IN Brief:
- Researchers tested five UMF grades of mānuka honey against four clinically relevant respiratory bacterial pathogens.
- Whole honey inhibited bacterial growth more strongly than matched sugar controls and generally outperformed MGO-only controls.
- The in-vitro findings do not demonstrate food preservation performance but may inform future work on functional-ingredient characterisation.
Researchers at Aston University and Comvita have found that the antimicrobial activity of mānuka honey cannot be explained by sugar concentration and methylglyoxal alone, indicating that additional components in the honey matrix contribute to its measured antibacterial effect.
The peer-reviewed study was published online in Microbiology on 11 August and examined five Unique Mānuka Factor grades — UMF 5+, 10+, 12+, 15+, and 20+ — against four clinically relevant respiratory bacterial pathogens.
The organisms were methicillin-susceptible and methicillin-resistant Staphylococcus aureus, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Minimum inhibitory concentrations were established using broth microdilution assays, allowing the researchers to compare the amount of each honey needed to inhibit bacterial growth.
All five mānuka honey grades inhibited the organisms tested, with inhibitory concentrations generally decreasing as UMF grade increased. The two Staphylococcus aureus strains were the most susceptible, while higher concentrations were required against the Gram-negative bacteria.
The study then separated two factors commonly used to explain honey’s antibacterial behaviour. First, researchers prepared a control solution with a carbohydrate composition matched to honey to test whether high sugar concentration and the resulting osmotic effect could account for bacterial inhibition.
Whole mānuka honey consistently performed more strongly than the matched sugar solution. The result indicates that sugar concentration contributes to the environment experienced by the bacteria but does not account for the full antimicrobial activity measured in the experiment.
The researchers also tested solutions containing methylglyoxal, or MGO, matched to the amount present in the honey samples. MGO is widely associated with mānuka honey’s antibacterial properties and increased with the higher UMF grades assessed in the study.
Those control solutions also inhibited bacterial growth, but they were generally less potent than the corresponding whole-honey samples. The researchers concluded that MGO contributes to activity while additional constituents within the honey matrix are also involved.
For ingredient manufacturers and product developers, that result is interesting because natural materials are often bought, graded, and sold using analytical markers intended to provide a repeatable specification. A measurable compound is useful for quality control, but it can become an incomplete proxy if the desired function depends on several compounds interacting rather than on one constituent alone.
UMF grading already incorporates several measures associated with mānuka honey identity and quality. The new study does not invalidate those systems or establish a replacement specification; it narrows the scientific question around which components contribute to the antimicrobial effect observed under the test conditions.
That qualification is particularly important for a food-manufacturing audience. The research did not test mānuka honey as a preservative in a commercial food formulation, measure shelf-life extension, establish an effective inclusion level in a finished product, or evaluate sensory and processing consequences.
The work was conducted in vitro against respiratory pathogens. Performance in a laboratory broth assay cannot simply be transferred to bakery, beverage, dairy, confectionery, or other food systems, where pH, water activity, fat, protein, starch, temperature, and competing ingredients can alter antimicrobial behaviour substantially.
Processing itself could also change the compounds involved. Heating, filtration, dilution, blending, storage, and exposure to oxygen may affect individual constituents differently, so a honey retaining a specified MGO concentration after processing would not necessarily retain every other component contributing to the whole-honey effect.
That becomes relevant if future research identifies additional compounds with a meaningful role. Ingredient suppliers seeking to sell mānuka honey for a defined functional property would then need to understand how those substances vary between harvests and lots, how reliably they can be measured, and how they survive commercial handling.
Natural ingredients already present this type of quality-control problem. Agricultural origin, season, storage, processing history, and biological variability can create differences that do not occur to the same extent with a purified single compound. Manufacturers therefore need specifications that capture the characteristics actually linked to product performance rather than simply the easiest marker to analyse.
The study also illustrates the distinction between authenticity, compositional quality, and functionality. A material can meet requirements confirming that it is genuine mānuka honey while still showing variation in the exact mixture of compounds responsible for a particular biological effect.
That distinction becomes commercially important when functional claims are involved because greater analytical complexity increases the burden on suppliers and formulators. Repeatable ingredient performance requires repeatable raw materials, but biological materials rarely reduce neatly to one number.
The researchers’ next scientific task is to identify which additional constituents explain the difference between MGO controls and whole honey. Existing work has suggested that phenolic compounds and other molecules may interact with methylglyoxal, but the present study does not establish one definitive additional component responsible for the observed activity.
Nor should the findings be stretched into a claim that higher-grade mānuka honey will control pathogens in food. Demonstrating that would require application-specific formulation studies, challenge testing, processing validation, shelf-life work, and consideration of the regulatory position for any proposed antimicrobial use.
The immediate finding is narrower and more useful: five mānuka honey grades displayed UMF-dependent antimicrobial activity in the tested system, and neither matched sugar nor MGO alone reproduced the effect of the whole material.
For food scientists, the next question is therefore not whether mānuka honey contains methylglyoxal — that is already well established — but how much of its measurable function depends on the rest of the matrix and whether that complexity can eventually be translated into a specification robust enough for controlled manufacturing applications.
