By Jessica Burdg, Contributing Science Writer, Laboratory Equipment Magazine
The common phrase “things aren’t always what they seem” can apply to a plethora of situations over the course of your lifetime—but how about a trip to the supermarket? Food authentication, especially for items such as honey and olive oil, is becoming more prevalent due to a rise in counterfeiting and mislabeling. Laboratory professionals have long answered the food validity call, and their work continues to evolve to meet the needs of the respective industries.
Testing honey’s authenticity
Two novel ways to test for the authenticity of marketed origin in honey include melissopalynology, the study of pollen contained in the substance, and NMR spectroscopy.
Vaughn Bryant is the Director of the Palynology Laboratory and a professor in the Department of Anthropology at Texas A&M University. He analyzes the pollen—or notes the lack of pollen—in honey samples sent to him by conscientious producers, private businesses and those conducting other authenticity investigations. Bryant estimates that about 60 percent of beekeepers and private entities that request their honey to be audited incorrectly estimate the plant source. In a 2011 study, Bryant found that more than 75 percent of honey sold in stores is not what bees produced as many samples tested contained no pollen at all due to over-filtration.
Once pollen is removed, there is no way to determine the origin of honey. Thus, consumers could be paying high prices for honey that has actually been imported illegally from China, is not regulated and is likely mislabeled. When melissopalynologists test for pollen in honey, they are essentially looking for the fingerprint of the food. Where did it come from?
Each honey sample tested for pollen contains 10 grams of honey diluted with water and alcohol. When diluted with water, some pollen will float regardless of centrifuge time due to air pockets and lipids. Because alcohol has a specific gravity of .7, no pollen floats. This allows the capture of all the pollen in the sample, which is then cooked in an acidic solution to remove the cytoplasm and other debris. Then, the sample is placed in a centrifuge and eventually goes under the microscope. At that time, a tracer spore is introduced to ensure observations have correct ratios, and pollen grains are identified and counted.
As a trained botanist who has practiced for more than 50 years, Bryant can identify 350,000 different types of pollen to determine the origin of honey. Samples come from around the world, from Thailand to Canada. The types and quantities of pollen spores indicate the origin of honey. For example, Manuka honey, a higher priced honey that is purported to have enhanced medicinal properties and is only cultivated from Australia and New Zealand, must have at least 2 million pollen grains per 10 grams. Sourwood honey must have 10,000 pollen grains per 10 grams of honey, and clover honey should have 60,000 to 80,000.
“I do this because I think [honey mislabeling] is a problem,” Bryant said in an interview with Laboratory Equipment. “When I do these tests with jars pulled off the shelves in different states, most don’t have pollen and those that did were incorrectly labeled. It’s like taking sandpaper and erasing your fingerprints, and I think people [should] know what they’re buying and consuming.”
But, melissopalynology is not the only method used by researchers to identify unauthentic or mislabeled honey. Some scientists, like Istvan Pelczer from Princeton University, take a molecular approach.
“There are other alternative, largely complementary methods for honey analysis,” Pelczer said in an interview with Laboratory Equipment. “Some are MS based that can identify the actual flowers from which honey is made. This is a powerful, although somewhat complicated and instrument-intensive approach.”
Pelczer, director of the NMR facility and chemistry lecturer at Princeton, co-authored a chapter in the American Chemical Society’s 2014 publication, “Science and the Law: Analytical Data in Support of Regulation in Health, Food, and the Environment.” The book chapter, titled Comprehensive Nuclear Magnetic Resonance Analysis of Honey, provides an overview of how NMR works with honey samples in their native condition without separation.
To complete this process, honey is mixed with a buffer and is transferred into a glass NMR tube. It is then moved to the magnet for measurement. Most of the time, a simple experiment is done and a one-dimensional spectrum is collected, perhaps using suppression of the possibly large water peak. The spectrum comprises many peaks distributed along the frequency/chemical shift axis. The peaks contain various intensities to reflect the relative concentration of the components and the structure of the substance.
“In an NMR study, we see the small molecule components of relatively high concentration; there are many proteins and other trace ingredients, which cannot by detected well enough by NMR,” Pelczer said. “Statistical analysis can be tailored and include the dominant sugars or focus on the rest of the spectral data.”
Pelczer cites the quantitative nature of NMR as a special advantage of the technology for the purpose of honey testing because it doesn’t require any additional exercises. Other benefits of this method include straight-forward sample preparation and non-destructive measurement.