Phospholipids and hydrolysates from a sunflower protein isolate adsorbed films at the air–water interface

The surface activity of mixed films of phospholipids (dipalmitoyl-phosphatidyl-choline, DPPC, dioleoyl-phosphatidyl-choline, DOPC, and dipalmitoyl-phosphatidyl-ethanolamine, DPPE) and sunflower protein isolate (SPI) and its hydrolysates at different degrees of hydrolysis (DH=5.62%, 23.5%, and 46.3%) was studied. The surface pressure data were determined by the Wilhelmy plate method, over a range of protein concentrations (5–1×10−6 wt%), at pH 7, and at 20 °C. Surface pressure data at low protein concentration indicate low surface activity that rises to a plateau as the monolayer is saturated at higher protein concentrations. The existence of protein–phospholipid interactions depends on the interfacial composition and on the protein/phospholipid ratio. The surface activity of mixed protein–phospholipid films is determined by the protein as the protein saturates the monolayer at higher protein concentrations in the bulk phase. However, the phospholipid increases the surface activity of protein films at low protein concentrations in solution. These results are of practical importance because peptides formed during hydrolysis may be too small to stabilize fluid interfaces, which is essential for the formation and stability of food dispersions (emulsions and foams).