Role of proteins in the microstructure, rheology, tribology and sensory perception of plant-based custards

Custard is a dairy dessert typically composed of milk, egg yolk, starch and sugars. In recent years, the food market has shown an increased demand for plant-based dairy alternatives. This study evaluated the role of plant-protein isolates (namely pea, potato and soy) in the physicochemical, rheological and microstructural characteristics of plant-based (no-dairy, no-egg) custards and in their sensory perception. The protein isolates were selected based on differences in gelling behaviour and were tested at three different concentrations (2.5, 4 and 10%) under the same process conditions. The results were compared to both a conventional dairy-based custard with egg yolk and a plant-based formulation without proteins. In general, custards were characterized by a microstructure of swollen starch granules and a protein network. Increasing protein concentration enhanced the continuity of the protein network, which increased viscosity and exerted a space limiting effect on the swollen starch granules. The viscosity of the custards positively correlated to mouth-coating, compactness and stickiness perception. Melting rate perception was negatively related to thickness and compactness. The particle size of the protein aggregates was positively related to graininess perception and negatively with creaminess. Potato proteins formed a dominant network already at low concentrations and the substantial enhancement in elastic behaviour and viscosity had negative effects on texture perception of the plant-based custards compared to the animal-based reference. On the contrary, soy and pea protein formed at low concentrations less extensive networks compared to potato, resulting in rheological properties most closely resembling those of the reference custard. However, pea protein showed a tendency to form a less homogeneous protein network with large aggregates, that negatively affected creaminess. Overall, under the conditions of this study, matching particle size of the protein aggregates, viscosity, G’ and critical strain led to plant based samples with mouthfeel attributes similar to those of the animal-based reference. • Three plant-proteins were studied in a egg- and milk-free custard application • The protein phase was key in determining the microstructure and texture of custards • The protein network enhanced thickness, compactness and mouth-coating by viscosity increase • Protein aggregates reduced creaminess by enhancing graininess perception • Soy protein isolate led to a plant-based custard with sensory properties similar to the reference