Selective proteolysis of β-conglycinin as a tool to increase air-water interface and foam stabilising properties of soy proteins

Proteolysis of food proteins changes their conformation and often generates bioactive peptides, leading to improved nutritional value and techno-functional properties. Protein isolates that originated from plants are generally a mixture of several proteins. Enzymatic hydrolysis of such mixtures has a drawback, as it is often unclear which proteins in the mixture are hydrolysed, leading to poorly reproducible outcomes. In the present study, we applied a controlled methodology, called selective proteolysis, and investigated its effects on the air-water interface and foam stabilising properties of soy protein isolate (SPI). We selectively hydrolysed 7S β-conglycinin of SPI, while 11S glycinin remained relatively intact. Hydrolysates were obtained at two different degrees of hydrolysis (DH). Selective hydrolysis resulted in increased surface activity, and a higher foamability, which nearly doubled. The size of the peptides seemed to significantly affect the mechanical properties of the layer at the air-water interface, which was studied by removing peptides smaller than 14 kDa via dialysis. Peptides smaller than 14 kDa were found to hinder the interfacial network formation, while peptides larger than 14 kDa increased the interfacial stiffness. This was also reflected in the foam stability, as the hydrolysate with a low DH resulted in significantly higher foam stability than the hydrolysates with higher DH. We demonstrated that the selective proteolysis of β-conglycinin can increase the soy protein interface and foam stabilising properties, which could lead to new healthy and more sustainable food products.