Supervisors: Dr. Arnout Imhof and Dr. Krassimir Velikov
Promotor: Prof. dr. Alfons van Blaaderen
Funding: STW (St. Technische Wetenschappen)
Employed: 1 June 2015 – 30 May 2019

Synthesis and characterization of bio-based colloidal colorants

The aim of this project is to design optically functionalized nanoparticles from water insoluble proteins as a technology platform for the delivery of colorants. The protein chosen for this work is zein, a prolamine from corn. Zein is edible, renewable, and biodegradable. In addition, zein is soluble in food safe solvents and it is capable of film formation with good barrier properties. These are all properties that are advantageous for possible future applications in food or cosmetics.

This project is divided into two main parts. The first part of this project is to design a colloidal dispersion that has a white appearance (figure 1a and b). The motivation for this is to develop a bio-based and renewable alternative for the inorganic titanium dioxide (E171) as a white colorant in wet food products [1, 2]. To synthesize these white colorants, zein is purified and converted into stable colloidal particles via anti-solvent precipitation. The second is to encapsulate other colorants by co-precipitation of the colorants with zein (figure 1c and d). Both types of particles, white and colored, are then characterized on the single particle level and in concentrated suspensions. On the single particle level characterization is done by UV-Vis spectroscopy and dynamic light scattering. In concentrated suspensions, characterization is done by total reflection and total transmission measurements. And finally the experimentally found scattering properties of the particles are compared to theory.

Figure 1: White zein colloids after synthesis a) and corresponding SEM image b), and blue zein colloids after synthesis c) and corresponding SEM image d).

[1] A. Weir et al., Environmental Science and Technology 46, 2242-2250 (2012)

[2] M. Lomer et al., Analyst 125, 2339-2343 (2000)