Resistance of Soybean Pectin-Protein Conjugate Pre-Adsorbed to the Air-Water Interface to Displacement by the Competitive Adsorption of Surfactant

The naturally occurring soybean pectin-protein conjugate pre-adsorbed to the air-water interface was shown to be displaced competitively from the interface when a small molecule surfactant was added to the aqueous phase. The soybean pectin containing covalently linked pectin-protein conjugate was prepared by heating defatted soy flour at 121 degrees C and pH 4.5 for 2 h. The pectin moiety of the pectin-protein conjugate was cleaved using an alkali treatment that breaks the covalent polysaccharide-protein bond. Atomic force microscopy images of the soybean pectin adsorbed to the air-water interface revealed the presence of two-dimensional pectin networks formed within the interfacial film. The soybean pectin adsorbed to the interface was confirmed to be more resistant to displacement by the competitive adsorption of the surfactant than the alkali-treated soybean pectin. The pectin moiety is expected to strengthen interfacial films mechanically, make them more resistant to surfactant-induced competitive displacement, and have beneficial effects on colloidal stability.