Abstract: Objective: This study was designed to explore the change in water mobility in skin-on and skin-off pork during blast chilling and spray chilling. Methods: Ten skin-on pork loins were obtained at 2 h postmortem and each loin was cut into 4 steaks (14 cm × 10 cm × 6 cm), the skin of two of which was kept and the other two were skinless. Skin-on and skinless steaks were individually subjected to blast chilling and spray chilling. At 0.0, 1.5, 3.0, 4.5, 6.0 and 7.5 h of chilling, transverse relaxation time (T2) and magnetic resonance images (MRI) were determined by low-field nuclear magnetic resonance (LF-NMR) and sample weight was measured. Results: The A2b and P2b changed without statistical significance (P > 0.05), and the t21, A22 and P22 were significantly decreased during blast chilling (P < 0.05), while spray treatment significantly reduced A22 and P22 (P < 0.05), but it had no significant effect on A2b, P2b, t21, A21 or P21 (P > 0.05). The water mobility in skinless or skin-on pork under two chilling treatments was similar, while the evaporative loss was significantly affected by the treatments (P < 0.05). At the initial stage of blast chilling, the evaporative loss was mainly derived from free water, while it was immobilized water that contributed to the evaporative loss at the late stage. The spray chilling treatment could replace the immobilized water during the removal of heat from pork, resulting in a reduction of evaporative loss.

Key words: low-field nuclear magnetic relaxation time, low-field nuclear magnetic resonance imaging, evaporative loss, spray chilling, blast chilling