| Propolis (bee glue) is a resinous or sometimes wax-like bee hive product collected by honeybees from buds and leaves of plants, mixed with pollen as well as enzymes secreted by bees. Propolis has long been widely used as as a folk medicine, is often used as the active ingredient of health care products and cosmetics, is rich in many biological and pharmacological properties. Since propolis has important biological and biomedical functions, the chemical composition of propolis is interested to both the academic field and consumers.In this study 31 propolis samples collected from various geographic locations in China and one from the United States were divided into four categories by color (yellow, yellow-green, greenish-black, black), and into four categories by locality (monsoon climate of temperate zone, temperate continental climate zone, highland mountain climate zone, subtropical monsoon zone). We determined the concentrations of 15 elements (Ca, Al, Mg, K, Fe, Na, Zn, Mn, Sr, Cu, Cr, Ni as well as toxic As, Cd, and Pb) in propolis by ICP-AES. Principal component analysis, cluster analysis and discriminant analysis were used to find the relationship of elements content with colour and with climatic zones. Furthermore, we used infrared spectroscopy (FTIR) obtained infrared spectra of 45 propolis and 2 gum samples. Data was processed by OMIC software, compared the difference of infrared spectra of those propolis and the difference of propolis with gum, and found the characteristic absorption peaks of gum and propolis.The results shows:1. In propolis, the content of Ca, Al, Mg, K, Fe, Na, Zn are high, the average values were higher than 100mg kg-1; Mn, Pb, Sr, Cd content are low, the average values ranging from 100mg kg-1 to 0.1mg kg-1; The content of As, Cu, Cr, Ni are the lowest, in many samples below the detection limit. Compare of literatures, the Chinese propolis with higher element content in Ca, Al, Mg, K, Fe, Na, Zn, Mn, Pb, Sr, Cd than in the United States and Turkey propolis. Principal component analysis and cluster analysis shows:The element concentration of propolis changes with its color and geographical origins. Black and greenish-black propolis samples are high in element concentrations, especially the toxic Pb and Cd, yellow and yellow-green propolis are low in many elements. Element concentrations are high in propolis from the monsoon climate of temperate zone and temperate continental climate zone, while low in the propolis from subtropical monsoon zone and highland mountain climate zone. Discriminant analysis results are:color correct prediction rate (90.6%) was significantly better than the correct prediction rate of the geographical origins (84.4%). The element content of propolis has closer relationship with color than with climatic zones.2. Propolis and gum have significantly difference in spectra. All propolis with two characteristic peaks in group frequency region,2848.53～2849.08 cm-1 and 2916.76～2917.74 cm-1 (peaks of alkanes), but gum don't have characteristic peak in this region; The characteristic peaks of gum were in 1150～1300 cm-1 (peaks of alcohols, phenols and esters) and 1550～1650 cm-1 (peaks of nitrosyl, amide and alkene). Propolis with many characteristic peaks in 1800～4650 cm-1. Differences in these aspects can be used to distinguish propolis and gum, and can be used to identify true and false propolis. We use Qinghai propolis as a standard sample, in 45 samples, except for Heilongjiang and Hubei (August), the other propolis have high match (match value> 70) with Qinghai. |
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