Relation between solubility and surface hydrophobicity as an indicator of modifications during preparation processes of commercial and laboratory-prepared soy protein isolates

Because water solubility is the main hydration property of proteins, solubi lity values of commercial and laboratory soy protein isolates, prepared und er different conditions, were comparatively analyzed. In contrast, the surf ace hydrophobicity manifested by proteins is a physicochemical property tha t determines, to a great extent, the tendency of protein molecules to aggre gate and so to lose solubility. On these grounds, the solubility of isolate s was analyzed as a function of the surface hydrophobicity of their protein s, and, as a result, three well-defined groups of laboratory isolates were identified: (A) native, (B) partially or totally denatured with high solubi lity and surface hydrophobicity, and (C) totally denatured with low solubil ity and surface hydrophobicity. Commercial isolates could not be included i n any of these groups; they were grouped as (A') partially native and (C') totally denatured. Solubility values in these two groups were similar to th ose of group C-2 but the surface hydrophobicity levels were much lower. The different processes leading to the groups mentioned above are discussed, a long with the way the soy proteins are influenced by the specific preparati on conditions, namely, protein concentration, chemical or thermal treatment s, presence of salts, drying, and phospholipid addition, among others.