Psicose: first experience with new marker for adulteration
There are many ways to adulterate honey and it is becoming more and more difficult to find out about the fraud. We have therefore broaden our scope of analysis for the authenticity testing of honey and now offer the analysis of psicose, a marker substance for sugar syrups.
Starch-based syrups are used to intentionally adulterate honey and thus increase the yield. By definition, no ingredients shall be added to honey, so these products do not comply with Council Directive 2001/110/EC of 20 December 2001. In addition to a conspicuous sugar spectrum, deviating isotope values and enzymes used for the production of syrups, specific marker substances can prove the presence of syrups.
During the production of these syrups, starch from e.g. maize, sugar beet or rice is metabolized into sucrose, glucose and fructose, whereby the glucose content is very high. With the help of glucose isomerases, the glucose is partially converted into fructose in order to adapt the sugar spectrum and the consistency to that of honey. The by-product of this process is psicose, an isomer of fructose that does not naturally occur in honey and is therefore suitable as a marker substance for syrup addition. A psicose content above 0.1 g/100g indicates the presence of sugar syrups [Kämpf, DLR January 2018, 15-19].
In the literature, psicose is primarily described in syrups made from maize starch (HFCS, high fructose corn syrup). In our investigations, however, psicose could also be detected in samples of pure rice syrup as well as in honey samples which do indicate the presence of sugar syrups from C3 plants.
The analysis is performed by high-performance liquid chromatography associating a Evaporative Light Scattering Detector (HPLC-ELSD, QSI analysis code 40255). A total of 40% of the honeys identified as adulterated by conventional methods and NMR screening contained psicose in concentrations above 0.1 g/100g. The detection of psicose has proved to be a suitable new parameter in the authenticity testing of honey.
Bremen, 12.08.2019 