Monitoring early micro-oxidation under refrigeration: iron and oxidative markers predict quality loss in grass carp

Effective cold-chain control requires identifying early quality deterioration before overt spoilage, yet simple early indicators for chilled fish remain scarce. We evaluated whether free iron, measured by a routine assay, can predict early quality loss in refrigerated grass carp. Fillets were stored at 4 °C for 0, 24, 48 and 120 h under control and deferoxamine (DFO) chelation. Free iron, lipid and protein oxidation markers (TBARS, MDA, TCA-soluble peptides) and the myofibril fragmentation index (MFI) were quantified; proteomics and histology provided mechanistic context. Simple linear models showed that iron alone accounted for most variance in deterioration endpoints (all p < 0.0001): R² = 0.9367 (TCA), 0.9237 (TBARS), 0.8834 (MDA) and 0.8494 (MFI). Calibrated slopes (ΔY per μg/g Fe) allow estimation of downstream damage from a single iron measurement; the TBARS cut-off of 0.10 mg MDA/mg meat was predicted at ∼38 μg/g iron, within the 24-48 h consumer window. DFO lowered iron (13 % at 120 h) and mitigated oxidative injury, supporting iron modulation as a control lever. Framing free iron as an early, single-parameter sentinel links mechanism to practice: routine iron monitoring with product-specific thresholds can trigger pre-emptive interventions (tighter temperature control, food-grade chelation/acidulation, antioxidant packaging) before overt spoilage, strengthening shelf-life management in chilled fish.