Effect of ultrasound treatment on thawing process of frozen tofu prepared with different salt coagulants

Abstract

This study investigated the effects of ultrasound-assisted water thawing (UWT) at different power levels (0, 100, 150, 200, and 250 W) on the thawing rate and gel properties of frozen tofu made using three different salt coagulants (CaCl₂, CaSO₄, and MgCl₂). Tofu produced with CaCl₂ and CaSO₄ elicited gel structures with dense and homogeneous networks, while that with MgCl₂ had rough pores and irregular networks. UWT treatment significantly decreased thawing time by 30.9-53.5% compared to the control. Water holding capacity and scanning electron microscopy analyses demonstrated that UWT-100, UWT-150, and UWT-200 should be used to increase the amount of fixed water for CaCl₂, CaSO₄, and MgCl₂. These findings suggest that appropriate ultrasonic treatment could improve the water retention capacity of the tofu network and make the gel network structure more compact. Additionally, protein structural analysis showed a decrease in the exposure of hydrophobic groups and reduced protein denaturation when tofu prepared with all the coagulants were thawed with UWT energies of 100-200 W ultrasonication. These findings offer theoretical support for improving the frozen tofu thawing process while ensuring optimal final product quality.

Keywords: Coagulant; Thawing rate; Tofu; Ultrasound; Water transfer.