Honey adulteration tests

Honey adulteration tests (article from the National Bee Keeper Magazine, June 2010, v. 18, n.5)

honey results

Preventing contamination of cane sugar in your honey is the key to providing a top grade product for market. Sugar (cane sugar) feeding bees is still recognised as a good way to ensure brood stock survival through colder winter months, or stimulating brood growth in spring. Sugar can also entice bees to stay around particular unifloral varieties for pollination. However, if this cane sugar is transferred from brood boxes or stored in top boxes during the collection phase, then it can “contaminate” and affect the purity of the honey. Other undesirable practises such as honey collection from brood boxes which have been sugar fed also contaminates honey when mixed with higher purity top boxes.

The honey industry is estimated to have exported around 8,600 tonnes of honey in 2009, generating revenue in excess of NZ$100M, of which Manuka honey alone accounted for around NZ$70M of that revenue. However poor knowledge surrounding the effects of excess sugar feeding on honey quality can render a high value product to one which is virtually unsaleable. Furthermore, a basic but crucial sugar test is applied internationally as the main generic C4 cane sugar adulteration test to fulfil export acceptance. This test is now gaining traction in the honey industry as a quality check of New Zealand honey, both for the local and export market. Failure means that these market opportunities are being lost, reputations damaged and brands tarnished.

The “added C4 sugar” test currently offered by GNS Science reports the amount of C4 sugars (cane sugar or high fructose corn syrup) present in the honey using a stable isotope test devised in 1977 for the Association of Official Analytical Chemists (AOAC method 998.12). This sugar test is based on the isotope analysis of the honey and protein. Protein is found naturally in honey and formed by bees through enzymatic breakdown of pollen and nectar. The carbon isotope values of the honey and protein must be virtually identical (within 1 unit ‰) if there are no added sugars. If any sugar is added to the honey, then the carbon isotope value of honey will be changed, while the protein value is unchanged.

Unfortunately it is quite common that unadulterated New Zealand honey, including higher value UMF and active Manuka varieties, fail this AOAC C4 sugar test. Until now, it was largely unknown why these honey samples fail the sugar test which is routinely used worldwide to assess the authenticity of honey. Recent research at GNS Science by Dr Karyne Rogers has uncovered the reasons behind genuine Manuka honey failing these tests. The key problem lies with the internationally recognised AOAC testing method, and could have severe implications for New Zealand Manuka export markets if the method is not modified.

Most overseas importers test honey before purchase. This testing is usually conducted by the importer in European laboratories. A failed sugar test results in loss of sale, which reduces a high quality export shipment into a more modest, lower quality domestic product, and affects future brand confidence and reputation. It is prudent to know what these test results are before sending samples to a purchaser to avoid the embarrassment of a failed sugar test. Furthermore, if your honey does fail this test, it may be a false positive result, meaning that your honey has technically failed, but it is not due to sugar adulteration.

Dr Rogers and her team have found that Manuka honey often has higher levels of pollen compared to other honey types. The pollen levels are artificially high because of the intensive “scrape and centrifuge” extraction method used for Manuka honey collection, compared to “prick and drain” methods often used with lower value honey. Manuka honey is thixotropic (very thick), and because of its high value, producers wish to gain as much product as possible.

Dr Rogers found that pollen contained in Manuka honey had a different isotopic value to the protein. The current AOAC method isolates the protein from the honey for comparison testing, but the current protein isolation method does not remove the pollen beforehand. Protein isolated from Manuka honey with high pollen counts ended up with the pollen contaminating the protein isotopic value. These values were being ‘artificially’ shifted away from the honey, giving a false positive result for added C4 sugars and failing the test. When the pollen was removed before the protein extraction, the honey passed the test. Dr Rogers has shown that a true comparison can now be made between the whole honey and the protein.

The key advantage of the method modification is that it does not preclude the detection of residual sugar feeding of bees or extension of honey with added C4 sugars. In fact, the proposed modification to the AOAC test will reduce false positive tests and improve the overall reliability of results.

Although the pollen ‘contamination’ issue with Manuka honey has only been solved, Dr Rogers has published a peer reviewed paper outlining the problem so that international testing agencies could adopt the modification. Meanwhile the GNS Science Stable Isotope laboratory continues to offer both the traditional and modified methods, and has already assisted several companies to verify their products which have previously returned false positive results.

To prevent rejection of honey, Dr Rogers recommends that any producer who sugar feeds their bees should submit their honey for isotope testing. She adds “blending a batch of honey collected too early from C4 sugar fed bees can contaminate an entire shipment”. To avoid costly mistakes, producers should test each batch to eliminate any questionable batches from the main harvest. Testing will also help producers to understand withholding periods of sugar before collection occurs to minimise the risk of a failed test. Other solutions to this problem could include the removal of brood boxes from the collection boxes or wintering bees using natural products such as honey.

honey storage