Investigation of Temporal Apparent C4 Sugar Change in Manuka Honey

New Zealand manuka honeys are known for their propensity to increase apparent C4 sugar content during storage. Depending on the particular storage regime and the initial content of dihydroxyacetone (DHA) in honey, the ready-to-market product often fails the C4 sugar test because of the above phenomenon. We have used DHA labeled with a radioactive C-14 isotope in a set of honeys subject to an incubation experiment. These honeys were analyzed for DHA, methylglyoxal (MG), hydroxymethylfurfural (HMF), apparent C4 sugars, and C-14 scintillation counts over a period of 18 months. The major conclusion of this experiment is that neither DHA nor MG is responsible for the delta C-13 shift in the honey protein extract. There must be some other yet unknown substance of manuka honey, which binds to the protein and causes negative delta C-13 shift. One identified candidate for such a binding is carbon dioxide.