Propolis is a natural resinous product collected by honeybees from certain plants. It has gained popularity as a food and alternative medicine. Poplar and Baccharis are well known as the source plants of European and Brazilian propolis, respectively. However, the propolis from Okinawa, Japan, contains some prenylflavonoids not seen in other regions such as Europe and Brazil, suggesting that the plant origin of Okinawan propolis is a particular plant that grows in Okinawa. To identify the plant origin of Okinawan propolis, we observed the behavior of honeybees as they collected material from plants and caulked it inside the hive. Honeybees scraped resinous material from the surface of plant fruits of Macaranga tanarius and brought it back to their hive to use it as propolis. We collected samples of the plant and propolis, and compared their constituents by high-performance liquid chromatography with a photo-diode array detector. We also compared their 1,1-diphenyl-2-picryl-hydrazyl radical scavenging activity. The chemical constituents and biological activity of the ethanol extracts of the plant did not differ from those of propolis. This indicates directly that the plant origin of Okinawan propolis is M. tanarius.
We found that different parts of M. tanarius contained antioxidant prenylflavonoids. In particular, not only the glandular trichome but also the leaf contained prenylflavonoids, which indicated that M. tanarius may be developed as a functional plant, because the leaves of this plant can be easily collected.
Polyphenol fractions from twenty-three honey samples of various floral origins were extracted with an Amberlite XAD-2 column, and total polyphenol content and antioxidant properties were determined. The Folin-Ciocalteu method was used to determine total polyphenol content, and antioxidant activity was evaluated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay. Total polyphenol content per 100 g of honey ranged from 17.5 mg (Japanese prickly-ash) to 132.8 mg (peppermint). Peppermint honey had the highest flavonoid content (48.3 mg/100 g) and exhibited the highest antioxidant activity of all samples. A positive linear correlation was observed between honey color and DPPH radical scavenging activity. p-Coumaric acid and kaempferol were isolated and identified as antioxidants from peppermint honey. Additionally, quantification of these compounds in other honey samples was carried out. Peppermint honey contained a large amount of p-coumaric acid (705 μg/100 g) and kaempferol (471 μg/100 g). The potent antioxidant activity of peppermint honey is attributable to the quantities of these compounds, especially kaempferol.
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