Differential freezing responses in gill side flesh vs. collar flesh of bighead carp (Aristichthys nobilis) head: the role of ice crystal formation in protein and lipid deterioration

To preserve the structure and quality of critical edible regions in frozen bighead carp (BHC) heads. Air freezing (AF, −30 °C), composite immersion freezing (CIF, −30 °C), and liquid nitrogen spray freezing (LNSF, −90 °C) were compared for the effects on the water status, ice morphology, microstructure, protein characteristics, and lipid oxidation of gill side flesh (GSF) and collar flesh (CF). Dendritic ice crystals formed in AF samples, fracturing collagen fibers. CIF and LNSF promoted spherical ice, preserving adipocytes and collagen structure. LNSF reduced water migration, maintained the α-helix content (27.68%), and suppressed protein unfolding in GSF, resulting in smoother and intact surfaces of the muscle bundles. LNSF treated CF showed the lowest values of malondialdehyde (0.27 mg/kg), acid value (1.53 mg/g), and peroxide value (5.01 mmol/kg). Overall, the quality of BHC heads was preserved by LNSF at −90 °C. This study establishes freezing technological for frozen fish heads. • Collar flesh (CF) more susceptible to ice crystal damage than gill side flesh (GSF). • Collar flesh quality is a key indicator for evaluating fish head quality. • Loss of integrity in CF collagen fibers leads to fat cell puncture and moisture loss. • Small, round ice crystals from ultra-fast freezing preserved GSF protein integrity.