The role of surface properties on the physical attributes and stability of cocoa powder systems

Cocoa is widely used by confectionary industries as a powder raw material for chocolate production. The chemical properties such as high- or low-fat content determine the functionality of the cocoa powder and constitute as a major factor in controlling the behavior of the final product. Additionally, the physicochemical properties such as the cohesive characteristics of cocoa powders create undesirable issues in industrial manufacturing settings. Thus, the evaluation of physical and chemical attributes is relevant to differentiate the powder surface structure and define the material behavior in presence of other materials or distinct environments.

This work evaluated three kinds of cocoa powders—varying mainly on the lipid content—to assess the powder performance in terms of the role of surface properties on the physical attributes (flowability and wettability) and stability under distinct frameworks. Various analytical tools were used, and several methodologies were developed and implemented to determine the surface area, changes in lipid melting phases at the surface level and particle interactions. The characterization methods included particle true density, flow properties under aerated conditions, bulk permeability, thermal properties, surface energetics, water sorption, and chemical surface compositional analyses.

The findings of this work revealed that the cocoa surface composition, amount of lipids, did not explain the low-flow performance or the water uptake. On the other hand, physicochemical properties such as lipid polymorphism was introduced as an avenue to further understand the results. From the surface energetics standpoint, a water diffusion mechanism is proposed as a result of the observed effect of water on the performance and stability of the cocoa powder systems. Owing to the hydrophobic nature of cocoa particles, this material can be used as a unique reference to understand cohesive particle models with implications on the performance (flowability and wettability) of lipid-based surface materials. The results indicated that powder behavior on the performance is a confounding effect of all variables.

The major contribution of this thesis work demonstrates the importance of surface chemistry characterization on the physical attributes of cocoa powder systems and the potential to control surface composition to improve the performance and stability of food complex systems.