Research of the mechanism of the impact of dispersion additives on the rheological properties of disperse systems based on wheat flour

In the paper the requirements to the physicochemical properties of the potential substitutes of the used food additives are considered. Cocoa is one of the products that is constantly looking for its potential substitutes. Studies have shown that when added to aquatic systems, cocoa is divided into two components: substances that pass into the volume of the system and are evenly distributed in it due to the passage of extraction processes, and resistant to the external influence of particles that swell and become nodes of the spatial structural network. Potential substitutes for cocoa in confectionery should not only preserve the relevant organoleptic properties of the final product, but also reproduce the behavior of cocoa in semi-finished products. We have shown that the separation of cocoa into soluble and insoluble component occurs in the ratio of 3: 1. The obtained results allow us to predict that in such systems the soluble component exerts a greater influence on their rheological characteristics. It has been found that the introduction of cocoa flour and its ingredients leads to a gradual increase in the viscosity of the dough. This is due to the processes of structure formation in the dispersed systems due to the leaching of substances from cocoa. It should be noted that cocoa powder works most effectively, the water-soluble component is less effective and finally the insoluble component has little effect on the viscosity of the dough samples. This indicates the decisive role of the intensity of interparticle interaction in the processes of structure formation in such systems. Substances that are contained in a water-soluble component capable of forming bridging bonds contribute to the formation of structure in the system. Purely mechanical impurities (insoluble component) have virtually no effect on the rheological characteristics of the system. It was found that the total effect of cocoa components on rheological characteristics is less than the effect of cocoa powder as a complex additive. This indicates that particles of the dispersed phase of a water-insoluble cocoa component are more likely to form a structural framework with molecules of a water-soluble component of cocoa. Therefore, the chemical affinity of soluble and insoluble components plays an important role in the structuring of dispersed systems based on wheat flour.

Segregation in dissolving binary-component sessile droplets

The dissolution of a single droplet, containing a mixture of oils, in water is experimentally studied. The oils in the droplet varied in terms of their solubility in water and their hydrophobicity. We demonstrate that the polarity of the droplet constituents strongly influences the dissolution dynamics. A binary-component droplet, containing two polar components (one soluble the other insoluble) exhibits a retarded dissolution as compared to a droplet containing only the soluble component. We argue that in this case the mixture in the droplet can be assumed homogeneous, leading to a smaller effective contact area of the soluble liquid in the droplet with the bulk water, and thus delayed dissolution. On the other hand, it is shown that this is not the case when a polar, soluble component is mixed with an insoluble non-polar component, in which case segregation between the different liquids inside the droplet occurs, leading to Marangoni flows and superspreading of the droplet. The segregation is confirmed by volumetric measurements and by the use of a solvatochromic dye in combination with confocal microscopy, which clearly showed that during dissolution local concentration differences inside the droplet developed.