Minerals govern the physico-chemical properties and structural organisation of milk polar lipids

Minerals found in milk have a complex composition which evolves according to pH and technological processes. Among milk components, polar lipids (phospholipids and sphingomyelin) are amphiphilic molecules with a polar head group highly sensitive to ions. Milk polar lipids are mainly located in the membrane surrounding fat globules. They can also be concentrated from by-products of the dairy industry (e.g. buttermilk) and used for their interesting nutritional and functional properties as well as for encapsulation after formation of liposomes. Although the minerals found in milk and dairy products can affect the functional properties of polar lipids and their structural organisation, scientific data are scarce. The objective of the work was to investigate the properties of milk polar lipids as a function of the pH, the ionic strength and the type of minerals: monovalent or divalent ions. The combination of chemical and biophysical methods (zeta potential, turbidimetry, microscopy techniques) was used to characterise polar lipids properties and organisation. Changes in milk polar lipids properties and organisation will be presented as a function of their mineral environment. Decrease in pH and increase in ionic strength lead to a reduction i) of zeta-potential values, ii) of the electrostatic repulsions between polar lipids particles until their aggregation and phase separation from water. Among milk minerals, calcium highly affects polar lipids properties. This work contributes in a better understanding of the physical stability of milk fat globules and will improve the utilization of milk polar lipids for different food applications (cheeses, infant formulas…).