Identification, quantification and carbon stable isotopes determinations of organic acids in monofloral honeys. A powerful tool for botanical and authenticity control
G. Daniele, Université de Lyon, Institut des Sciences Analytiques, Département Service Central d'Analyse, UMR 5280 CNRS, Université Lyon1, ENS-Lyon, 5 rue de la Doua, 69100 Villeurbanne, France.
The analytical composition and botanical origin of honey are basic data used to determine the quality of this foodstuff. Although proteins are used to characterise the analytical composition of honey, they can be eliminated during its ultrafiltration and, in the case of honeys not saturated with their own pollen, the use of proteins does not work well. As acidity is a well-known characteristic of honey and organic acids are present at around 0.5% in honey, we therefore investigated an alternative method to the protein-based White method, using organic acids as new internal standards instead of proteins.
The qualitative and quantitative analyses of 14 organic acids were carried out by ion chromatography with an electrochemical detector. The 13C/12C isotopic ratios of the honeys, and of the organic acids extracted from them with an anion exchange resin, were determined by isotope ratio mass spectrometry.
Gluconic acid is the predominant organic acid in honey, at between 1.8 and 12.7 g/kg. For fir honey the major acid is galacturonic acid at around 4.6 g/kg. The isotopic ratios of honeys and of their acids are strongly linked. Correlations between the δ13C values of the honey and the acids were significant, and better than those obtained using proteins.
This study has provided a method to differentiate honeys from seven botanical origins, based on organic acid analysis. By combining various organic acid contents and isotopic ratio values through statistical processing by Principal Component Analysis it is possible to differentiate honey samples as a function of their botanical origin. Copyright © 2012 John Wiley & Sons, Ltd.