A multi-scale evaluation of freezing damage in braised pork lean/fat tissues: Water-oil migration and quality changes

Freezing is an indispensable means of preserving meat products; however, its impact on different components of these products remains unclear. This study aimed to examine the effects of different freezing temperatures (−18 °C, −38 °C, and −80 °C) on the quality of lean and fat tissues in braised pork after reheating. Reheating frozen pork reduced water retention; in particular, moisture content decreased by approximately 2 % in lean tissues and 6 % in fat tissues across all treatment groups. Fat content showed a contrasting trend, decreasing by 4 % in lean tissues and increasing by 5 % in fat tissues. Freezing at −80 °C shortened the phase transition time by 80 % and increased the freezing rate fourfold compared to freezing at −18 °C, resulting in smaller and more uniformly distributed ice crystals. Consequently, the reheated samples in the −80 °C group exhibited the lowest porosity (5 %) and minimal fat droplet area (36 %). Magnetic resonance imaging validated that lower temperatures effectively limited moisture content and lipid migration, evidenced by a smaller gray-level frequency difference (17,050) between lean and fat tissues in the −80 °C group. Moreover, the tensile force between lean and fat tissues in the −80 °C group decreased by only approximately 7 % compared to that in fresh pork, indicating superior texture preservation. These findings provide a theoretical basis for investigating the mechanisms underlying meat quality deterioration during freezing and optimizing the cold chain management of meat products. • Freeze-reheat markedly alters the quality attributes of braised pork. • Magnetic resonance imaging can be used to visualize the migration of water and oil. • Compositional differences cause different freezing rates in lean and fat tissues. • Lower freezing temperatures better preserve the texture and microstructure.