Effects of ice temperature or chilled storage on quality and moisture migration of yak meat

In order to explore the storage quality of yak meat from the molecular level, this study evaluated the effects of ice temperature (-2 ℃) and chilled (0 ℃) storage on the change of sensory quality, malondialdehyde content, the total bacterial number, and color value of fresh yak meat. Low-field nuclear magnetic resonance (LF-NMR) was used to study the moisture migration in yak meat during storage. Fourier transform infrared spectroscopy (FTIR) was applied to investigate the structural protein changes in yak meat during storage. The results showed that the sensory quality of fresh yak meat after 24 days of storage at -2 ℃ was still kept the secondary freshness according to Chinese national standard, the total bacterial number was 5.12 lg(CFU/g). But the sensory quality of fresh yak meat after 18 days of storage at 0°C reached the secondary freshness with the total bacterial number of 5.25 lg(CFU/g).The quality deterioration was found in yak meat after 24 days of storage at 0 ℃, the total bacterial number reached 6.28 lg(CFU/g). The color value (a* value) of fresh yak meat firstly rose and then decreased, but the color value of yak meat stored at -2 ℃ exhibited fewer changes than test samples stored at 0 ℃. The results showed that the content of malondialdehyde in fresh yak beef increased significantly with the prolongation of storage time. The malondialdehyde content in yak meat stored at 0 °C increased faster than that stored at -2 ℃. Those data indicated that the ice temperature (-2 ℃) has a better efficacy of storage and preservation for fresh yak meat. At the same time, the combined water pT21 in chilled fresh yak meat was similar to that of pT22 under the different storage conditions, and the difference was not significant (P>0.05). The non-flowing water pT23 in fresh yak meat stored at -2℃ fluctuated less than that stored at 0 ℃. The change of free water pT24 was opposite to that of non-flowing water. Under different storage conditions, the relaxation times of yak meat T21, T22, and T24 were corresponded to the combined water and free water, respectively. The combined water in yak meat stored at -2 ℃showed fewer changes than that of samples at 0℃. This indicated that ice temperature (-2 ℃) storage were more conducive to maintaining the interaction of water molecules with other biological macromolecules. These data indirectly revealed that the ice temperature (-2℃) storage has a greater storage and preservation effect on the fresh yak meat. The comprehensive analysis showed that compared with refrigeration conditions, the combination of water and protein molecular of the yak beef was more stable than that of samples under ice temperature conditions, which was more favorable for maintaining physiological and biochemical parameters for meat quality determination. Therefore, the ice temperature storage used for meat preservation was better than the chilled storage. The experiment provided a new reference method in the research of the storage and preservation of meat.