Effects of supercooling, sub−freezing, and deep−freezing pre−cooling on color, pH, shear force, sensory quality, and myofibrillar protein properties of beef during expanded polystyrene−based distribution

This study evaluated the effects of different pre-cooling phase states on beef quality during e-commerce distribution. Beef steaks were subjected to four treatments: 4 °C (CK), - 0.5 °C (supercooling), - 5 °C (sub-freezing), and - 18 °C (deep-freezing), followed by 48 h of EPS-based passive distribution at 25 °C and subsequent storage at 4 °C. Changes in color, pH, shear force, sensory quality, myoglobin oxidation, myofibril fragmentation index (MFI), and the biochemical and conformational properties of myofibrillar proteins (MPs) were analyzed. The results showed that pre-cooling temperature significantly affected beef quality during distribution and storage. Although deep-freezing (- 18 °C) provided better initial color protection, the associated ice crystal damage likely intensified moisture exudation, myoglobin oxidation, and protein oxidation during the subsequent temperature rise and refrigerated storage, which together may have contributed to structural disruption and faster quality deterioration. As a result, the - 18 °C and - 5 °C groups showed faster deterioration in color, texture, and sensory quality, accompanied by higher MetMb content, carbonyl content, surface hydrophobicity, and β - sheet proportion, as well as lower protein solubility. In contrast, the - 0.5 °C supercooling treatment showed the best overall performance by maintaining higher redness, better texture stability, and a longer period of sensory acceptability. At the molecular level, supercooling delayed MP oxidation, reduced hydrophobic group exposure and structural rearrangement, and better preserved the ordered secondary structure of proteins. Overall, - 0.5 °C supercooling was more effective than sub-freezing and deep-freezing in maintaining beef quality during EPS-based distribution.