Multiscale Quality Deterioration of Giant Freshwater Prawn (Macrobrachium rosenbergii) During Frozen Storage

Frozen storage is widely used to preserve shrimp products, but the multiscale mechanisms underlying quality deterioration in giant freshwater prawn remain insufficiently understood. This study investigated changes in water retention, oxidative stability, muscle structure, and protein conformation in Macrobrachium rosenbergii stored at -20 ± 2 °C for 0, 1, 3, and 5 months. Thawing and cooking losses, water-holding capacity, freshness and oxidation indices, texture, histology, low-field nuclear magnetic resonance, Fourier transform infrared spectroscopy, and intrinsic fluorescence were comprehensively evaluated. After 5 months, thawing loss increased from 8.21% to 12.51%, cooking loss increased by 55.0%, and water-holding capacity decreased from 85.45% to 68.46%. The total volatile basic nitrogen, protein carbonyl content, thiobarbituric acid reactive substances (TBARS; 0.186 to 0.528 mg MDA/kg), and myofibril fragmentation index increased progressively, while free sulfhydryl and salt-soluble protein contents declined. Shear force, hardness, cohesiveness, gumminess, and chewiness also decreased, accompanied by muscle fiber separation and an increase in white void area from 0.04% to 3.46%. Low-field nuclear magnetic resonance revealed decreases in the short-relaxation P₂b and P₂1 populations and an increase in the dominant P₂2 population, indicating relative water-population redistribution. Meanwhile, α-helix content decreased from 18.83% to 16.28%, β-sheet content increased from 25.05% to 28.22%, and maximum fluorescence intensity decreased by 31.9%. These coordinated changes suggest that prolonged frozen storage weakened the myofibrillar network through water redistribution, lipid and protein oxidation, protein fragmentation, conformational rearrangements, and tissue disruption. The findings provide a multiscale basis for developing water-retention and quality-control strategies for frozen giant freshwater prawn.