Understanding lubrication and perception of foods

20 June 2016 - New insight into the rheological and tribological behaviour of particles in liquid and semi-solid foods, and their effects on food perception, is the main outcome of Kun Liu’s PhD project.

Both structural and textural perception of foods undergo dynamic changes during mastication. These changes are influenced by the rheological (large deformation & viscosity) and tribological (lubrication) properties of the foods.

Liu studied the relationship between these properties and the sensory perception of different foods. “Imagine the ball-bearing system which makes so many parts of a modern bicycle run smoothly”, she explains. “I investigated ball-bearing mechanisms of microparticles in liquid model foods, which represent milk or other dairy drinks, as well as solid model foods, which represent cheese or sausages.”

Previous research focussed on only one type of food systems, either solid or liquid. “I was the first to study and compare both types, in order to identify similarities and differences between the two”, the scientist explains. ”The interaction between the food particles and the solid food matrix has a large influence on the rheological, tribological and the sensory properties of foods.”

Morphology, size, and deformability of food particles appear to determine the lubrication behaviour of the foods. “Spherical particles with a few micrometres in size, such as microparticulated whey protein, reduced friction through a ball-bearing-like process; irregularly-shaped particles, such as uncooked rice starch, increased friction as their irregularity also increased their surface contacts”, she illustrates. “Deformable particles could flatten the surface by evening-out asperity (the term used in materials science for unevenness) and coalescence of unstable droplets could plate-out on the surface and form film patches; both mechanisms reduced friction”. Other structural elements, such as emulsifiers and sticky molecules, also affected tribological properties by influencing the surface interaction between the structure elements and the surfaces.

Prediction of sensory perception

The work offers the industry new ways to develop and optimise products. “Based on the findings, I developed a model that allows prediction of sensory perception of particle-filled foods, based on their rheological and tribological properties”, says Liu. “It can be applied to a wide range of products, from dairy to meat.”

The scientist, nominated for the TiFN’s annual Publication Prize, is very enthusiastic about her time as a PhD fellow at TiFN. “I enjoyed the freedom to go to conferences and workshops, and the opportunity to promote my research and discuss my work with researchers globally.”

Round creamy cheese, with a wedge cut out, isolated on white background.