Honeybees process and produce various substances from plants and flowers, such as honey, pollen, and propolis.[1] The products are components of foods and cosmetics, and they have applications in both traditional and medical practice.[1]-[5]

Propolis is a resinous material collected by honeybees from buds and cracks in the bark of certain plants, typically from poplar, beech, horse chestnut, birch and conifer trees. Bees mix this substance with beeswax and bee enzymes (β-glycosidase) that they secrete during propolis collection.[6]-[9] Propolis contains mainly resin and plant balsam, beeswaxes, essential oils, as well as organic and mineral compounds.[5] Honeybees use propolis to plug holes, straighten inner walls, and soften the walls of their hives for protection against external invaders and hive temperature regulation. Propolis is useful for fending off potential fungal and microbial infections.[2],[5],[10],[11]

In veterinary medicine, propolis is mostly used for its antimicrobial properties. It is also used to enhance livestock growth and productivity.[2] For example, propolis has been reported to increase weight gain among chickens, subsequently improving meat quality. Propolis also increases egg laying rates among layinghens.[9],[12]-[14] Furthermore, propolis has positive effects on livestock feed consumption.[4],[14] It can also be used in veterinary medicine to treat canine fungal otitis and dermal mycosis infections as well as bovine dermatophytosis.[15],[16]

Propolis is also an ingredient of cosmetic creams and lotions. It can be used in shampoos and hair lotions, acne treatments, shaving products, deodorants, antiperspirants, as well as antidandruff and sebum-stabilising agents.[2] In addition to its pharmaceutical uses, propolis may be used as a food preservative, owing to its natural antioxidant and antibacterial effects.[2],[7]

Despite its beneficial properties, propolis also has adverse effects, particularly when used by or administered to sensitive individuals and in high doses. In humans, it can cause allergic and other adverse reactions, including contact dermatitis or oral mucositis.[11],[17],[18]

Data about bees and bee products are available from almost every known period of human history.[19] Propolis has been used by the Egyptians, Greeks, Persians, Arabs, and Romans since ancient times. Moreover, most religious books have spoken about bees and honey.[5],[20] Propolis has been used in traditional and modern medicine as an alternative and supportive treatment for its antibacterial, antifungal, anti-inflammatory, antiviral, antioxidant, gastroprotective, neuroprotective, anti-ulcerative, antispasmodic, chelator, immuno-modulatory, and sedative properties. It has also been used to treat and prevent acne, allergies, liver disease, diarrhoea, diabetes, pain, ageing, malaria, and heart disease.[1],[2],[4],[7],[21]-[24]

More than 300 active compounds have been identified in propolis, with the composition varying by season, plant source, bee species, and altitude.[8] The most important components with pharmacological activity in propolis are flavonoids, like flavones, flavanols, flavanone, and various phenolic and aromatic substances.[2],[4],[6],[8],[9],[11] Flavonoids are not toxic when consumed in fruits and vegetables; they are potentially useful compounds for the human body and protect plants against microbial infection and insect infestation.[22]

Many countries have investigated the chemical composition of their indigenous propolis and identified its biopharmaceutical effects. For instance, propolis has been extensively studied in Europe and South America (especially in Brazil), and there are ongoing detailed studies in China, Japan, Taiwan, and Turkey, among other countries.[8] However, studies on African propolis are few and limited to North African countries, such as Morocco, Algeria, and Egypt.[25]

African vegetation is suitable for beekeeping and, therefore, suitable for propolis production. However, there is a lack of data related to African propolis, and in some countries and regions, including Burundi, there is no available information about the chemical content of the local propolis. Nevertheless, research on propolis in sub-Saharan Africa has shown that, in general, African propolis – like the propolis found in other tropical regions – is rich in terpenoids, including α-amyrine, β-amyrin, α-amyryl acetates, β-amyryl acetates, n-alkanes, n-alkenes, methyl n-alkanoates, and long-chain wax esters, among other compounds.[25]-[30]

The price of propolis varies according to its source and quality. For example, Chinese propolis is offered for sale at about €25 to €50 euros per kg, while the Brazilian propolis is offered at higher prices (€100 to €150 euros per kg).[31] For this reason, propolis production can be beneficial for a nation’s economy in general and particularly profitable for beekeepers. However, for this to be the case, the propolis produced must be of good quality and have the desired pharmacological effects. It is, therefore, necessary to carry out chemical analyses of total phenolic content to assess propolis quality for consumer use. This study aimed to identify, quantify, and characterise the presence of phenolic compounds in Burundian propolis.

Analysed propolis samples were sticky, red, black, and brown with a slight aromatic smell (Table 2). There were also differences between the participating communes in terms of the propolis sample volumes collected, and, overall, the volume of propolis samples collected was small (Table 3). During collection, propolis was generally found in the edge sections of the traps used for harvesting, with the middle sections being empty or slightly waxy. Propolis is typically described as having a fibrous, matte, sticky, and bright appearance, with colours ranging from red, yellow, and green to dark brown depending on the plant source and region; our propolis samples matched these characteristic descriptions. Many researchers have also described the aromatic scent of propolis.[2],[5],[8],[20],[33]-[37]

Among all of the samples collected, only gallic acid was determined at a measurable level. The mean gallic acid concentration was 216.2 μg/g (Table 3), which is low compared to propolis found in temperate regions. In this study, according to the method used, chromatogram peaks were weak, small, and low in number and mainly appeared from 1 minute up to 15 minutes. This finding is in contrast to observations reported by Oruç et al,[8] who – using the same methods as we did – investigated propolis samples from the temperate climate of Turkey and found that peaks were consistent, high, and numerous; their chromatogram peaks appeared between 1 minute and 70 minutes.

Gallic acid is a phenolic compound with antibacterial[38] and antitumour[39] activity. The constituent phenolic compounds found in Burundian propolis are quantitatively and qualitatively different from the propolis components found in temperate climates. Previous studies conducted in sub-Saharan Africa have revealed propolis from this region to contain a high terpenoid content.[26],[30] This has been confirmed by researchers, such as Zhang et al,[30] who investigated propolis samples from Uganda, Tanzania, Malawi, Zambia, South Africa, Cameroon, Nigeria, and The Gambia. They concluded that African propolis was rich in diterpenoids and triterpenoids. Papakroni et al[26] found, for the first time, triterpenes, such as lupennon, β-amirin and lupeol, diprenyl-flavonoid lonchocarpol, and 6,8-diprenyl-eriodictyol in propolis samples from the Democratic Republic of Congo. Rushdi et al[27] found α-amyrin, β-amyrin, α-amyryl acetates, β-amyryl acetates, n-alkanes, n-alkenes, methyl n-alkanoates, and long-chain wax esters in propolis samples from Ethiopia.

The absence of phenolic compounds other than gallic acid in Burundian propolis samples from is in concordance with studies that have reported terpenoids as the main constituents of propolis found in tropical areas, including sub-Sahara Africa. Despite the limitations of our study – including the small number of samples and narrow geographical distribution of propolis – the detection of gallic acid is important in terms of propolis quality and consumption and can be looked at as a starting point for designing new methods for characterising and quantifying the phenolic content of propolis from sub-Saharan Africa.

Acknowledgements: The project was supported by The Commission of Scientific Research Project of Uludag University (Project No: HDP (V)-2017-25). We are grateful Uludag University for providing laboratory and logistical support. We also acknowledge the support of Prof. Songül Sonal, Prof. Murat Cengiz, and Meltem Çaycı.