Zein colloids as an edible white colorant


Well-designed colloidal particles are essential in current industrial setups owing to the vast applications they have in terms of controlling product appearance. Such an attribute is achievable through manipulation of shape, composition and particle size; the attributes that control how the particle interacts with light.

Of course visual product appearance is essential in food industry. Research has shown that color and other appearance attributes create the first impression and primary perception of the consumer toward the food product. Presently, titanium dioxide is the most used white food colorant. However, concerns have been raised regarding the toxicity of nanosized titanium dioxide. Therefore, to avert a potential crisis, development of a natural, bio-based class of materials to use in the synthesis of colloidal particles would be highly desirable. In line with this, prolamins have shown promising attributes and bring along many advantages for the aforementioned purpose. In particular, zein- a group of highly hydrophobic proteins derived from corn- has shown promising attributes. Unfortunately, no research has been undertaken to assess on the usability of zein as a white colorant in food applications to serve as an all-natural and edible replacement for the inorganic titanium dioxide.

Recently, a team of researchers at Utrecht University: Frankje de Boer (PhD candidate), Rutger Kok (PhD candidate), Professor Arnout Imhof and Professor Krassimir P. Velikov investigated the possibility of using zein as an alternative white colorant for wet food products such as mayonnaise, dressings and beverages. Particularly, they assessed the whiteness of zein particles in a suspension with no excessive components. Their work is currently published in the research journal, Soft Matter.

In brief, the researchers commenced the experimental work by first, purifying zein so as to remove colored impurities. Next, they synthesized white zein nanoparticles using anti-solvent precipitation. The particle shape, charge and size of the zein nanoparticles were then measured. They then quantified the synthesized nanoparticles as white colorant by measuring their scattering properties. Lastly, the optical properties of concentrated suspensions were determined.

The authors observed that the refractive index of the zein particles was 1.49 ± 0.01. In addition, they noted that the transport-mean free path of light determined experimentally and theoretically, was in agreement with the transport-mean free path calculated from the model. In fact, the measured value was seen to be better than 30%. All in all, the results obtained showed that it was possible to model the scattering behavior of suspensions of zein particles.

In summary, the study by Utrecht University scientists presented the successful synthesis of white zein colloidal particles using the anti-solvent precipitation technique. Generally, it was seen necessary to increase the concentration of zein particles in the test solution so as to match opacity to that of titanium dioxide. Altogether, these particles have the potential to be an all-natural edible alternative for titanium dioxide as white colorant in wet food products.

Zein colloids as an edible white colorant - Advances in Engineering

About the author

Currently, Frankje de Boer is in her last year as a PhD student in the Soft Condensed Matter and Biophysics group, within the Debye Institute of Nanomaterials Science at Utrecht University in the Netherlands. Her research focuses on the synthesis and optical characterization of colloidal colorants from water insoluble proteins, directed towards food applications.

Before starting her PhD, Frankje studied Chemistry at Avans University of Applied Science in Breda where she obtained a bachelor’s degree in 2012, specializing in polymer and analytical chemistry. Following in 2015, she obtained her master’s degree in Chemical Engineering at Eindhoven University of Technology, with a specialization in polymers and composites. At Eindhoven, she performed research in the field of functional coatings with an emphasis on the syntheses and characterization of hydrophilic coatings for biomedical and industrial applications.

About the author

Rutger Kok studied Chemistry at Utrecht University (The Netherlands), where he obtained his M.Sc. in 2018. His master’s thesis at the Debye Institute was about the synthesis and the scattering and absorption properties of nanoparticles made of zein. Recently, he started his Ph.D. research at AMOLF (Amsterdam, The Netherlands) in Developmental Biology under the supervision of Prof. Sander Tans and Dr. Jeroen van Zon. He takes an interest in self-assembly: how seemingly simple starting conditions can lead to the formation of complex systems.

His Ph.D. project is about organoids, which are mini-organs grown in vitro. Starting from stems cells on a plate, structures are formed that closely mimic normal organ tissue. By tracking all cells in part of the organoid using time-lapse microscopy, it is now possible to study organ development and renewal on a cellular level.

About the author

Arnout Imhof is an associate professor in the Department of Physics and the Debye Institute for Nanomaterials Science at Utrecht University, The Netherlands. He earned his PhD in physical chemistry from Utrecht University in 1996 and did postdoctoral research at the University of California, Santa Barbara and at the University of Amsterdam.

His research interests include the synthesis of new types of monodisperse colloidal particles with well-defined composition, shape, and interactions. Using microscopy and scattering methods he studies their self-assembly into soft materials responsive to shear flow or electric fields.

About the author

Krassimir P. Velikov is a Senior Science Leader at Unilever R&D Vlaardingen and adjunct Professor, Chair in Soft Condensed Matter Physics, at the Institute of Physics, University of Amsterdam, The Netherlands.

His research interests cover various topics of soft-condensed matter, colloid and interface science of dispersions (e.g. suspensions, emulsions, foams) and their uses to control product functionality (e.g. stability, appearance, texture, bioaccessibility), physical-chemistry of digestion, and formulation and delivery of functional ingredients.

He also holds part time positions in the Soft Condensed Matter group at the Debye Institute for NanoMaterials Science, University of Utrecht and in the Department of Chemical and Biomolecular Engineering, North Carolina State University.


F. Y. de Boer, R. N. U. Kok, A. Imhof K. P. Velikov. White zein colloidal particles synthesis and characterization of their optical properties on the single particle level and in concentrated suspensions. Soft Matter, 2018, volume 14, page 2870.

Go To Soft Matter

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