White zein colloidal particles: synthesis and characterization of their optical properties on the single particle level and in concentrated suspensions

Abstract

Growing interest in using natural, biodegradable ingredients for food products leads to an increase in research for alternative sources of functional ingredients. One alternative is zein, a water-insoluble protein from corn. Here, a method to investigate the optical properties of white zein colloidal particles is presented in both diluted and concentrated suspensions. The particles are synthesized, after purification of zein, by anti-solvent precipitation. Mean particle diameters ranged from 35 to 135 nm based on dynamic light scattering. The value of these particles as white colorant is examined by measuring their optical properties. Dilute suspensions are prepared to measure the extinction cross section of individual particles and this was combined with Mie theory to determine a refractive index (RI) of 1.49 ± 0.01 for zein particles dispersed in water. This value is used to further model the optical properties of concentrated suspensions. To obtain full opacity of the suspension, comparable to 0.1-0.2 wt% suspensions of TiO2, concentrations of 2 to 3.3 wt% of zein particles are sufficient. The optimal size for maximal scattering efficiency is explored by modeling dilute and concentrated samples with RI's matching those of zein and TiO2 particles in water. The transport mean free path of light was determined experimentally and theoretically and the agreement between the transport mean free path calculated from the model and the measured value is better than 30%. Such particles have the potential to be an all-natural edible alternative for TiO2 as white colorant in wet food products.

Using a Microfluidics System to Reproducibly Synthesize Protein Nanoparticles: Factors Contributing to Size, Homogeneity, and Stability

“…The results indicate that one washing step was sufficient to remove most impurities from the Zein. Similar results were shown by De Boer et al [28]. To verify that the colored impurities were removed, the absorption spectra of the diluted unpurified and purified Zein solutions were compared using UV-Vis ( Figure A4d).…”

“…The batch-to-batch consistency between trials: (a) the diameter of Zein nanoparticles (NPs) using a syringe pump synthesis under standard conditions, n = 36; (b) the polydispersity (PD) of Zein NPs using a syringe pump synthesis under standard conditions, n = 36; (c) the diameter of Zein NPs using a syringe pump synthesis under standard conditions with stabilizers [0.5% Tween 80 (TW80) 1.0% Pluronic F-68 (PF-68)], n = 9; (d) the PD of Zein NPs using a syringe pump synthesis under standard conditions with stabilizers (0.5% TW80 1.0% P-F68), n = 9; (e) the diameter of Zein NPs using a syringe pump synthesis under standard conditions other than relative flow rate (RFR) [RFR 1:5], n = 27; (f) the PD of Zein NPs using a syringe pump synthesis under standard conditions other than RFR [RFR 1:5], n = 27; (g) the diameter of Zein NPs using a syringe pump synthesis under standard conditions other than RFR [RFR 1:5] with stabilizers (0.5% TW80 1.0% PF-68), n = 9; (h) the PD of Zein NPs using a syringe pump synthesis under standard conditions other than RFR [RFR 1:5] with stabilizers (0.5% TW80 1.0% P-F68), n = 9; (i) the diameter of Zein NPs using a batch synthesis method, n = 2; (j) the PD of Zein NPs using a batch synthesis method, n = 2; (k) the diameter of Zein NPs using a syringe pump synthesis with a T-Junction under standard conditions, n = 9; and (l) the PD of Zein NPs using a syringe pump synthesis with a T-Junction under standard conditions, n = 9. [28,48]. The presence of these impurities has been known to increase the polydispersity of Zein NPs and decrease their drug encapsulation efficiency; therefore, it can be understood why there have been increasingly more efforts put into purifying Zein [28,48,50].…”

“…These findings suggest that a Y-channel microfluidics chip could be a suitable candidate in producing small, monodisperse Zein NPs for pharmaceutical applications, such as drug delivery. Zein contains removable, colored impurities, such as xanthophylls (including lutein, zeaxanthin, and β-cryptoxanthin) and b-carotene [28,48]. The presence of these impurities has been known to increase the polydispersity of Zein NPs and decrease their drug encapsulation efficiency; therefore, it can be understood why there have been increasingly more efforts put into purifying Zein [28,48,50].…”

“…Zein purification was adapted from De Boer et al [28]. Zein (0.10 g) was suspended in 15 mL of anhydrous ethanol.…”

Functional and Engineered Colloids from Edible Materials for Emerging Applications in Designing the Food of the Future

“…In a very recent study, zein colloidal particles have also been proposed as alterative to titanium dioxide (TiO 2 ) as white colorant in food products . Although, TiO 2 is currently the best known and most widely used white food colorant, recent concerns regarding the toxicity of nanosized TiO 2 has prompted the need for finding safer alternatives.…”