α-pinene, hexadecanoic acid and trans-verbenol were
most abundant in propolis volatile oils [
Oxygenated monoterpenes, sesquiterpenes and
oxygenated aliphatic hydrocarbons were the most abundant
constituents in propolis from Ethiopia [
In propolis volatiles from Canary Islands,
sesquiterpenes (nerolidol, spatulenol, ledol) and long chain
hydrocarbons were the major constituents [
Propolis of stingless bees
In Tropics, there are other bees, different from A.
mellifera. They belong to the tribe Meliponini and are known
as “stingless bees”. Stingless bees also collect plant resin
and store it in large deposits within their nests. These
deposits can be used in a similar way as honeybee
propolis: in Brazil stingless bees propolis is a traditional
]. There are only a few studies of the volatile oils
of stingless bees but they demonstrated that their
chemical composition is different from that of honey bees
from the same region, because they use different plant
sources. Some of the samples studied were rich in
monoterpenes, others in sesquiterpenes, and the bee
species could also be of importance for the choice of
plant source [
Biological activities of propolis volatiles
Propolis plant origin is the explanation of the diverse
chemical profiles of its volatile oils. It could be expected
that the observed chemical differences might lead to
different biological activities. The studies dedicated to the
bioactivity of propolis volatiles are relatively scarce, most
of them dealing with antimicrobial properties. Several
authors have confirmed the activity of propolis volatiles
against different microorganisms (Table 1). Among
them are Gram-positive bacteria: Staphylococcus aureus,
Staphylococcus epidermidis, Micrococcus glutamicus,
Bacillus subtilis, Bacillus cereus, Sarcina lutea,
Streptococcus pyogenes, Streptococcus mutans, Streptococcus
], but also
Gramnegative bacteria such as Escherichia coli, Enterobacter
cloacae, Klebsiella pneumonie, Pseudomonas aeruginosa
]. Propolis alcohol extracts are either
not active or of relatively low activity against
Gramnegative bacteria; this has been confirmed by numerous
authors during the last over 20 years. Propolis essential
oils however demonstrated considerable activity against
both Gram-positive and Gram-negative bacteria. Propolis
volatiles were active also against non-pathogenic fungi
and fungal human pathogens Aspergillus niger,
Saccharomyces cerevisiae, Candida albicans, Candida C. tropicalis,
Candida glabrata, Cladosporium cladosporioides,
Cladosporium sphaerospermum [
] as well as against
plant pathogens Cladosporium cladosporioides and
Cladosporium sphaerospermum . Essential oils from
propolis of stingless bees also demonstrated antibacterial
Most of the antimicrobial studies were combined with
chemical analyses of the tested samples and similar
activities were observed for samples with entirely different
chemical characteristics. It is the combination of
compounds with different chemical structure and different
mechanism of action that is important for the biological
activity in the case of propolis. Obviously, volatile oils
also contribute to the complex way in which propolis
fights the infections. A recent study demonstrated
significant synergistic action between propolis alcohol extract
and ginger and mint essential oils against Staphylococcus
aureus and Escherichia coli [
]. Most probably a similar
synergism occurs between polar and volatile constituents
of propolis itself.
Only recently, some other bioactivities have been
reported for propolis volatiles. Japanese researchers revealed
the potential of volatiles of propolis from stingless bees to
stimulate the immune system of elderly patients by
increasing their natural killer cell activity in comparison to
the control group [
]. Essential oils of Chinese propolis
inhibited the proliferation of human colorectal cancer cells
by inducing cell cycle arrest and apoptosis [
essential oils demonstrated therapeutic effects on anxiety
of restraint-stressed mice trough antagonizing the
hyperfunction of hypothalamic-pituitary-adrenal axis and
improving the ability of antioxidation on brain tissue [
The essential oil of Indian propolis was shown to possess
dose dependent repellent activity against the honeybee
Apis florea. Such formulations might be applied by the
beekeepers to keep the honeybees away from pesticide
treated areas in crop fields. This would ensure the safety
of honeybees and their colonies in turn [
The search of further bioactivities of propolis volatile
oils is a promising direction in their study.
It is clear that the knowledge of propolis volatile oils is
far from being exhaustive. Further research is needed to
reveal their chemistry and to scientifically support their
medicinal properties. The most important perspectives
for future research are:
– Systematic studies of volatiles of poplar type and
green Brazilian propolis, to establish their typical
chemical profiles for standardization purposes.
– Studies of the volatile constituents of recently
discovered propolis types: red Brazilian propolis,
Clusia type propolis from South America, Pacific
propolis, etc. Their volatile constituents are almost
– Studies aimed to find out if volatile propolis
constituents play a role as olfactory cues for resin
collection by bees.
– Studies dedicated to revealing the potential and the
importance of propolis volatile oils as bioactive
It is our hope that this review would encourage
some researchers to start such studies in the near
The authors declare that they have no competing interests.
VB, MP and BT performed the data gathering and wrote and approved the
Financial support by the Bulgarian Academy of Sciences is gratefully
Open access provides opportunities to our
colleagues in other parts of the globe, by allowing
anyone to view the content free of charge.
W. Jeffery Hurst, The Hershey Company.
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