Effect of Low-Frequency Magnetic Field Assisted Freezing Time on Physicochemical Properties, Moisture Migration and Rheological Properties of Pork

This study was conducted to evaluate the effect of low-frequency alternating magnetic field assisted freezing (LF-MFF, –18 ℃) for different periods (12, 24, 36 and 48 h) on the quality of pork using fresh meat and conventional refrigerator freezing (–18 ℃, 36 h) as controls. The changes in the freezing rate, water-holding capacity, tenderness, color, pH, water migration and rheological properties of meat samples subjected to different freezing treatments were analyzed. The results indicated that compared with conventional refrigerator freezing, LF-MFF treatment at a magnetic intensity of 3 mT exhibited higher freezing rates and significantly improved pork quality (P < 0.05); among all freezing treatments, LF-MFF for 36–48 h improved the water-holding capacity, color and tenderness of pork (P < 0.05), thus maintaining better physicochemical properties. Low-field nuclear magnetic resonance (LF-NMR) results showed that the proportion of immobilized water was significantly increased and the proportion of free water was decreased after 36–48 h LF-MFF when compared with conventional refrigerator freezing (P < 0.05). Furthermore, dynamic rheological results suggested that the samples subjected to LF-MFF for 36–48 h had higher G’ values and lower degrees of protein denaturation, indicating the formation of protein gels with better viscoelasticity. The Pearson correlation analysis indicated that the changes in physicochemical properties and moisture migration of pork after different freezing treatments were significantly correlated. Therefore, LF-MFF for 36–48 h could be the optimal freezing treatment for pork, which could maintain the physicochemical properties of pork, reduce moisture migration and inhibit protein denaturation, thereby improving the quality of frozen pork.