GNS scientist’s test confirms the purity of manuka honey

Laboratory testing procedures in importing countries, which were failing manuka honey from New Zelaand, have been found to be flawed giving a higher ‘apparent’ cane sugar level than it actually contains.

An investigation by GNS Science isotope scientist Karyne Rogers has shown the internationally accepted laboratory test designed to detect cane sugar adulteration of honey was often giving false-positive results and causing problems for manuka honey in overseas markets.

A media release from GNS Science said Dr Rogers had developed a modified procedure to give more accurate and reliable results for manuka honey. So far the United States is the only country to adopt the new test criteria. Other countries are expected to follow.

Manuka honey’s unique properties means that the high bioactivity in the honey affects the results of a test used to detect fraudulently added cane sugar, said Dr Rogers, who also led a joint study with participants from 10 international honey testing laboratories to examine the testing issues.

In 2010, six shipments of high bioactive manuka honey worth about $6 million failed border tests, and threatened to close market access into the United States and China. The honey was genuine, but the false-positive test results led to overseas agencies assuming this was because of sugar adulteration, which results in automatic disqualification by importing countries.

“My research has led to the acceptance of new test criteria to accommodate New Zealand honey that was giving false-positive test results,” Dr Rogers said.

“The test itself remains the same, but the interpretation of unusual varieties of honey such as manuka has been changed slightly. Its carbon isotope value is now the main indicator of purity rather than its ‘apparent’ cane sugar level.”

Last year about $110m of honey was exported, mostly manuka honey, but a considerable amount of the harvest was not immediately exportable to markets such as China, Europe and USA because of the testing issue.

A recent consumer survey of manuka honey in Hong Kong has also raised some issues surrounding testing of 55 manuka honey samples, in which 14 exceeded the allowable level of sugar addition.

To be acceptable to importing countries, honey must have a cane sugar content below 7 percent by volume. The flawed method was not measuring the real cane sugar content, and gave only an ‘apparent’ value.

The new criteria allow atypical honey, such as manuka, to have slightly higher cane sugar levels as long as its carbon isotope value is within a certain limit.

Prior to 2010, New Zealand honey products were not routinely tested on arrival in destination countries. However, overseas countries became more vigilant with testing in 2010 in the wake of a sharp increase in honey fraud originating from Asia.

Asian countries were selling inferior sugar-adulterated honey, some of which contained harmful residues and antibiotics, into premium markets world-wide. The increased testing was useful to detect issues with Asian honey, but also found that New Zealand manuka honey was prone to fail the cane sugar test.

As a result of test failures in the past three years, bee keepers have been either holding on to their high-value bioactive manuka honey, or blending it with lower activity manuka containing a lower sugar content to bring down its ‘apparent’ cane sugar levels.

Changing the test criteria will free up about $40m of export manuka honey, which previously did not meet the standard laboratory test.

Dr Rogers has been working with the honey industry for about a decade, providing advice on a range of science-related industry topics. She became more involved in 2010 when significant quantities of manuka honey started failing overseas laboratory tests for no apparent reason.

She is also working with the industry to optimise bee nutrition by assessing different bee forage sources to minimise supplementary sugar and protein feeding, so the bees stay healthy, are more resistant to disease, and produce consistently high quality honey.

She was recently recognised with the National Beekeepers’ Association appreciation award for her significant contributions to the honey industry.

To date her research has been funded by the Ministry for Primary Industries, AGMARDT, and honey industry groups. She is leading a multi-institution request for funding to MBIE to understand the peculiarities of manuka honey and find solutions to ensure continued market access, including authentication and provenance.

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