Improved detection of honey adulteration by measuring differences between 13C/12C stable carbon isotope ratios of protein and sugar compounds with a combination of elemental analyzer - isotope ratio mass spectrometry and liquid chromatography - isotope ratio mass spectrometry (δ13C-EA/LC-IRMS)

The detection of honey adulteration with invert sugar syrups from various C3 and C4 plant sources was realized by coupling an isotope ratio mass spectrometer both to an elemental analyzer and to a liquid chromatograph (EA/LC-IRMS). For 451 authentic honeys measured, the individual delta C-13 values of bulk honey, its protein fraction, fructose, glucose, and di- and trisaccharides ranged from -22.5 to -28.2 parts per thousand and did not show differences (Delta delta C-13) of more than +/- 0.9 parts per thousand (average), with a maximum standard deviation of 0.7 parts per thousand. The Delta delta C-13 (fructose - glucose) value was significantly lower (0 +/- 0.3 parts per thousand). Based on the obtained results and considering a confidence level of 99.7%, the following limits for Delta delta C-13 values of authentic honey are proposed: Delta delta C-13 max.: +/- 2.1 parts per thousand (maximum difference between all measured delta C-13 values); Delta delta C-13 fru - glu: +/- 1.0 parts per thousand; Delta delta C-13 (parts per thousand) protein - honey: >= - 1.0 parts per thousand. The newly developed EA/LC-IRMS method and the purity criteria defined represent a significant improvement compared to existing methods.