The Validity of Protein in Australian Honey as an Internal Standard for C4 Sugar Adulteration

Recent media reports claimed that a large proportion of honey sold in Australian supermarkets was adulterated, although no specific details of the nature of the adulteration were made public. To investigate the basis of these claims, the current study was conducted with samples of Australian honey obtained from supermarkets or direct from beekeepers/small-scale producers. Without evidence to the contrary, it was assumed that the beekeeper honey would be unadulterated. Analysis of these samples using the official AOAC method (998.12) found that a proportion of both supermarket and beekeeper honeys had apparent C4 sugar contents greater than 7% and this proportion was similar to the failure rates reported by popular media. The AOAC test measures the difference in carbon isotopic composition between the honey (mostly sugar) and protein precipitated from the honey and relies on the assumption that nectar (the source of sugar) comes from the same plant species as pollen (the source of protein). Initial results found that most Australian honey failed the AOAC test because the protein was depleted in 13C with respect to the sugar although the sugar was in the normal range (δ13C more negative than – 24‰). A series of experiments investigated the nature of the precipitate obtained from Australian honey and found the weight of precipitate was greater than the amount of protein measured in the honey and the precipitate contained non-protein material. Based on these findings, a modification to the AOAC method is proposed whereby samples, after addition of sodium tungstate and acid, are left unheated for 48 h for a floc to form. This procedure produced a precipitate that was mostly comprised of protein. It is also recommended that the acceptance criteria for Australian honey are increased from 1 to 2‰ difference between the carbon isotopic composition of the honey and the precipitate. Using the modified method and acceptance criteria, the failure rate for Australian honey was no more than 8%, compared to 37% using the official method.