REVIEW 3 major objections 3 minor 52 references
Hierarchical Plant Protein Microcapsules for Hydrophilic and Hydrophobic Cargo Molecules
T0 review · 3 major / 3 minor · reviewed 2026-08-11 · deepseek-v4-flash
Pith's one-line read Plant protein microcapsules made by tandem emulsification can carry both hydrophilic and hydrophobic cargo, retain it for a month, release it under digestive enzymes, and are claimed to biodegrade at 98% relative to cellulose.
desk verdict The encapsulation work is real, but the 'meets ISO 14851' claim is a misreading of the standard, and the paper needs major revision before it can be taken seriously. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The central object is a hierarchical microcapsule produced by tandem emulsification: two flow-focusing PDMS chips, one hydrophilically treated and one hydrophobically silanized, connected in series to make a triple water-in-oil-in-water-in-oil (W/O/W/O) emulsion. The protein shell forms because sonication and heating in 42% aqueous acetic acid unfold soy or pea protein isolates into oligopeptides that reassemble into beta-sheet-rich fibrils, a hydrogel network; CaCl2 then drives Ca2+-mediated cross-linking and electrostatic shielding, balancing osmotic pressure so the capsules neither swell nor leak. This machinery is what enables simultaneous hydrophilic and hydrophobic cargo encapsulation and the controlled release behaviour.
What would settle it
An independent ISO 14851 test that reports absolute biodegradation values rather than values relative to cellulose would settle the claim: if the capsules' absolute biodegradation is below 90%, the paper's statement that they meet the ISO 14851 threshold fails under the interpretation it invokes.
Extended reading notes
Core claim
The central claim is that hierarchical microcapsules assembled from pea or soy protein isolates can solve the dual problem of animal-based or synthetic microcapsules. Using a two-chip tandem emulsification system, the authors form water-in-oil-in-water-in-oil emulsions in which plant protein dissolved in aqueous acetic acid by sonication and heating self-assembles into beta-sheet fibrillar hydrogels. Washing with CaCl2 balances osmotic pressure, keeping the shells intact and retaining hydrophilic model cargo (fluorescein) for at least one month while also encapsulating hydrophobic ingredients such as fragrances, vitamin E, and essential oils. The paper further reports that the microcapsules are as digestible as pure pea protein, release riboflavin when exposed to simulated gastric fluid, protect encapsulated iron from polyphenol-driven oxidation, and show relative biodegradability of 98.0% compared to cellulose, which the authors interpret as satisfying the 90% biodegradability requirement they attribute to ISO 14851 for microplastics in freshwater.
Load-bearing premise
The load-bearing premise is that the ISO 14851 freshwater biodegradability test sets a 90% pass threshold and that a 98% result measured relative to cellulose satisfies it; the paper's own absolute degradation numbers (87.5% for oxygen demand, 82.4% for CO2) are below that threshold.
Editorial extensions
If this is right
- Because measured digestibility is comparable to pure pea protein, the capsules could be used as an ingestible carrier in food and beverage products.
- Because simulated gastric fluid triggers release in a two-stage in vitro digestion, the capsules could enable controlled delivery of nutraceutical or pharmaceutical actives.
- Because encapsulated iron is protected from polyphenol-driven oxidation for two weeks, the capsules could support iron fortification of staple foods without color or taste degradation.
- Because relative biodegradation is reported as 98.0% against cellulose, the paper argues the capsules meet the ISO 14851 freshwater microplastic biodegradability threshold and could replace synthetic polymer microcapsules.
- Because CaCl2 in the internal phase prevents leakage for at least one month in the fluorescein model, osmotic balance is presented as the key control for shelf-life.
Reading between the lines
- My inference: the ISO 14851 compliance claim is an interpretation, not a direct measurement—ISO 14851 is fundamentally a test method for biochemical oxygen demand, and the paper's own absolute values (87.5% O2, 82.4% CO2) fall below the 90% figure, so the 'meets the standard' conclusion depends on accepting relative-to-cellulose comparison.
- My inference: the one-month retention and enzyme-triggered release are demonstrated quantitatively for fluorescein and riboflavin; extending those guarantees to every listed vitamin, essential oil, and iron would require cargo-by-cargo measurements.
- My inference: replacing microplastics in consumer products would require the tandem-emulsification process to be scaled beyond laboratory throughput and the capsules to survive drying, sterilization, and formulation conditions found in real products.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript reports a droplet-microfluidic tandem-emulsification method for fabricating plant-protein (soy/pea) microcapsules that can encapsulate both hydrophilic and hydrophobic cargo. The authors demonstrate osmotic-pressure balancing with CaCl2, cargo retention over one month, digestive-enzyme-triggered release, prevention of iron oxidation in a food matrix, and digestibility comparable to pure pea protein. They further report a relative biodegradability of 98.0% versus cellulose and claim that this fulfills a 90% biodegradability requirement stipulated by ISO 14851 for freshwater microplastics.
Significance. If the encapsulation results hold, the paper offers a useful advance for food, nutraceutical, and personal-care applications: the tandem-emulsification scheme is versatile, the CaCl2 osmotic-balancing strategy is directly demonstrated with retention data, the iron-stabilization experiments are well controlled, and the digestibility comparison provides practical context. The manuscript also benefits from direct measurements against external references (cellulose for biodegradability, pea protein for digestibility). However, the central environmental claim of ISO 14851 compliance is not supported by the data or by the standard, and the paper contains an internal contradiction about the stability of sonicated versus vortexed primary emulsions. These issues must be resolved before the paper can be considered for publication.
major comments (3)
- [Abstract; Results and Discussion, 'Biodegradability of plant protein microcapsules'] The claim that the microcapsules 'fulfill the biodegradability standards stipulated by ISO 14851 ... (90%)' is not supported. ISO 14851 is an aqueous aerobic biodegradability test method based on oxygen demand; it does not define a 90% pass/fail threshold. The paper's own absolute biodegradation values are 82.4% (CO2 basis) and 87.5% (O2 basis), both below 90%. The 98.0% figure is a relative value calculated against the cellulose reference, and relative-to-reference ratios are not a criterion in ISO 14851. The abstract and conclusion should be revised to state the measured absolute values and to avoid claiming compliance with a nonexistent ISO threshold; if compliance with a 90% standard is intended, the authors must cite the specific regulation and show the microcapsules meet that absolute threshold.
- [Results and Discussion, Fig. 3G and Fig. S2] The text contains a direct contradiction about sonication versus vortexing. It states that sonication 'is another effective strategy to enhance emulsion stability and can be used to fabricate smaller emulsions than that achieved just by vortexing,' but then states that 'when the primary emulsion is generated using vortexing rather than sonication, the emulsion is more stable (Fig. 3G).' These statements cannot both be true as written. Since the Methods section specifies sonication for preparing primary emulsions, the manuscript must clarify which preparation method is actually used and which stability claim is supported by data.
- [Tables S1 and S2; Biodegradability of plant protein microcapsules] The relative biodegradation values on the O2 and CO2 bases are inconsistent: Table S1 gives 106.1% relative biodegradation for O2, while Table S2 gives 98.0% for CO2. The manuscript reports only the 98.0% value without acknowledging that the O2-based calculation exceeds 100% relative to cellulose. This selective reporting further weakens the biodegradability claim; the authors should present both values and explain the discrepancy, or justify why only the CO2-based value is used.
minor comments (3)
- [Fig. 1 and Materials and Methods, 'Microcapsule fabrication'] The pressure settings are inconsistent: Fig. 1 states '200/250/400 Pa,' while the Methods section states 'inner phase, 200 mbar; middle phase, 400 mbar; outer phase, 200 mbar.' The units and values should be unified, as the flow conditions are critical for reproducing the tandem-emulsification process.
- [Results and Discussion, CaCl2 optimization] The statement that 'the CaCl2 concentration was optimized at 0.5 M' is not fully supported by the data shown; the text and Fig. 4 mention increased gel hardness with 0.5 M CaCl2, but no concentration-dependence curve is provided. Adding a dose–response measurement would strengthen this optimization claim.
- [Materials and Methods, 'Digestibility of plant protein microcapsules'] The Boisen digestibility values are reported as percentages exceeding 100% (100.8% and 99.7%). The authors should clarify whether these are relative to a protein standard or are corrected values, and if necessary provide the calculation basis to avoid confusion.
Circularity Check
One load-bearing self-citation supports the ISO 14851 biodegradability claim; the core encapsulation, release, and digestibility results are direct measurements and are not circular.
-
self citation load bearing
[Abstract; Results and Discussion (biodegradability paragraph); Materials and Methods, 'Biodegradability of plant protein microcapsules'; reference 41]
"the microcapsules met the biodegradability requirement mandated by the International Organization for Standardization (ISO 14851) for microplastics in freshwater conditions (90%) (41). ... The relative biodegradation of the tested microcapsule was 98.0% compared with cellulose, exceeding the ISO 14851 standard for biodegradability (90%)."
The 90% threshold is the load-bearing premise that converts the measured relative biodegradation (98.0% vs cellulose) into the conclusion that an ISO standard is fulfilled. The only authority cited for this threshold is reference 41, an EP patent application by the same authors, not the ISO 14851 standard itself. The absolute measurements in Tables S1 and S2 (87.5% on an O2 basis, 82.4% on a CO2 basis for the microcapsules) are external data, but the 90% pass/fail criterion is imported from the authors' own patent. Without that self-citation, the 'fulfilling ISO 14851' conclusion does not follow from the reported data, so the central environmental claim is supported by a self-citation rather than by the independent standard it invokes.
full rationale
The main experimental narrative is self-contained: the paper directly demonstrates microcapsule formation by tandem emulsification, cargo retention with CaCl2, enzyme-triggered release, iron stabilization, and digestibility versus pea protein. These results are measurements against external benchmarks and do not derive predicted outcomes from fitted parameters or from equations that reduce to definitions. The relative biodegradability value is a ratio of measured values (microcapsule vs cellulose), so it is not circular by construction. The one significant circularity-adjacent step is the ISO 14851 claim: the paper repeatedly asserts that 98.0% relative biodegradation meets a 90% ISO requirement, but the cited support for that requirement is the authors' own patent application (ref 41), not the ISO standard. This makes the environmental headline claim load-bearing on a self-citation. Because the rest of the paper's central claims retain independent experimental content, the score is moderate rather than high.
Assumptions & free parameters
free parameters (3)
- CaCl2 concentration =
0.5 M
- Protein concentration and solvent =
10% w/v protein in 42% v/v aqueous acetic acid
- Microfluidic pressure settings =
200/400/200 mbar (also reported as 200/250/400 Pa)
assumptions (4)
- domain assumption Plant proteins can be dissolved in aqueous acetic acid and self-assemble into beta-sheet-rich fibrillar hydrogels upon cooling
- domain assumption Tandem flow-focusing emulsification produces stable W/O/W/O emulsions with tunable droplet sizes
- domain assumption The Boisen in vitro digestibility assay predicts in vivo protein digestibility
- ad hoc to paper ISO 14851 specifies a 90% biodegradability pass/fail threshold and relative biodegradation compared with cellulose is the criterion
Cite this review
Pith. "Pith review of Hierarchical Plant Protein Microcapsules for Hydrophilic and Hydrophobic Cargo Molecules." pith.science (2026). https://pith.science/paper/MBFE5CAZ
@misc{pith2026250101962,
author = {Pith},
title = {Pith review of: Hierarchical Plant Protein Microcapsules for Hydrophilic and Hydrophobic Cargo Molecules},
year = {2026},
howpublished = {\url{https://pith.science/paper/MBFE5CAZ}},
note = {Machine review of arXiv:2501.01962}
}
read the original abstract
Microscale hydrogels comprised of macromolecular networks have increasingly been used for applications involving cell encapsulation, tissue engineering and for the storage and release of active cargo molecules. However, the majority of such microgels are formed from nonbiodegradable synthetic polymers, involving harmful solvents, or using animal proteins, such as silk and gelatin, which can have a negative environmental impact and lack sustainability. Furthermore, most encapsulation techniques involve either protecting hydrophobic or hydrophilic cargo, but rarely both. In order to address these issues, we employed droplet-microfluidics to develop novel, plant protein microcapsules capable of containing both hydrophilic and hydrophobic cargo molecules. The microcapsule structure and cargo release rates were controlled by balancing osmotic pressures between the outer and inner phases of the capsules. Moreover, the digestibility of the microcapsules was comparable with that of pure pea protein, thereby enabling the use of these microcapsules for food and beverage applications. In addition, digestive enzymes can trigger the release of the encapsulated active ingredients, and hence, these microcapsules are well suited for the controlled delivery of active nutraceutical or pharmaceutical ingredients. Finally, we investigated the biodegradability of the microcapsules. It was determined that the plant protein microcapsules exhibited 98.0% biodegradability (as compared with cellulose), thereby fulfilling the biodegradability standards stipulated by the International Organization for Standardization (ISO 14851) for microplastics in freshwater conditions (90%). Hence, the plant protein microcapsules can have numerous applications in the food, nutraceutical, pharmaceutical, cosmetic, personal care, and agriculture industries.
Reference graph
Works this paper leans on
-
[1]
J. Siepmann, F. Siepmann, Modeling of diffusion controlled drug delivery. Journal of controlled release 161, 351-362 (2012)
work page 2012
-
[2]
N.-D. Dinh et al. , Functional reservoir microcapsules generated via microfluid ic fabrication for long-term cardiovascular therapeutics. Lab on a Chip 20, 2756 -2764 (2020)
work page 2020
-
[3]
H. Tan et al., Heterogeneous multi-compartmental hydrogel particles as synthetic cells for incompatible tandem reactions. Nature communications 8, 1-10 (2017)
work page 2017
-
[4]
N. D. Dinh et al., Effective light directed assembly of building blocks with microscale control. Small 13, 1700684 (2017)
work page 2017
-
[5]
Liang et al., Upconversion amplification through dielectric superlensing modulatio n
L. Liang et al., Upconversion amplification through dielectric superlensing modulatio n. Nature communications 10, 1-9 (2019)
work page 2019
-
[6]
Leslie, Review of microplastics in cosmetics
H. Leslie, Review of microplastics in cosmetics. IVM Institute for Environmental Studies 476, 1-33 (2014)
work page 2014
-
[7]
S. M. Bashir, S. Kimiko, C. -W. Mak, J. K.-H. Fang, D. Gonçalves, Personal care and cosmetic products as a potential source of environmental contamination by microplastics in a densely populated Asian City. Frontiers in Marine Science 8, 604 (2021)
work page 2021
-
[8]
C. F. Hunt, W. H. Lin, N. Voulvoulis, Evaluating alternatives to plastic microbeads in cosmetics. Nature Sustainability 4, 366-372 (2021)
work page 2021
Show all 52 references
-
[9]
https://www.eea.europa.eu/publications/microplastics-from-textiles-towards-a (
-
[10]
A. D. Vethaak, J. Legler, Microplastics and human health. Science 371, 672 -674 (2021)
2021
-
[11]
Kentin, H
E. Kentin, H. Kaarto, An EU ban on microplastics in cosmetic products and the right to regulate. Review of European, Comparative & International Environmental Law 27, 254-266 (2018)
2018
-
[12]
Guerranti, T
C. Guerranti, T. Martellini, G. Perra, C. Scopetani, A. Cincinelli, Microplastics in cosmetics: Environmental issues and needs for global bans. Environmental toxicology and pharmacology 68, 75-79 (2019)
2019
-
[13]
T. Y. Lee et al., Microfluidic production of biodegradable microcapsules for sustained release of hydrophilic actives. Small 13, 1700646 (2017)
2017
-
[14]
R. P. Seekell et al., Oxygen delivery using engineered microparticles. Proceedings of the National Academy of Sciences 113, 12380-12385 (2016)
2016
-
[15]
Elia et al., Encapsulation of volatile compounds in silk microparticles
R. Elia et al., Encapsulation of volatile compounds in silk microparticles. Journal of coatings technology and research 12, 793-799 (2015)
2015
-
[16]
Shchepelina, I
O. Shchepelina, I. Drachuk, M. K. Gupta, J. Lin, V. V. Tsukruk, Silk‐on‐silk layer ‐by‐ layer microcapsules. Advanced Materials 23, 4655-4660 (2011)
2011
-
[17]
K. D. Hermanson, D. Huemmerich, T. Scheibel, A. R. Bausch, Engineered microcapsules fabricated from reconstituted spider silk. Advanced Materials 19, 1810- 1815 (2007)
2007
-
[18]
Sakai et al
S. Sakai et al. , C ell-enclosing gelatin -based microcapsule production for tissue engineering using a microfluidic flow -focusing system. Biomicrofluidics 5, 013402 (2011)
2011
-
[19]
Ye et al
X. Ye et al. , Protein/protein nanocomposite based on whey protein nanofibrils in a whey protein matrix. ACS Sustainable Chemistry & Engineering 6, 5462-5469 (2018)
2018
-
[20]
Hayasaka (2014) Method for manufacturing multicore gelatin microcapsule
H. Hayasaka (2014) Method for manufacturing multicore gelatin microcapsule. (Google Patents)
2014
-
[21]
Ju et al., Biodegradable chito-beads replacing non -biodegradable microplastics for cosmetics
S. Ju et al., Biodegradable chito-beads replacing non -biodegradable microplastics for cosmetics. Green Chemistry 23, 6953-6965 (2021)
2021
-
[22]
M. R. GARCIA, T. Knowles, A. Levin, A. Kamada (2020) Plant based functio nal materials. (Google Patents)
2020
-
[23]
Ammala, Biodegradable polymers as encapsulation materials for cosmetics and personal care markets
A. Ammala, Biodegradable polymers as encapsulation materials for cosmetics and personal care markets. International journal of cosmetic science 35, 113-124 (2013)
2013
-
[24]
I. T. Carvalho, B. N. Estevinho, L. Santos, Application of microencapsulated essential oils in cosmetic and personal healthcare products –a review. International journal of cosmetic science 38, 109-119 (2016)
2016
-
[25]
Nesterenko, I
A. Nesterenko, I. Alric, F. Silvestre, V. Durrieu, Vegetable proteins in microencapsulation: A review of recent interventions and their effectiveness. Industrial crops and products 42, 469-479 (2013)
2013
-
[26]
Kamada et al., Controlled self-assembly of plant proteins into high -performance multifunctional nanostructured films
A. Kamada et al., Controlled self-assembly of plant proteins into high -performance multifunctional nanostructured films. Nature communications 12, 1-10 (2021)
2021
-
[27]
K. Seo, D. Kim, S. Sanchez, Fabrication and applications of complex -shaped microparticles via microfluidics. Lab on a Chip 15, 3622-3626 (2015)
2015
-
[28]
Dendukuri, P
D. Dendukuri, P. S. Doyle, The synthesis and assembly of polymeric microparticles using microfluidics. Advanced Materials 21, 4071-4086 (2009)
2009
-
[29]
Yeh et al
J. Yeh et al. , Micromolding of shape -controlled, harvestable cell -laden hydrogels. Biomaterials 27, 5391-5398 (2006)
2006
-
[30]
T. Y. Lee, T. M. Choi, T. S. Shim, R. A. Frijns, S.-H. Kim, Microfluidic production of multiple emulsions and functional microcapsules. Lab on a Chip 16, 3415-3440 (2016)
2016
-
[31]
van Zee et al., High-throughput selection of cells based on accumulated growth and division using PicoShell particles
M. van Zee et al., High-throughput selection of cells based on accumulated growth and division using PicoShell particles. Proceedings of the National Academy of Sciences 119, e2109430119 (2022)
2022
-
[32]
Li et al
W. Li et al. , Microfluidic fabrication of microparticles for biomedical applicatio ns. Chemical Society Reviews 47, 5646-5683 (2018)
2018
-
[33]
Polenz, S
I. Polenz, S. S. Datta, D. A. Weitz, Controlling the morphology of polyurea microcapsules using microfluidics. Langmuir 30, 13405-13410 (2014)
2014
-
[34]
Lee et al
H. Lee et al. , Encapsulation and enhanced retention o f fragrance in polymer microcapsules. ACS applied materials & interfaces 8, 4007-4013 (2016)
2016
-
[35]
Nomura, A
T. Nomura, A. F. Routh, Benign preparation of aqueous core poly lactic -co-glyco lic acid (PLGA) microcapsules. Journal of colloid and interface science 513, 1-9 (2018)
2018
-
[36]
Shimanovich et al., Protein microgels from amyloid fibril networks
U. Shimanovich et al., Protein microgels from amyloid fibril networks. ACS nano 9, 43-51 (2015)
2015
-
[37]
Shimanovich et al
U. Shimanovich et al. , Silk micrococoons for protein stabilisation and molecular encapsulation. Nature communications 8, 1-9 (2017)
2017
-
[38]
Xu et al., Deformable and Robust Core–Shell Protein Microcapsules Templated by Liquid–Liquid Phase ‐Separated Microdroplets
Y. Xu et al., Deformable and Robust Core–Shell Protein Microcapsules Templated by Liquid–Liquid Phase ‐Separated Microdroplets. Advanced Materials Interfaces 8, 2101071 (2021)
2021
-
[39]
Alessandri et al., Cellular capsules as a tool for multicellular spheroid p roduction and for investigating the mechanics of tumor progression in vitro
K. Alessandri et al., Cellular capsules as a tool for multicellular spheroid p roduction and for investigating the mechanics of tumor progression in vitro. Proceedings of the National Academy of Sciences 110, 14843-14848 (2013)
2013
-
[40]
Kim et al
J.-W. Kim et al. , Recent Advances in Microfluidic Production of Functional Microcapsules by Multiple-Emulsion Templating. Lab on a Chip (2022)
2022
-
[41]
M. R.-G. a. T. Knowles (2022) Plant-Based Microcapsules. ed A1 (EP)
2022
-
[42]
R. M. Erb, D. Obrist, P. W. Chen, J. Studer, A. R. Studart, Predicting sizes of droplets made by microfluidic flow-induced dripping. Soft Matter 7, 8757-8761 (2011)
2011
-
[43]
Guldiken, J
B. Guldiken, J. Stobbs, M. Nickerson, Heat induced gelation of pulse protein networks. Food Chemistry 350, 129158 (2021)
2021
-
[44]
L. Lin, H. Oh, H. Deeth, M. Wong, The effects of casein and whey proteins on the rheological properties of calcium-induced skim milk gels. International Dairy Journal 113, 104893 (2021)
2021
-
[45]
Habeych, V
E. Habeych, V. van Kogelenberg, L. Sagalowicz, M. Michel, N. Galaffu, Strategies to limit colour changes when fortifying food products with iron. Food Research International 88, 122-128 (2016)
2016
-
[46]
A. C. Anselmo et al. , A heat -stable microparticle platform for oral micronutrient delivery. Science translational medicine 11, eaaw3680 (2019)
2019
-
[47]
D. C. Duffy, J. C. McDonald, O. J. Schueller, G. M. Whitesides, Rapid prototyping of microfluidic systems in poly (dimethylsiloxane). Analytical chemistry 70, 4974-4984 (1998)
1998
-
[48]
Dinh et al., Microfluidic construction of minimalistic neuronal co -cultures
N.-D. Dinh et al., Microfluidic construction of minimalistic neuronal co -cultures. Lab on a Chip 13, 1402-1412 (2013)
2013
-
[49]
Dinh et al., Preparation of neuronal co -cultures with single cell precision
N.-D. Dinh et al., Preparation of neuronal co -cultures with single cell precision. JoVE (Journal of Visualized Experiments), e51389 (2014)
2014
-
[50]
Eggersdorfer et al
M. Eggersdorfer et al. , Tandem emulsifi cation for high -throughput production of double emulsions. Lab on a Chip 17, 936-942 (2017)
2017
-
[51]
Shen et al
Y. Shen et al. , Amyloid fibril systems reduce, stabilize and deliver bioavailab le nanosized iron. Nature nanotechnology 12, 642-647 (2017)
2017
-
[52]
Boisen, J
S. Boisen, J. Fernández, Prediction of the total tract digestibility of energy in feedstuffs and pig diets by in vitro analyses. Animal Feed Science and Technology 68, 277-286 (1997). Fig. 1 Illustration of the tandem emulsification systems for fabricating plant protein microc...
1997
Reviewed August 11, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.