Client Citation Analysis
The Dropometer measured air/liquid surface tension by pendant drop on pure CMC and XG solutions and on zein nanoparticle dispersions in each. It did not measure rheology (Fann and Haake viscometers), particle shape (Hitachi SU8700 SEM), particle size (DLS), charge (Zetasizer zeta potential) or pH. No interfacial tension against oil was measured.
Equilibrium air/liquid surface tension in mN/m, from at least 15 pendant drops per sample, each drop left 1 to 3 min before imaging and fitted with the Young-Laplace equation.
How do polysaccharide type and concentration, and zein concentration, change the steady shear flow and surface activity of zein nanoparticles made in CMC or XG by antisolvent precipitation?
Zein nanoparticles made both thickeners far more surface active, while their effect on flow depended on the polysaccharide: CMC dispersions thickened, whereas XG dispersions mostly thinned and phase separated above 4 wt% zein.
This paper sits where food hydrocolloid rheology meets surface tension of protein nanoparticle dispersions.
Air/liquid surface tension of pure CMC and XG solutions and of zein nanoparticle dispersions in each, measured by pendant drop on the Droplet Lab tensiometer and fitted with the Young-Laplace equation. Results are plotted in Figures 11, 13, 25 and 26.
Fann and Haake coaxial cylinder viscometers gave steady shear viscosity, fitted to power law consistency (K) and flow index (n). A Hitachi SU8700 SEM imaged freeze dried particles. DLS and a Zetasizer gave exploratory size and a zeta potential of −55.8 ± 1.5 mV for one CMC dispersion. Photos showed phase separation.
Pendant drop air/liquid surface tension of all polysaccharide solutions and zein dispersions; the paper calls it a smartphone based pendant drop tensiometer supplied by Droplet Lab.
Formed the pendant drops for the Droplet Lab measurement.
Steady shear viscosity, 12 speeds from 0.9 to 600 rpm.
Steady shear viscosity, 30 speeds from 0.01 to 512 rpm.
Morphology and approximate size of zein nanoparticles in freeze dried samples.
Exploratory Z average size (about 2006 ± 80 nm, flagged by the software) and zeta potential (−55.8 ± 1.5 mV) for the 0.6 wt% CMC with zein dispersion only.
The Dropometer, which the paper describes as a smartphone based pendant drop tensiometer supplied by Droplet Lab, produced every surface tension value in the study. Drops hung from a 1.8 mm stainless steel needle on a 500 µL Hamilton gastight syringe and rested about 1 to 3 min before a smartphone image was taken.
The software fitted each drop profile with the Young-Laplace equation. The authors cite the 2017 smartphone pendant drop method paper by Chen, Amirfazli and coworkers for this approach. Each sample was measured at least 15 times on one preparation and averaged, all at room temperature.
These readings showed that pure CMC is not surface active, that pure XG lowers surface tension as it is added, and that 1 wt% zein lowers surface tension substantially in both. In the zein series at 0.5 wt% polysaccharide, surface tension fell sharply up to 1 wt% zein and then levelled off beyond 3 wt%.
The Dropometer did not measure flow behaviour, particle size, particle shape, charge or pH. The idea that zein particles crowd the surface, and the identity of the adsorbing species, are the authors' interpretations; they note that dynamic surface tension and interfacial rheology would be needed to confirm them.
The surface tension data supplied the surface activity half of the paper's conclusions and underpin its suggestion that zein dispersions could serve as plant based emulsifiers or foam stabilizers. The authors also used the polysaccharide only control values as supporting evidence that residual ethanol was negligible.
If you need to see where a protein or particle dispersion lowers surface tension, you can run the same pendant drop series in your own lab with the Dropometer.
Adding 1 wt% zein nanoparticles lowered the Dropometer surface tension of CMC and XG solutions substantially compared with the pure polysaccharides (Figures 11 and 25).
At 0.5 wt% CMC or XG, surface tension fell sharply from 0 to 1 wt% zein, then slowly, and levelled off beyond 3 wt%, which the authors link to a saturated surface (Figures 13 and 26).
Pure CMC gave a constant surface tension from 0.2 to 1 wt%, so it is not surface active, while pure XG lowered surface tension as its concentration rose.
With 1 wt% zein, surface tension rose as CMC increased, which the authors attribute to particles held in the thicker bulk. In XG it stayed flat up to 0.6 wt% and then fell.
Fann and Haake viscometers showed power law, shear thinning flow. Zein raised CMC consistency up to 4 wt% then dropped it, and lowered XG consistency, with phase separation above 4 wt% zein.
Four figures in the paper contain Dropometer surface tension data. The article is open access under a Creative Commons Attribution (CC BY) licence as stated in the paper; the version number is not printed in the text, so confirm it on the publisher page before reuse.
Compares pure CMC solutions with 1 wt% zein in CMC, all measured with the Droplet Lab pendant drop tensiometer. Credit: Li and Pal, Foods 2026, 15, 3529, CC BY (version not stated in the text).
Shows the sharp drop up to 1 wt% zein and the plateau beyond 3 wt%, from Dropometer measurements. Credit: Li and Pal, Foods 2026, 15, 3529, CC BY (version not stated in the text).
Compares pure XG solutions with 1 wt% zein in XG, all measured with the Droplet Lab pendant drop tensiometer. Credit: Li and Pal, Foods 2026, 15, 3529, CC BY (version not stated in the text).
Shows the same sharp drop and plateau beyond 3 wt% zein as the CMC series, from Dropometer measurements. Credit: Li and Pal, Foods 2026, 15, 3529, CC BY (version not stated in the text).
Food formulators want plant proteins that both thicken and stabilize interfaces. This study shows that the same zein particles can lower surface tension strongly while their effect on viscosity depends on the thickener chosen.
The authors suggest the drop in surface tension makes zein dispersions candidates for egg free mayonnaise or aerated desserts, which still needs emulsion and foam testing.
CMC and XG responded differently to zein in flow, and XG dispersions phase separated above 4 wt% zein, so surface data alone cannot pick a formulation.
Tracking surface tension against zein content showed where extra protein stops changing the surface, which can help when choosing a protein dose.
Zein lowers surface tension in both CMC and XG
Plateau beyond about 3 wt% zein
Pure CMC is not surface active; pure XG is
At 0.5 wt% polysaccharide, zein thickened CMC but thinned XG
Pure polysaccharide solutions gave the baseline that showed the zein effect and helped the authors argue that leftover ethanol was negligible.
The study let each drop rest about 1 to 3 min. Proteins keep adsorbing over time, so a fixed and reported drop age makes values comparable.
Each formulation was one preparation measured many times, which shows measurement repeatability but not batch to batch variation.
It measured air/liquid surface tension by pendant drop for pure CMC and XG solutions and for zein nanoparticle dispersions in each. Viscosity, particle size, particle shape and charge came from other instruments.
Drops hung from a 1.8 mm stainless steel needle on a 500 µL Hamilton gastight syringe and rested about 1 to 3 min. A smartphone image was fitted with the Young-Laplace equation, and at least 15 drops were averaged per sample at room temperature.
The authors attribute the plateau to a surface saturated with zein derived species. They state that the exact species (intact particles, free protein or protein and polysaccharide complexes) was not established and that dynamic surface tension would be needed.
No values are written in the text. The results appear only as plotted points in Figures 11, 13, 25 and 26, so readers should consult the figures in the open access article.
Use the formal reference below when citing the original paper.
Li, S., & Pal, R. (2026). Zein protein nanoparticles: Fabrication and rheology of their dispersions in polysaccharides. Foods, 15(19), 3529. https://doi.org/10.3390/foods15193529
Li and Pal, Foods 2026, 15, 3529. DOI: 10.3390/foods15193529