Philippe Rousset

A Tribological Model for Chocolate in the Mouth: General Implications for Slurry-Lubricated Hard/Soft Sliding Counterfaces

We have investigated the rheological and lubrication properties of molten chocolate samples. To this end, a series of chocolate samples having various textural/compositional features have been prepared. The rheological properties of the chocolate samples are discussed in terms of the Casson model. The lubrication properties of the molten chocolate samples have been characterized by means of pin-on-disk tribometry. For the tribo-pairs, zirconia (ZrO2) and poly(tetrafluoroethylene) (PTFE) have been used in all permutations for both slider (pin) and track (disk), providing the four tribo-pair combinations; ZrO2/ZrO2, PTFE/ZrO2, ZrO2/PTFE, and PTFE/PTFE. The results showed that both the rheological and lubrication properties of the chocolate samples are strongly influenced by the textural and compositional characteristics. The lubrication properties are further influenced by the choice of the tribo-pair. The different lubrication properties of the chocolate samples at different tribo-pairs are discussed in terms of particle behavior in the surrounding region of the inlet of the sliding tribo-pairs.

Influence of homogenization on physical properties of model coffee creamers stabilized by quillaja saponin

There is a growing demand for use of natural ingredients in food manufacturing. This study utilized a natural emulsifier, quillaja saponin (1%) to fabricate non-dairy model creamer emulsions (containing 10% medium chain triglycerides oil). Varying homogenization conditions, ranging from a high-shear mixer to passing through a microfluidizer at 20,000psi, were applied to fabricate emulsions. The effect of particle size on the appearance, tristimulus color coordinates, and electrical characteristics of the model creamers and white coffee drinks were investigated. The average droplet size varied from 0.2 to 16μm. All model creamers had whitish milk-like appearance and the white coffee solutions had light brown color. All systems were physically stable except for the systems with largest oil droplets (1.8 and 16μm), which had creaming. The lightness, L* (whiteness) of the model creamer and the white coffee increased with decreasing oil droplet size, as smaller droplets scatter more light. Decreasing the oil droplet size led to lower zeta potential (from -73 to -54mV) due to lesser negative charge group accumulated on the interfacial layer of the droplets. The oil droplets were also found to be stable to aggregation in hot acidic coffee solutions prepared using model hard water. Overall, this study found that oil droplets stabilized with natural plant-based surfactant have potential for application in liquid coffee creamers and their stability and whitening power were dependent on the droplet size.

Impact of oil droplet concentration on the optical, rheological, and stability characteristics of O/W emulsions stabilized with plant-based surfactant: Potential application as non-dairy creamers

The development of plant-based foods and beverages is becoming increasingly popular because of growing consumer concerns about perceived ethical, health, and environmental issues. The current study examined the influence of oil droplet concentration on the physicochemical properties of oil-in-water (O/W) emulsions stabilized with a plant-based surfactant. Emulsions were utilized as model creamers, which consisted of medium chain triglycerides (MCT) as the oil phase and quillaja saponin as a plant-based surfactant. The optical, rheological and stability properties of these model creamers were measured at varied oil content from 0 to 15%, at a constant surfactant-to-oil ratio (1:15). The model creamers had an appearance similar to that of commercial non-dairy creamers, and their whiteness increased with increasing droplet concentration due to enhanced light scattering: L* from 77 to 91 for creamer and L* from 5 to 55 for white coffee. The quillaja saponin-coated lipid droplets were stable to aggregation and gravitational separation when added to hot acidic coffee solutions (85°C, pH4.9), which was attributed to strong steric and electrostatic repulsions. The apparent viscosity of the model creamers increased with increasing droplet concentration due to increased frictional losses associated with the presence of the droplets. This study provides valuable information into the impact of oil content on the physicochemical properties of liquid creamers using plant based surfactants, which is important for the formulation of healthier products.