Propolis is composed principally of resin and wax. Its colour can vary enormously. In temperate climates it ranges from a light yellow or brown to a dark brown colour, often with a reddish hue. Propolis produced in tropical climates can range from the light brown-green of Brazilian propolis to the black and dark red of some Cuban varieties. Propolis tends to become darker the longer it is in the hive. Fresh propolis appears as a red tinge on the new white comb constructed by the bees. The colour of propolis also varies according to the trees and plants harvested, as well as the types of bees gathering it. Propolis collected by black bees tends to be darker in colour.
You can ﬁnd propolis most easily at two sites in the hive—at the entrance, which is constructed almost entirely from propolis, and along the sides of the frames, where it is often deposited in larger quantities in zigzag patterns. Some believe these larger deposits act as a kind of storage facility before being moved to ﬁll cracks or openings, or to be rendered down into a ﬁner, more liquid form for use elsewhere in the hive.
At moderate temperatures propolis becomes soft and malleable when handled but when frozen becomes brittle. Propolis turns to a liquid at temperatures between 70–100°C.
How Do Bees Collect Propolis?
Most beekeepers and researchers now believe that the resins in propolis are collected directly by the bees from trees, shrubs and plants. However, this is not the only theory that has been put forward. In 1907 Kustenmacher,1 a German bee researcher, sug gested that propolis was largely derived from pollen granules. Kustenmacher believed that that the bees took pollen granules into a section of their intestine where the granules would swell to ﬁve times their size as they absorbed water. As the granules burst open they released a plasma which he believed the bees used to feed their young.
The pollen husks that remained were processed into a balsam, which was then excreted. This balsamic excretion was then mixed with other discarded pollen husks, waxes and detritus from the hive, forming the basis of propolis. The resulting more solid, brownish mixture could then be transported around the hive. Support for this theory has come from some experiments, which show that even where bees are deprived of resinous materials but not pollen, propolis is still produced. Further support also comes from the observation that maximum production of propolis always coincides with times of greatest pollen production.
Whilst not all of Kustenmacher’s theory has been discarded, the advent of modern biochemical analysis has very much weakened it. For example, research has shown that few, if any, of the chemicals released in the breakdown of pollen end up in propolis.
By far the most plausible and now most popular theory was put forward by Rosch and others, again in the early part of this century. Rosch observed bees removing sections of resin from trees with their mandibles, which they used to further break down the resinous lumps. The resin was then passed from the forelegs to the mid-legs of the bee, continuing to be worked on and gradually formed into a pellet as pollen is, before being deposited into the bee’s pollen baskets. The bees then ﬂew back to the hive where other bees removed the propolis and transferred it to storage sites or applied it in the hive for a variety of purposes.
A combination of the two theories was suggested by Phillip in the 1930s. He argued that there were two kinds of propolis, one produced in the way described by Kustenmacher and the second, according to Rosch, by the collection of resin from external sources. Phillip maintained that the propolis produced from pollen had the most important use in the hive, covering and sterilizing the cells into which the queen lays her eggs. Propolis collected from external sources had a secondary use, more as a building material within the hive—strengthening the comb and ﬁlling cracks and crevices. Personally, I feel that there may be something in the Phillip theory which does explain the two different uses of propolis, but I think we will have to wait for further, one imagines difﬁcult, research, for a deﬁnitive answer.
The Importance of Resins
One thing is certain—resins derived from one source or another, form a major ingredient, around 50 per cent, of propolis. From the outset, the bees are collecting a material which the plant world already relies on to maintain its health and integrity.
We know resins have an important role to play in the immune defence systems of trees and plants. We have all seen how, if a tree is damaged or cut, the resins pour out in order to seal up the
‘wound’, to stop the tree bleeding. Many of these resins themselves have a hallowed place in natural medicines. Two out of the three gifts taken by the Wise Men to the infant Jesus at his birth were tree resins—frankincense and myrrh. Frankincense and myrrh have well-documented anti-inﬂammatory properties and are used to treat a variety of health problems, including rheumatism and arthritis, as well as for bronchial and respiratory complaints. Other resins, including poplar bud resin, benzoin and pine resin, have ﬁgured in their own right as part of the natural medicine chest, for similar reasons. It is not surprising therefore that the honeybee should seek out these and other resins as a valuable base material for propolis.
Do Bees Create Something Unique in Propolis?
How much the bees work on the resins they collect from trees and plants, transforming them into propolis by processing them both outside and inside the hive, is still a matter of debate. Some researchers believe the bees take an active part in transforming resin into propolis with the help of glandular secretions produced as they collect the resin.4 These secretions contain enzymes which metabolise the resin. A Cuban study in 19905 showed that the resins collected by the bees are at least in part metabolised by them, and Greenaway6 in 1997 suggests that by adding saliva during the scraping and chewing of the resins, new elements, e.g. sugars, are produced. The same research showed that the chemical structure of the bioﬂavonoids in tree resins collected by the bees is changed by the time they appear in propolis. Others researchers argue that it is the tree or plant resins, pure and simple, which give propolis its unique protective and therapeutic properties within the beehive. My own feeling is that the extraordinary capacity of the honeybee to transform a range of simple raw materials, pollen and nectar for example, into highly complex substances like honey and royal jelly supports the idea that the bee is actively contributing to the creation of something new and unique.
The beehive is a symbol of how simpler substances derived from the lower order of the plant world are elevated and transformed by the bee into substances appropriate for a higher order of existence. In comparing the wide range of therapeutic properties which pro polis provides for man with the often narrower range of therapeutic properties possessed by single plants or herbs, we are made aware again of the quantum leap in complexity and sophistication which differentiates the plant from the animal world.
The Poplar Tree Myth
One commonly held belief about the origin of propolis is that it is derived solely from the resin of the poplar tree. This is not the case. Although the poplar tree is a favoured source of resin, where available, bees will collect from a wide variety of trees, shrubs and plants depending on what is locally available. Why bees choose one source above another remains a mystery. We can only assume that bees possess a sense of attraction which guides them to those trees, shrubs or plants most able to provide them with the structural and pharmacological properties they need.
Not All Bees Collect Propolis
Only the Western honeybee (Apis mellifera) is known to forage for propolis whilst the Asian species of honeybee do not. Apis mellifera is present throughout the world and it is clear that it is able to adapt to whatever ﬂora is available to collect the resins essential for propolis. The colour, smell and composition of propolis is determined by the dominant sources of resins in the region.
Some tropical bees, Apis cerana, Apis dorsata and Tropical Apis mellifera, make no use of propolis at all, and Carniolan bees are reported to use wax instead of propolis. The tropical stingless bees or Meliponine do collect a resinous substance similar to propo lis, which they use to seal up the hive and to create honey and pollen storage vessels. However, little is known about this species and by far the bulk of research into propolis has been conducted into Apis mellifera.
Exactly why some bees collect propolis and others do not remains unclear. Is it perhaps because some bees do not require the sterilising, antibiotic properties that propolis provides or do they utilise other products for these purposes? Could it be that Phillips and Kustenmacher are right after all and that the most important sterilising function in the hive is provided by propolis derived from the breakdown of pollen? May it also be that bees which are truly native to southern climates do not have the same need for, and therefore have not evolved a system for collecting, the cruder ‘double glazing’ variety of externally-gathered propolis. Perhaps where they have a need for a building material rather than an antibiotic material, instead of using resin they substitute other materials like soil and other debris, as do the stingless bees of Africa or use wax alone as do Carniolan bees.
Cuban researchers are currently looking at the reasons why propolis produced in the southern hemisphere by the Western Apis mellifera contains a different package of microelements to that produced in the northern hemisphere. It may be that this work will somehow lead us to a better understanding of why other types of bees, which are truly indigenous to tropical climates, do not produce propolis at all.
We must assume evolution plays some part in the propolis story. Some bees, we know, are noted for collecting propolis more actively than others; in particular Grey Mountain Caucasian bees collect more than dark forest bees. Italian, Ukranian and Far East bees collect very little propolis Theo Frederich,7 a beekeeper on Vancouver Island, British Columbia, tells us that, ‘today’s bees propolize less than they used to, many of us will remember the old days with the old black bees that glued everything solid, when you could literally scrape off a quarter pound of propolis from the entrances.’ He goes on to tell us that those modern beekeepers have bred queens speciﬁcally to produce less propolis in order to make their job easier.
What Does Propolis Contain?
Whether or not there are two distinct forms of propolis the majority of research which has explored its components, has been carried on propolis harvested externally. Whilst resin and wax are the two major ingredients, research, particularly over the last 15 years has revealed an increasingly complex package of additional microele ments. In 1990, at Oxford, Greenaway8 identiﬁed 150 distinct com pounds in propolis. More recent studies have identiﬁed a further
30 new compounds. As our chemical analytical equipment improves, so further biochemical dimensions of propolis are revealed and it seems likely that more elements yet remain to be discovered.
The constituents of propolis can vary considerably according to where in the world the propolis is harvested and the plants and trees the bees have visited. Content can also vary according to season of collection and even the time of the day the bees collect the resins. Table 1 shows the ﬁve major compounds in propolis
Table 1: The Principal Compounds in Propolis
|Waxes and fatty acids||25–35%|
|Other organics and minerals||5%|
The resins contain the majority of the ﬂavonoids—perhaps as many as 40—found in propolis along with a number of phenols and acids. Flavonoids are found everywhere in the plant kingdom, especially in fruit and vegetables. Propolis contains particularly high quantities of a large range of ﬂavonoids and it is these that have attracted most attention from researchers seeking the so-called ‘actives’ in propolis, i.e. those elements thought most responsible for particular pharmacological actions. We shall return for a more detailed look at the role of ﬂavonoids later when we look at the pharmacological and physiological effects of propolis.
Most of the waxes and fatty acids present in propolis are derived from beeswax but many of them are of plant origin. The role of the waxes in propolis has been neglected. When propolis is reﬁned the waxes are generally removed. They are, however, an integral and important part of propolis and contain a range of micro elements thought to be important in treating burns. Clinical trials using beeswax to treat burns are currently being carried out in a hospital in the south of England.
The range of essential oils found in propolis depends on the ﬂora harvested by the bees. Petri,9 a Hungarian researcher, has compared the essential oils collected from propolis with the oil from poplar bud, that favourite source of resin for the bees. Micro biological tests showed similar moderate activity against some bacteria and fungi.
The small amount of pollen found in propolis is responsible for its protein content. Gabrys,10 a Polish researcher, found 16 amino acids present in propolis at more than 1 per cent. Of the total amino acids present, arginine and proline together made up 45.8 per cent. A further eight amino acids were present in traces. Gabrys suggests that the ability of propolis to stimulate tissue regeneration is due to the presence of arginine because of its role in stimulating the production of nucleic acid.
Around 14 mineral trace elements are found in propolis, of which iron and zinc are the most common. Other minerals found include gold, silver, caesium, mercury and lead.
In 1994 high levels of lead were found in propolis on sale to consumers in the UK. Explanations for this ranged from atmo spheric pollution to the use of hives painted with lead paint. Paradoxically however, it appears that resin has an unusual afﬁnity for lead and may even remove it from the body. Felix Murat11 in his book Propolis—The Eternal Natural Healer, tells an interesting story of how lead ingested from car exhaust fumes in Athens can be eliminated from the body by drinking the local wine, retsina! Murat explains that when the grapes are pressed and the wine ﬁrst starts to ferment, ‘a certain amount of virgin resin, fresh as it comes from the tapped pine trees, is poured into the fermenting vat.’ The resin in retsina, with its afﬁnity for lead, and also mercury, absorbs the metal, turning it into harmless compounds which are eliminated through urination.
By a strange twist the most advanced propolis reﬁning plant in the world, recently built in Arizona and developed to remove lead and other heavy metals from propolis, utilises newly developed supercolloidal technology which involves passing liquid propolis through a column charged with resin. The lead particles are selectively attracted to the resin. Perhaps the real question here, however, is whether the metals, like lead, which propolis appears to attract are there for some positive purpose or whether this natural afﬁnity just happens to be operating as a natural collector of lead in the environment.
Finally, a variety of additional organic compounds are also found in propolis. These include ketones, lactones, quinones, ster oids, benzoic acid and esters, vitamins and sugars. As research adds further elements to the growing list of those already known to be in propolis, so the biochemical and pharmacological mystery of propolis deepens. But before we explore this mystery as it relates to our health, let’s remain a little longer with the bee itself and examine how it uses propolis in the hive.