Characterization of biopolymers and soy protein isolate-high-methoxyl pectin complex

Abstract This study aimed at characterizing the soy protein isolate and high-methoxyl pectin biopolymers individually, and the complexes formed by both at different proportions and pHs in order to find the most suitable pH and biopolymer ratios to food application as stabilizers. The biopolymers were evaluated through solubility, charges, turbidimetry, and optical microscopy analyses; the systems with the pair of biopolymers were analyzed through turbidimetry and optical microscopy. High-methoxyl pectin showed high solubility at all pHs investigated. The soy protein isolate showed low solubility at pH 4.5, which is close to its isoelectric point, and complete solubility at pH 11.0. The formation of complexes suggested an attractive interaction between the biopolymers, with high absorbance reading values and images of complexes from optical microscopy. These complexes were present in systems with pHs below the soy protein isolate's isoelectric point, with positive charges; the high-methoxyl pectin, however, had negative ones.