Janus starch particles: Synthesis and characterization

Abstract

Starches are one of the most widely used ingredients in the food industry, owing to their incredible versatility as texturizers and emulsifiers. To fine-tune their properties for a wide array of applications, over 100 kinds of modified starches have been made in the last 70 years by homogeneous methods—via chemical, enzymatic, and physical means—to produce one-faced particles, i.e., particles whose entire surface has been modified to have only one and the same physical or chemical functionality. Very little research, however, exists on the potential applications of the heterogeneous modification of starch to produce Janus or two-faced particles, i.e., particles with two opposite halves that have two different functionalities. In this dissertation, various methods were explored to synthesize starch Janus particles and characterize their self-assembly, texturizing, and emulsifying abilities. In Chapter 1, a 2D mask approach via a spin-coating spray method was developed to produce half-hydrophobic, amaranth starch Janus granules by octenyl succinic anhydride (OSA) esterification. These Janus particles were found to exhibit unique self-assembly behavior into worm-like strings. Low yield, however, prevented further characterization, so a more scalable 3D mask approach via a wax Pickering emulsion method was developed next. To make this method work, however, starch’s emulsifying ability first had to be improved so it could embed itself halfway into a wax droplet. In Chapter 2, it was found that retaining a high protein content when extracting starch from flour played a key role in making sure the starch would embed itself halfway into the wax droplet. In Chapter 3, using these high-protein starches, a scalable 3D mask approach was then developed that could make Janus particles with 49% Janus balance. Janus starch granules with one half side modified with OSA were found to self-assemble into worm-like strings in water. These Janus starch granules outperformed the unmodified and homogeneously modified controls as thickening and gelling agents, as evidenced by their fourfold increase in water-holding capacity, a 30% lower critical caking concentration, a viscosity greater by orders of magnitude, and their formation of gels that were stiffer and stronger also by orders of magnitude. In fact, such was the improved thickening ability of these Janus starch particles that we could achieve similar viscosities as the controls by using less than half the amount of Janus starch. These Janus particles thus show promise as high-performance, plant-based texturizers for potential calorie reduction, pointing to an emerging field of food-based Janus particles that, if pursued, may bring to the table exciting, new applications in the future of our food.