Balancing oil and protein content: antifoam regimes of foamed protein-based emulsions

The presence of liquid oil droplets in protein-based systems can reduce foaming functionality through antifoam activity. However, no systematic study on regimes of antifoam activity at different protein and oil contents is currently available for foamed food emulsions. Soy protein solutions, containing mostly unaggregated proteins, were foamed in the presence of different amounts of protein-stabilized sunflower oil droplets, added in the form of different amounts of a pre-prepared emulsion with controlled droplet size distribution. This experimental approach allowed systematic investigation of the effects of soy protein and oil content on antifoam activity. Oil contents as low as 0.006 wt% caused notable foamability reductions. Highest antifoam activities were observed at 0.1 wt% of oil with drastic foamability reductions (>60 %) at low to moderate protein contents (0.1–0.7 %). Surprisingly, increasing oil contents above 1 wt% resulted in significantly lower antifoam activities with, finally, complete or near complete foamability recovery at oil contents of 10 or 25 wt%, depending on the protein content. Increasing protein content in the presence of 0.1 wt% oil always resulted in antifoaming activity reduction, until foamability was fully restored at the highest protein contents (>1 wt%). Remarkably, similar trends of these regimes of antifoam activity were observed for multiple other protein types (skim milk, egg white, and potato) and different oil types (rapeseed and corn). Using bubble monolayer tests, it was observed that bubble bursting at the foam surface was the main destabilization mechanism. Thus, this paper highlights and quantifies the existence of generic regimes of oil droplet-based antifoam activity in foamed protein-based emulsions with low to moderate protein and oil contents.