A clove powder can leave the dryer with a low water-activity reading and still take up moisture during humid exposure. A laboratory study of freeze-dried clove extract makes that distinction unusually clear: the six carrier formulations did not differ significantly in initial water activity, but their measured hygroscopicity did.[1] For a buyer selecting an encapsulated powder, that is a reason to ask what happened after exposure—not simply which sample started driest.
The useful question is not whether gum arabic or maltodextrin is the better carrier in general. It is which combination meets the handling and composition requirements of the particular ingredient. The research supports a focused comparison, not a commercial shelf-life promise.
What the clove experiment actually compared
The researchers extracted clove buds with 80% methanol, concentrated the extract and freeze-dried it before encapsulation.[1] They prepared six wall-material blends of maltodextrin (MD, dextrose equivalent 16.5–19.5) and gum arabic (GA), mixed freeze-dried extract with a 30% w/v wall-material solution at a stated ratio of 1:4, homogenized the mixtures, froze them at −80 °C and freeze-dried them for about 72 hours.[1] The MD:GA labels describe the carrier blend, not the composition of undiluted clove extract. The method does not specify the basis of the 1:4 ratio; it should not be read as a verified dry extract-to-carrier mass ratio.[1]
These were laboratory freeze-dried extract powders—not ground cloves, distilled clove oil or a demonstrated commercial spray-dried ingredient.[1] The methanolic extraction route also means the experiment should not be treated as a ready-to-use food-production specification.
For initial water activity, the researchers used an analyzer at 25 °C.[1] For hygroscopicity, they exposed 1 g of powder to a saturated sodium chloride environment at 75.3% relative humidity and weighed it after seven days.[1] The latter method describes humid exposure, not testing of a sealed retail pouch. It does not state an exposure temperature or give an explicit calculation equation for the reported hygroscopicity percentage.[1]
Similar initial readings, different humid-exposure results
The table below reproduces the water-activity and hygroscopicity columns from the original paper’s Table 2. Values are means ± standard deviations; the study reports three separate experimental runs.[1]
| Carrier blend, MD:GA | Initial water activity | Reported hygroscopicity, % |
|---|---|---|
| Carrier blend, MD:GA0:100 | Initial water activity0.29 ± 0.02 | Reported hygroscopicity, %10.1 ± 0.40 a |
| Carrier blend, MD:GA50:50 | Initial water activity0.26 ± 0.03 | Reported hygroscopicity, %9.10 ± 0.26 a |
| Carrier blend, MD:GA62.5:37.5 | Initial water activity0.24 ± 0.03 | Reported hygroscopicity, %7.17 ± 0.36 b |
| Carrier blend, MD:GA75:25 | Initial water activity0.23 ± 0.01 | Reported hygroscopicity, %6.67 ± 0.47 b |
| Carrier blend, MD:GA87.5:12.5 | Initial water activity0.28 ± 0.02 | Reported hygroscopicity, %6.74 ± 0.45 b |
| Carrier blend, MD:GA100:0 | Initial water activity0.28 ± 0.03 | Reported hygroscopicity, %6.70 ± 0.36 b |
The overall formulation comparison was nonsignificant for water activity (p = 0.17), but significant for hygroscopicity (p < 0.01).[1] In the hygroscopicity column, different letters denote differences under the authors’ Tukey test; the four MD-rich formulations share the letter b.[1] Thus, 75:25 had the lowest numerical hygroscopicity, but the study does not establish it as significantly better than 62.5:37.5, 87.5:12.5 or all-MD on that measure. Nor does the nonsignificant water-activity result establish formal equivalence.
This is the practical distinction: an initial reading did not identify the same differences as the seven-day exposure test. It does not follow that every increase in MD provides a meaningful improvement, or that the lowest numerical result identifies the best commercial formulation.
There are reporting inconsistencies worth retaining rather than smoothing over. Table 2 gives all-MD moisture as 1.39% and solubility as 93.3%, whereas the discussion gives 1.30% and 95%; the all-GA solubility of 89.9% also conflicts with the abstract’s blanket “>90%” description.[1] Those disputed moisture and solubility values are not used in the comparison above.
A lower uptake result does not answer the aroma question
If the purchasing objective includes clove aroma, ask for a relevant chemical result and an application sensory assessment separately. The clove study measured eugenol by HPLC and phenolics by chemical assays; those endpoints are not a sensory-panel measurement of aroma retention.[1] Its Table 4 gives eugenol loading efficiencies of 70.5–75.6%, with no significant formulation effect reported (p = 0.78).[1] Here, loading efficiency compares the measured eugenol concentration after drying with the theoretical concentration before drying; it is not the eugenol mass fraction of the powder.[1] That does not support declaring the lowest-uptake blend the best eugenol-retaining blend.
An independent spray-drying experiment offers another useful caution. It used 99%-purity eugenol—not whole clove extract—with a fixed MD:GA blend of 3:1 and added soy lecithin, while varying processing conditions and the eugenol-to-polymer ratio across 32 experiments.[3] Its Table 3 reports 96.07% eugenol encapsulation efficiency but only 33.72% product recovery for DF16; DF06 instead gave 47.37% efficiency and 65.35% recovery.[3] A high result on one endpoint did not identify the best overall manufacturing outcome.
The two papers also use “encapsulation efficiency” differently. The clove paper calculates (total core phenolics − surface phenolics) / total core phenolics × 100; the eugenol paper compares experimental with theoretical eugenol content.[1][3] Their percentages should not appear together in a carrier-performance ranking. The independent study helps separate processing yield from compound loading; it does not replicate the clove humidity experiment or establish sensory retention.
Why the carrier name alone is not a moisture specification
A separate study of spray-dried elderberry pomace extract illustrates the transfer problem. Its all-MD formulation had a reported moisture content of 5.63 ± 0.15%, compared with 4.10 ± 0.09% for all-GA—the reverse of the endpoint ordering in the freeze-dried clove study.[2][1] The elderberry experiment used a different extract and spray drying at an inlet temperature of 120 ± 1 °C.[2] Its methods contain an unresolved ratio discrepancy: the drying section states 1:2 carrier:extract dry mass, while the assay section uses 1:6 extract:carrier to calculate expected compound concentration.[2] The moisture results are cited as reported; neither ratio is used here to calculate a carrier fraction or normalize performance.
This is not evidence that GA reverses its inherent behavior, or that one drying method caused the difference: several features changed between experiments. It is evidence against transferring a finished-powder moisture ranking solely from the carrier names. The elderberry moisture results are also not a replication of seven-day humidity uptake.
Turn the finding into a material-selection decision
For a clove powder intended for repeated opening and dispensing, the useful next comparison is between representative candidate powders under an agreed exposure protocol. Request carrier identities and proportions, drying route, initial water activity, and measured uptake under stated humidity, temperature and duration. If flow or caking matters to the application, include those outcomes rather than assuming an uptake percentage predicts them. These are proposed qualification steps, not tests already demonstrated for a supplier’s material.
For an aroma-led application, add eugenol content and a sensory comparison in the intended formulation. For a sealed-pack project, test the actual powder–package combination against agreed end-of-life criteria. The clove paper separately tested storage in screw-capped tubes at 4 or 25 °C for 40 days and in sealed tubes at 60 °C for seven days.[1] Neither those storage tests nor the seven-day humidity exposure establish a pouch barrier requirement, a desiccant dose or a shelf life.[1]
The defensible conclusion is narrower—and more useful—than “low water activity means stable.” In this clove experiment, carrier selection changed the reported humidity uptake without producing a significant initial water-activity difference.[1] Use that result to choose the next comparison, not to substitute for package, aroma or finished-product validation.
Related measurement guide
Water content vs loss on drying: methods and reporting basis addresses analytical measurement, not moisture uptake after humid exposure.
Sources
[1] Clove freeze-dried GA/MD primary study: original JATS
[2] Elderberry pomace spray-drying primary study: original JATS
[3] Natural-polymer spray-dried eugenol primary study: original JATS