Using honey DNA to detect counterfeits

By Heiloi Yip

Honey needs no introduction as a versatile food product that you or I may use in our everyday lives, from being dissolved in tea or lightly drizzled on some pancakes. Not only is honey a nutrient- and energy-rich substance, but it also has antibacterial properties and various health benefits. For example, honey can act as a disinfectant and promote the healing of wounds and ulcers.1 However, this benign reputation of honey is threatened by widespread honey adulteration, wherein authentic honey is diluted with other products before being bottled for sale. Despite rapid growth in the market for honey, currently there is limited legislation regulating the sale of honey, which allows adulteration to occur unchecked. In order to classify authentic and adulterated honey, we need methods of detecting signs of adulteration within honey samples.

To understand why adulteration is a problem and how it can be detected, let’s first review the process of honey production. Honey starts off as nectar found in flowers. Honeybees forage around their hive for surrounding flowers, seeking to harvest the nectar within the flowers. Back in the hive, the bees convert the nectar to honey before storing it within the hive. Nectar of different plants can have different properties (e.g. colour, sweetness), and this variety is reflected in the honey that can be produced from said nectar. Most importantly, since honeybees can only travel a limited distance from the hive, a specific array of flowers would be foraged. As a result, the honey produced at a given hive has properties that are highly specific to the hive’s location. This will be important later for determining the origins of a bottle of honey.

There are many reasons why honey is adulterated. The obvious reason is to acquire a product that is cheaper to manufacture than pure honey, thus letting bottles be priced cheaper than authentic honey of an identical volume. This has clear consequences on the honey being sold, as the beneficial properties are now diluted. Some evidence suggests that adulteration can even increase the chances of harmful side-effects, such as diabetes from added sugar.2 The consumers, on the other hand, are typically oblivious to this scandal, as the adulterated honey is allowed to be sold as the healthy product it is meant to imitate. The most common form of adultery is to dilute the honey with non-honey products, such as sugar or corn syrup. Fortunately, these forms of adultery can be detected relatively easily through a variety of assays, from chromatography to spectroscopy.3

However, there exists a more subtle type of honey adulteration: mixing honey from a single source with another honey. This form of adulteration is especially prevalent with Manuka honey, a highly valuable type of honey from New Zealand. The valuable honey is often adulterated with more readily available types of honey to produce bottles that undercut the prices of authentic Manuka honey. While not as obviously problematic as mixing with non-honey products, this type of adulteration is not as easy to detect. That would require the ability to discriminate the origins of where the honey was harvested.2 Pollen microscopy has been traditionally used to assess the origins of a bottle of honey, by looking at plant pollen within the honey that have been carried from the foraged plants. The pollens represent the types of plants where the nectar was collected from, painting a story of how and where the honey was made. However, not only is this process time consuming and labour intensive, but it cannot be used to analyze filtered honeys, which are pollen-free.4

With thanks to modern advances in bioinformatics, we now have more powerful ways of tracing a honey’s origin. Since honey is mostly composed of the foraged plants’ matter (e.g. pollen and nectar), one can analyze the DNA from said plant matter and treat it as a barcode for the honey’s origins. By isolating and sequencing genomic DNA from a sample of honey, and utilizing a database of plant genomes, a search can be conducted to identify the plant constituents of the honey down to the species level. Based on what plants were identified and the species’ natural range, the honey’s location of origin can be accurately identified.4 This method can be modified to look at a wider variety of barcodes, such as including searches for the genomes of bacteria and fungi, or by looking for plant-specific peptide markers.5

Similar studies have been conducted analyzing honey and flora from various parts of world, ranging from Europe to south Asia.4,6 Honey barcoding, while promising for unveiling adultery, is still a nascent field that will gain traction as more data is collected. Meanwhile, the current lack of legislation on honey means that adulterated honey will continue being sold in most stores and supermarkets. If you are concerned about getting authentic honey, you can instead get honey from farmers’ markets to support locally and genuinely produced honey.

References:

1. Al-Waili N, Salom K, Al-Ghamdi AA. Honey for Wound Healing, Ulcers, and Burns; Data Supporting Its Use in Clinical Practice. The Scientific World JOURNAL. 2011;11:766–87.

2. Fakhlaei R, Selamat J, Khatib A, Razis AFA, Sukor R, Ahmad S, et al. The Toxic Impact of Honey Adulteration: A Review. Foods. 2020 Oct 26;9(11):1538.

3. Peng J, Xie W, Jiang J, Zhao Z, Zhou F, Liu F. Fast Quantification of Honey Adulteration with Laser-Induced Breakdown Spectroscopy and Chemometric Methods. Foods. 2020 Mar;9(3):341.

4. Wirta H, Abrego N, Miller K, Roslin T, Vesterinen E. DNA traces the origin of honey by identifying plants, bacteria and fungi. Sci Rep. 2021 Feb 26;11:4798.

5. Bong J, Middleditch M, Loomes KM, Stephens JM. Proteomic analysis of honey. Identification of unique peptide markers for authentication of NZ mānuka (Leptospermum scoparium) honey. Food Chemistry. 2021 Jul 15;350:128442.

6. Saravanan M, Mohanapriya G, Laha R, Sathishkumar R. DNA barcoding detects floral origin of Indian honey samples. Genome. 2019 May 1;62(5):341–8.

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