engleski

Rapid determination of beeswax adulteration by FTIR-ATR spectroscopy

Although Apis mellifera beeswax adulteration has been one of the main quality issues of its production and processing for more than a decade (Bogdanov, 2004), there are still no internationally standardized analytical methods for routine beeswax authenticity control. However, the analytical methods defining beeswax composition criteria for routine authenticity testing based on several classical physico-chemical parameters (Bogdanov, 2009) determined in accordance with European Pharmacopoeia (2008) and the Methods of German Society for Fat Science (DGF), have been employed and nationally established in some countries. Recent report on the feasibility study of a single-reflection Attenuated Total Reflectance Fourier transform infrared spectroscopy (ATR-FTIR) for the detection of beeswax adulterants by Maia et al. (2013), revealed good detection limits of four of the most commonly employed beeswax adulterants ; paraffin, microcrystalline wax, tallow and stearic acid. The reference IR spectra of pure beeswax, main adulterants and different adulteration mixtures, i.e. samples of virgin beeswax (brace combs collected from experimental hives), main adulterants (paraffin, beef tallow) and prepared mixtures of virgin beeswax containing different proportions (5-95%) of paraffin/tallow (n=36), were recorded by FTIR spectroscopy using single-reflection high temperature heated diamond ATR system. Furthermore, in total 27 of comb foundation samples collected from beeswax manufacturers and/or specialized beekeeping shops present in Croatian and neighbouring countries market, were recorded aiming to determine their authenticity based on previously obtained reference IR spectra. Selected classical physico-chemical analyses (determination of acid number, ester number, ester/acid ratio, saponification number and melting point) were performed (EP, 2008) on all samples in order to assess the relationship between IR spectral information and physico-chemical measurands of analysed samples. A factor-based calibration method, Partial Least Squares Regression (PLSR) was used to determine the prediction strength of FTIR-ATR spectroscopy for physico-chemical parameters and proportion of adulterants in studied samples. In this study we demonstrated that an IR fingerprinting enables reliable identification of different beeswax adulteration levels based on indicative IR spectral variations observed in studied specimens. The results of analyses conducted on comb foundations collected in the local beeswax market revealed disturbingly large number of adulterated samples (>50% of analysed samples were adulterated with paraffin) and high level of adulteration (presence of 45-92% of paraffin). The PLSR model performance parameters showed strong predictive power of FTIR-ATR spectroscopy for classical physico-chemical data (calibration R2>0.90) and for adulteration proportion (R2=0.99), which indicates analytical reliability of this method for routine quality control of A. mellifera beeswax. The advantages of this method over commonly used classical ones are that it is fast, reliable, cheap and easy-to-use. Also, FTIR-ATR measurements require no sample preparation (reagent-free method) and only small amount of the sample (0, 1g), which further supports the applicability of FTIR-ATR spectroscopy for routine beeswax analysis.

beeswax adulteration; FTIR-ATR spectroscopy; paraffin share prediction

This work has been supported in part by Croatian Science Foundation under the project NaPro-Flav (8547).