Abstract: In order to investigate the change of water state in normal beef and dark, firm and dry (DFD) beef during postmortem aging and its effect on water-holding capacity (WHC), the change of water state in normal beef and DFD beef Longissimus dorsi aged for 3, 7, 14 and 21 days postmortem was explored using low-field nuclear magnetic resonance (LF-NMR), and the reason for the difference in WHC between normal and DFD beef was analyzed by using histological analyses such as sarcomere length and the percentage of extracellular space. The results showed that water-holding capacity revealed a decreasing trend during postmortem aging in both normal beef and DFD beef, and DFD beef had significantly higher WHC than normal beef (P < 0.05). The freedom degree of bound water, immobilized water and free water was lower in DFD beef, which had a higher content of bound water when compared with normal beef The sarcomere length of DFD beef was significantly lower than that of normal beef (P < 0.05), leading to narrow storage space in sarcomere and consequently reduced degree of freedom of water. Moreover, the muscular cells of DFD beef remained intact and showed reduced water evaporation during aging so that DFD beef could well maintain its water-holding capacity. The results of this study clarified the change of water state in beef during postmortem aging and uncovered the reason for better water-holding capacity in DFD beef during aging by using water state and histological analysis, which will provide a theoretical guidance for improving the water-holding capacity of beef.

Key words: DFD beef, aging, low-field nuclear magnetic resonance, sarcomere length, extracellular space