Protein-water interactions and textural characteristics of low-moisture tofu as affected by sodium chloride and star anise extract

To explore the feasibility of simplifying the process of producing flavored low-moisture tofu (LMT) to satisfy growing consumer demand for high-quality plant-based foods rich in protein, this research aimed to investigate protein-water interactions and textural characteristics of high calcium LMT as affected by the addition of table salt (0.75% w/v) and star anise (SA) extract (4.44% or 6.67% v/v; imparting mild or moderate licorice taste in LMT) in soymilk. Adding table salt in soymilk with or without SA resulted in an average of 22.6–23.9% increase in the water binding capacity of protein (WBC_pro) in LMT, attributing to the enhanced capability of soy protein to bind water molecules presumably via electrostatic interactions with hydrated Na⁺ and Cl⁻ ions. Consequently, significant (p < 0.05) increases in the yield and moisture levels were found in salted LMT with or without SA, corresponding to a significant decrease of protein concentration (14.75 ± 0.13%– 14.86 ± 0.14% vs. 17.32 ± 0.23%; w/w), reduced density of the protein network structure and thereby an overall decline in the strength (e.g., hardness, chewiness, failure stress, stiffness, etc.) of LMT high in calcium (> 240 mg/100 g). The further addition of SA besides table salt did not significantly influence the composition, WBC_pro, protein network structure, and textural characteristics of LMT. This research indicates the great potential to simplify the production of flavored LMT without dehydrating and brining, providing a new approach to produce a high calcium plant-based food possibly used as a meat analogue or vegetarian alternative.