Objective This study aimed to develop a food-grade liquid cryoprotectant formulation suitable for aquatic products and validate its efficacy in rapid freezing of tilapia, providing a foundation for advancing liquid rapid-freezing technology in aquatic food preservation.

Method Food-grade alcohols (ethanol, propylene glycol), salts (NaCl, CaCl₂), sugars (dextran, trehalose), and betaine were selected as components of the liquid cryoprotectant. The freezing point and viscosity were used as evaluation indices. A multi-component cryoprotectant formulation was optimized through single-factor experiments combined with Box-Behnken response surface methodology. Comparative Analysis of immersion freezing (IF) under optimal cryoprotective solution formulation with air freezing (AF), blast freezing (BF), and liquid nitrogen freezing (LNF) for tilapia preservation. Physicochemical indices, including water holding capacity (WHC), pH, total volatile basic nitrogen (TVB-N), thiobarbituric acid reactive substances (TBARS), color, and texture properties, were analyzed. The effects of the four freezing methods on tilapia quality were further investigated using low-field nuclear magnetic resonance (LF-NMR) for water distribution analysis and microscopic/SEM observations of muscle microstructure.

Result The optimal cryoprotectant formulation comprised 20.00% ethanol, 10.19% propylene glycol, 8.00% NaCl, and 15.00% betaine (mass percentages relative to total solution). This formulation exhibited a low freezing point (-67.02℃) and low viscosity (14.09 mPa·s at -30℃). Freezing rate analysis revealed that the IF group achieved significantly faster freezing than AF, BF, and LNF groups (P < 0.05). Physicochemical evaluations demonstrated that the IF group exhibited superior WHC, TVB-N, TBARS, and texture properties compared to AF and BF groups (P < 0.05), with no significant differences from the LNF group (P > 0.05). Microscopic and SEM imaging confirmed that the IF group maintained the most intact muscle fiber structure, with small and uniformly distributed intracellular ice crystals. LF-NMR analysis indicated significantly higher proportions of immobilized water in the IF group compared to AF and BF groups (P < 0.05).

Conclusion A multi-component liquid cryoprotectant composed of ethanol, propylene glycol, NaCl, and betaine was successfully developed. Application of this cryoprotectant in rapid freezing preserved tilapia quality effectively, yielding thawed fish with milky-white flesh, enhanced water retention, minimal drip loss, dense tissue structure, and delayed protein denaturation and lipid oxidation.