Along with the increasing amount of syrup, the original flat baseline at 15.25 min retention time changed into a small swelling slope firstly, and then increased into a higher peak gradually (Fig. 5(b)). The height of the growing peaks correlated linearly with the adulterated amount of rice HFS, S2 in two ranges 2.5–7.5% and 10–100% (w/w), respectively (Fig. 5(c) and (d)). According to Fig. 5(c), as low as 2.5% of HFS in the adulterated honey samples could still be detected using the present HPLC method.
In principle, the linear regression equations in Fig. 5(c) and (d) can be used to calculate syrup content in fraud honey when the analysis and operation conditions are the same. But, according to Fig. 2, the inspected various syrup samples had different content of oligosaccharides of higher DP. Thus, when the equations in Fig. 5(c) and (d) was used to calculate the added amount of syrup in fraud honeys, a positive or negative deviation will be found when the used syrup possesses a higher or lower peak at 15.25 min retention time on HPLC chromatogram. In fact, once a certain amount of syrup was detected in honey sample, this honey can be considered fraud no matter how much syrup was used in the falsification.