Emulsions stabilized by pea protein-rich ingredients as an alternative to dairy proteins for food sustainability: Unveiling the key role of pea endogenous lipids in the surface-induced crystallization of milk fat.

In the current context of food transition, the growing demand of consumers for sustainable plant-based protein sources has stimulated interest of food scientists in plant protein ingredients as alternatives to dairy protein ingredients. In this study, we hypothesized that the crystallization properties of dairy emulsions could be affected by the chemical complexity of commercially available pea protein-rich ingredients that contain proteins but also endogenous lipids. Dairy emulsions (30 %wt milk fat) stabilized either by a pea protein isolate or dairy proteins were prepared, their microstructure and interfacial composition were characterized. The crystallization and melting properties of milk fat in anhydrous state and in the emulsions were examined by the combination of differential scanning calorimetry (DSC) and synchrotron-radiation X-ray diffraction as a function of temperature (SR-XRDT). The results revealed differences in the milk fat crystallization properties in emulsion as a function of the ingredient used and highlighted a specific role played by pea endogenous lipids. The pea protein-rich ingredient contained 12.1 %wt endogenous lipids including 56.2 %wt polar lipids, 40.7 %wt triacylglycerols (TAGs) and 3.1 %wt plant sterols. The partitioning of pea endogenous lipids occurred upon emulsion formation as a function of their polarity: liquid unsaturated fatty acid rich pea TAGs mixed with milk TAGs in the core of the lipid droplets while pea polar lipids migrated at the TAGs/water interface together with pea proteins. Pea polar lipids were composed of saturated high melting temperature (T_m) and unsaturated low T_m molecular species. High T_m pea polar lipids exhibited a phase transition on cooling (from L_α/expansed to L_β/condensed) and acted as interfacial templates for surface heterogeneous nucleation and crystal growth of high crystallization temperature milk TAGs. The key interfacial and functional roles played by pea endogenous lipids present in the protein isolate were demonstrated. This study highlights the importance to examine the chemical composition and the properties of plant-based ingredients that are increasingly used for sustainable food formulations.