Gelation properties of tofu induced by different coagulants: Effects of molecular interactions between nano-sized okara dietary fiber and soybean proteins

• Nano-sized okara fiber was used to make glocono-δ-lactone and magnesium chloride tofu. • Gelation of soybean proteins behaved differently under different coagulates. • Adding nano-sized okara fiber resulted in more porous structure of the tofu. • Nano-sized okara fiber inhibited the unfolding and interactions of soybean proteins. • Tofu incorporated with nano-sized okara fiber was softer with higher yield. Gelation of soybean proteins with different coagulates as affected by okara nano-sized dietary fiber (NDF) were investigated. As compared with the MgCl 2 tofu, the tofu induced by glocono-δ-lactone was softer with higher moisture and denser microstructure. As the volumetric ratio of NDF increased, pH, viscosity, particle size, and zeta potential of the NDF soymilk steadily increased. Regardless of coagulate type, tofu proteins’ prevalence of α-helix + β-turn increased with the NDF ratio up to 40% while β-sheet + random coil decreased. At the same time, intermolecular interactions (predominate hydrophobic interaction) significantly decreased, leading to form more porous structures in the two types of tofu. Accordingly, yield and moisture of tofu increased gradually with the NDF ratio, water holding capacity increased and then decreased, hardness decreased continuously. Results suggested that NDF affected the secondary structure and intermolecular interactions of soymilk proteins, which was independent of coagulate.