Antimicrobial components of honey. Icon Credit: Flaticon
Interest in the antimicrobial activity of honey continues to grow. Honey is not a generic substance, and rather there is considerable variation between the taste, colour, aroma, and medicinal properties of honeys from different floral sources, regions, colonies, and apiaries. Honeys are extremely complex mixtures of up to 200 different substances and components of honey responsible for antimicrobial effects can originate from bee secretions, nectar and pollen foraged from plants, and associated microbes, and are often specific to particular varieties of honey.
High Sugar & Low pH
Honey is a supersaturated sugar solution, making it unfavourable for microbial growth. The high concentration of sugar means that water is unavailable for microbes to use and the high osmotic pressure actively draws water out of them. Honey contains over thirty organic acids including gluconic, acetic, citric, formic, lactic, and malic acids, which contribute to a low pH which generally ranges from around 3.2 and 4.5 for different honeys. This acidic pH is inhibitory to many pathogenic microbes.
Bee-Derived Compounds
Hydrogen peroxide is the main source of antimicrobial activity in most honeys. It destroys microbes by causing oxidation of their proteins and DNA. Hydrogen peroxide is produced by the enzyme glucose oxidase, which is added to honey from the salivary glands of bees during the ripening of nectar into honey. The glucose oxidase is activated when water is added, resulting in hydrogen peroxide production. The level of hydrogen peroxide depends on the floral variety of the honey, as well as its age and how it has been processed and stored.
Honey can contain several antimicrobial peptides that are part of the bee immune system and are also secreted into the honey. Bee-defensin-1, also known as royalisin, has activity against a wide range of bacterial pathogens including the bacteria responsible for European Foulbrood. Major royal jelly protein-1 is the most abundant protein in both royal jelly and honey, and breaks down into smaller antimicrobial peptides.
Plant-Derived Compounds
These encompass numerous diverse compounds and one of the most well-known ones is methylglyoxal (MGO). MGO comes from dihydroxyacetone (DHA), which is a naturally occurring phytochemical found in the nectar of flowers of certain Leptospermum species native to New Zealand and Australia (often referred to as “manuka”). MGO develops as a honey with nectar containing DHA ages, and the MGO plays a significant role in the antimicrobial activity of Leptospermum honeys.
Among other plant-derived components associated with antimicrobial activity are secondary metabolites such as polyphenols, flavonoids, volatile compounds, and alkaloids. Most of these, however, are found at concentrations that aren’t sufficient to account for significant antimicrobial activity and are thought to work in combination with other compounds in honey.
Microbiota-Derived Compounds
Microbiota means a collection of microbes; this could be all the microbes that live in the nectar taken from plants, in the bee gut, or in the honey itself. Recent studies show that honey can contain a huge variety of compounds produced by these microbes, some of which likely impact its activity. These microbes are also likely to play a significant role in the breakdown and digestion of other compounds in the honey, which could enhance or neutralise a honey’s functional properties.
Acknowledgements:
- NSW Bushfire Industry Recovery Project Website: https://www.nsw-bushfire-recovery.com/home
- Fernandes KE, Frost EA, Remnant EJ, Schell KR, Cokcetin NN and Carter DA. (2022). The role of honey in the ecology of the hive: Nutrition, detoxification, longevity, and protection against hive pathogens. Frontiers in Nutrition 9:954170. doi: 10.3389/fnut.2022.954170
- This article was peer-reviewed by Nadine Chapman and Shona Blair
