Effects of Freezing Temperature on the Quality of Braised Pork Belly

In this study, braised pork belly was frozen at different temperatures (−18, −38, and −80 ℃), and the resulting quality changes were evaluated in terms of water-holding capacity, texture, color, moisture distribution and microstructure. The results showed that freezing led to a significant reduction in the moisture content of braised pork belly. After thawing, the water-holding capacity of the −80 ℃ frozen group was 86.49%, which was significantly higher than that of the −18 ℃ and −38 ℃ groups (P < 0.05), and was close to that of the fresh sample (89.30%). The results of low-field nuclear magnetic resonance (LF-NMR) confirmed that freezing at low temperatures delayed the migration of immobilized water (T₂₂) to free water (T₂₃), thereby maintaining the water-holding capacity of the product. In terms of texture, the hardness, springiness and chewiness of the lean part were significantly lower than those of the control group (P < 0.05), while those of the fat part showed an increasing trend. The texture quality of the −80 ℃ frozen group was significantly better than that of the other groups (P < 0.05). Microstructural observations revealed that freezing at −80 ℃ effectively inhibited the growth of ice crystals and reduced damage to muscle fiber structure (P < 0.05). The porosity between muscle fiber bundles was only 6.47%, significantly lower than that of the −18 ℃ (11.67%) and −38 ℃ (9.25%) groups. After thawing, the fat droplets were more uniformly distributed in the −80 ℃ group, with a smaller relative area of 30.53% compared with the −18 ℃ (39.74%) and −38 ℃ (32.67%) groups. The b* value of the lean layer and the L* value of the fat layer in the −18 ℃ freezing group were significantly higher than those in the other treatment groups (P < 0.05). Different freezing temperatures had no significant effect on the a* value of braised pork belly or the b* value of the fat layer (P > 0.05). In conclusion, freezing at −80 ℃ was more effective in preserving the water-holding capacity and textural properties of braised pork belly, thereby maintaining its overall quality.