Improved detection of honey adulteration by measuring differences between13C/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 δ13C values of bulk honey, its protein fraction, fructose, glucose, and di- and trisaccharides ranged from −22.5 to −28.2‰ and did not show differences (Δδ13C) of more than ± 0.9‰ (average), with a maximum standard deviation of 0.7‰ The Δδ13C (fructose — glucose) value was significantly lower (0 ± 0.3‰). Based on the obtained results and considering a confidence level of 99.7%, the following limits for Δδ13C values of authentic honey are proposed: Δδ13C max.: ± 2.1‰ (maximum difference between all measured δ13C values); Δδ13C fru —glu: ± 1.0‰; Δδ13C (‰) protein — honey: ⩾ − 1.0‰ The newly developed EA/LC-IRMS method and the purity criteria defined represent a significant improvement compared to existing methods.