Crystallization in Emulsions: A Thermo-Optical Method to Determine Single Crystallization Events in Droplet Clusters

Tuning interfacial properties of phospholipid stabilised oil-water interfaces by changing the phospholipid headgroup or fatty acyl chain

HYPOTHESIS

In-plane interactions among adsorbed phospholipids (PL) at an oil-water interfacial film may vary based on the size of the headgroup or the size and saturation of the fatty acyl chain (FA). In general, stronger interactions are expected when the PL can approach each other closer, when 1) the headgroup is smaller and 2) the FA chain is straight, allowing a good alignment. Also, varying pH might alter PL-PL interactions, as electrostatic forces between the adsorbed PL will decrease with decreasing pH (lower number of charged groups).

EXPERIMENTS

The interfacial layers formed by saturated/unsaturated phosphatidylethanolamine and phosphatidylcholine were characterised after a heat-cool cycle as a function of their molecular structure and pH, using dilatational and interfacial shear rheology.

FINDINGS

For the same FA chain, a smaller headgroup resulted in a stiffer interface. In the case of the saturated PLs, network formation due to chain crystallisation of the PL's FA chains occurs during cooling, increasing elasticity. The bend in the molecule of unsaturated PLs hinders the PL from packing tightly on the interface, leading to weaker PL-PL interactions and, accordingly, less stiff interfaces. In general, the stiffness of the interface increases with decreasing pH as the degree of ionisation is lowered, electrostatic repulsion forces are reduced and with it, overall in-plane attraction between PLs are enhanced.

A review of electrochemical sensing in droplet systems: Droplet and digital microfluidics

BACKGROUND

Microfluidic technologies based on droplets provide discrete volumes within which chemical and/or biological processes can take place. Two major platforms in this space include droplet microfluidics (emulsions within channels) and digital microfluidics (discrete droplet manipulation by electric fields). The integration of electrochemical sensing with both microfluidic platforms offers advantages in miniaturization and portability, as sensors can be integrated directly within the microfluidic devices and instrumentation is relatively compact.

RESULTS

This review provides background on droplet and digital microfluidic technologies and electrochemical sensing before moving to methods and applications. A discussion of the various strategies to integrate sensing electrodes with both droplet and digital microfluidics and the merits of each method are included. A review of the many different applications of these integrated systems is provided.

SIGNIFICANCE AND NOVELTY

To date, there are no reviews that solely focus on the integration of electrochemical sensing with droplet and digital microfluidics. There are many advantages to combining electrochemical sensing with these platforms, especially for applications where portability or small form factors are paramount. While early reports on integrating electrochemical sensing with droplet and digital microfluidics are more than a decade old, the field is still relatively nascent, offering opportunity for many applications.

Changing the Oral Tribology of Emulsions Through Crystallization of the Dispersed Triglyceride Phase

Suspoemulsions are used for food, cosmetic and pharmaceutical products, including food such as dairy products and non-dairy alternatives. Product properties, such as flow behavior or sensory perception of non-dairy products differ from those of dairy products and are therefore perceived by consumers as products of inferior quality. One reason for this may be the crystallization behavior of the added triglycerides leading to differences in solid fat content in comparison to cow milk. This is discussed with the solidity of the dispersed phase as a parameter of suspoemulsions. The solidity was varied by using low and high melting triglycerides and measuring at different temperatures. The dispersed phase fraction is φ = 30%. The droplet size distribution showed a x50,3 of 1.2 and 3.66 μm, mimicking the droplet sizes of milk and dairy cream. Rheological frequency sweeps were carried out within a temperature range from 5°C to 50°C. The differences in solidity of the dispersed phase caused no changes in viscosity at each temperature. In contrast, oral tribology distinguished different solidities of the dispersed phase with changes in the friction coefficient. The friction coefficient was determined for increasing rotational speeds (0.01-100 mm/s), to compare the so called Stribeck curves with each other. In general, with increasing solidity of the dispersed phase, the friction coefficient increases. Comparing the Stribeck curves of pure butter fat suspoemulsion with those of plant-based fat suspoemulsions, different plant-based fats can be mixed, to mimic the friction profile of milk products in plant-based alternatives.

(Non)linear Interfacial Rheology of Tween, Brij and Span Stabilized Oil-Water Interfaces: Impact of the Molecular Structure of the Surfactant on the Interfacial Layer Stability

During emulsification and further processing (e.g., pasteurizing), the oil-water interface is mechanically and thermally stressed, which can lead to oil droplet aggregation and coalescence, depending on the interfacial properties. Currently, there is a lack of insights into the impact of the molecular structure (headgroup and FA chain) of low molecular weight emulsifiers (LME) on the resulting interfacial properties. Additionally, the crystallization/melting of the oil/the emulsifier is often neglected within interfacial rheological experiments. Within this study, the stability of interfaces formed by Tween, Span or Brij was determined as a function of their molecular structure, taking crystallization effects of the LME into account. The headgroup was kept constant while varying the FA, or vice versa. The interfacial film properties (viscoelasticity) were investigated at different temperatures using dilatational and interfacial shear rheology. Both the headgroup and the FA chain impacted the interfacial properties. For the same FA composition, a rather small hydrophobic headgroup resulted in a higher packed interface. The interfacial elasticity increased with increased FA chain length (C12 to C18). This seemed to be particularly the case when the emulsifier crystallized on the interface among cooling. In the case of a densely packed interface, network formation due to chain crystallization of the LME's FA chains occurs during the cooling step. The resulting interface shows predominantly elastic behavior.

Emulsions of miscible solvents: the origin of anti-solvent crystallization

Emulsions of miscible solvents: the origin of anti-solvent crystallization. We demonstrate that emulsions in a miscible solvents system could provide the opportunity to explain an accurate mechanism of anti-solvent crystallization before nucleation.

Food Structure Development in Emulsion Systems

A number of food products exist, in part or entirely, as emulsions, while others are present in an emulsified state at some point during their production/formation. Mayonnaise, butter, margarine, salad dressing, whipped cream, and ice cream represent some of the typical examples of emulsion-based foods. Controlled by both formulation and processing aspects, the emulsion architecture that is formed ultimately determines many of the attributes of the final food product. This chapter initially provides an overview of the basic constituents of emulsions and their influence on the microstructure and stability of conventional as well as more complex systems. The available spectrum of processing routes and characterization techniques currently utilized (or emerging) within the area of emulsions is then discussed. The chapter concludes with a concise outline of the relationship between food emulsion microstructure design and its performance (textural, rheological, sensorial, etc.).