Solubility and aggregation state govern foam performance of lab-extracted and commercial soy proteins

Accurate prediction of the macroscopic foaming properties of soy protein ingredients is limited due to variability in composition, processing history and molecule-related ingredient properties. Molecule-related properties are intrinsic properties of individual protein molecules or aggregates that govern how proteins behave, interact, and arrange themselves. This study investigated the relationship between molecule-related properties and foaming behavior of soy proteins. Key properties, including solubility, particle size, surface charge, 11S/7S ratio, denaturation enthalpy, and surface tension, were characterized and evaluated in relation to foam properties, namely overrun and half-life time. Lab-extracted soy proteins were found to be partially native, as shown by differential scanning calorimetry, whereas commercial proteins were fully denatured. For lab-extracted proteins, both positive foaming effects and negative aggregate-related effects on foam behavior were observed. The foaming effect appears to be diffusion-driven, as higher solubility increases the number of proteins available for adsorption, while smaller particle size and lower surface tension may enhance foam properties. Conversely, protein aggregates may impair foam properties through reduced protein availability in the bulk and development of interfacial and/or film instabilities. These effects are associated with changes in solubility, hydrophobic and electrostatic interactions, and increased particle size. In contrast, for commercial proteins, foam stability appeared to be primarily governed by solubility (R 2 =0.81), with other parameters having little effect (|R 2 | between 0.09-0.38), likely dominated by aggregates. Therefore, in commercial proteins, only negative aggregate-related effects were observed. These findings showed that molecular-macroscopic relationships are present for lab-extracted ingredients, but when extensive protein aggregation occurs, these relationships are invalid.