Mechanism governing textural changes of low-moisture tofu induced by NaCl addition in soymilk

Abstract

This study aimed to investigate the impact of NaCl (0–1 g/100 mL) on the textural properties of calcium-coagulated low-moisture tofu (LM-tofu) and explore the underlying mechanism governing the NaCl-induced changes of relevant properties. Increasing the NaCl level in soymilk led to higher yield (134.2–192.2 g/100 g soybean) of LM-tofu with higher water content (69.2–76.7%), reduced protein (11.3–16.3%) and lipid (6.87–9.22%) levels, and enhanced water binding capacity (WBC, 4.26–6.78 g H₂O/g protein) and water holding capacity (WHC, 3.63–5.49 g H₂O/g protein) of soy proteins. Although NaCl had a minor effect on the interactions between proteins and mobilized water or tightly bound water, it significantly improved the proteins' ability to bind loosely bound water due to electrostatic interactions between the charged groups of proteins and hydrated Cl⁻ and Na⁺ ions. Moreover, the amounts of loosely bound water were highly correlated with both WBC and WHC of proteins (correlation coefficient: 0.999 and 0.995, respectively). The enhanced water binding capacity of proteins for loosely bound water due to an increased salt level resulted in LM-tofu with a less dense protein network structure, weaker strength and reduced deformation ability. This study provides insights for the development of high-calcium, soy protein-based foods to meet the growing demands for healthy and convenient plant-based snacks or meals.