Propolis, a natural resinous substance collected by honeybees from buds and exudates of plants, has been considered to be used in the beehive as a protective barrier against their enemies. Recently propolis is extensively used in food and beverages to improve health and prevent diseases.
1)The composition of propolis depends on the place and time of collection. Much research and development has been implemented on propolis all over the world. Most of the recent studies are related to Brazilian propolis because it has been reported to possess a characteristic biological activity.2)It is generally accepted and chemically demonstrated that the bud exudates of poplar trees are the main source of propolis from Europe and China.1) On the other hand, the plant origin of Brazilian propolis has not been clarified, since there are no poplar trees in Brazil. Recently Bankova et al. and Midorikawa et al. have reported that the plants of Baccharis species are important sources of Brazilian propolis.3,4) However their studies were not based on the observation of honeybees, and they only compared the chemical constituents of propolis with those of plants.In this study, we observed the behavior of honeybees in Minas Gerais States of Brazil to identify the plant origin of the propolis directly. Further, we comparatively analyzed the constituents of propolis and the plant leaves by HPLC with PDA (photo-diode array) and MS detection.
ExperimentalObserving the Honeybees We observed the honeybees in Minas Gerais, Carvalhopolis in Brazil (SL21.75, WL45.87), where about 20 honeybee colonies were kept. The first and second observations were made on 28-29 Jan. 1998 and on 28-29 Jan. 1999, respectively. We found honeybee workers foraging on plants and recorded the leaf-collecting behavior of honeybees on the plant Baccharis dracunculifolia by VTR.
Sampling of Baccharis dracunculifolia and PropolisWe collected the 18 kinds of young leaves of B. dracunculifolia, which the honeybees were chewing and collecting (sample a), and the propolis from the neighboring honeybees' nest (sample b). We compared the constituents of samples a and b by the following procedure.One hundred milligrams of the B. dracunculifolia leaves and propolis was cut to small pieces and extracted with 5 ml of ethanol at room temperature. After 12 h, extracts were filtered with a 0.45 mm filter prior to 10 ml injection into the HPLC system with PDA and MS detection.Apparatus for Analysis The HPLC system consisted of a SI-1 system (Shiseido, Tokyo, Japan) with a PDA detector. For the analysis of the sample, a Capcell Pak UG 120 (Shiseido, Tokyo, Japan) C18 column (2.0ϫ250 mm, 5 mm) was used. The mobile phase consisted of water with 2% acetic acid (A) and acetonitrile with 2% acetic acid (B). The gradient was 20-80% B in 60 min at a flow rate of 0.2 ml/min. UV spectra were recorded from 195-650 nm at a rate of 0.8 spectrum/s and a resolution of 4.0 nm.MS was performed on an LCQ ion trap mass spectrometer (ThermoFinnigan, CA, U.S.A.) equipped with an ESI (electrospray ioniza...