3.4. Commercial honey samples inspection by the present HPLC method
To check the validity of the present HPLC method, an inspection was carried out on more than 100 commercial honey samples from different nectar sources and producers. All these honey samples were examined firstly by AOAC998.12 method. According to the result of AOAC998.12 analysis, all the inspected samples can be divided into two groups, the pure honey samples 1 > X‰ > À1 and the adulterated honey samples X‰ > 1 or X‰ < À1 (X‰ = d13CHoney‰ À d13CProtein‰). As expected, syrup was detected in most of the adulterated honey samples, X‰ > 1 or X‰ < À1. Contrarily, in some ‘‘authentic’’ honey samples, 1 > X‰ > À1, a high proportion of syrup was detected by the proposed HPLC method. That was confirmed with another starch syrup detection method, thin-layer chromatography (TLC) method (AOAC, 1988), which was only valid when the starch syrup content was higher than 10% (w/w). These misjudged fraud honeys may be adulterated with mixture of C4 and C3 syrups according to a certain ratio.