Abstract: This study aimed to research the effect of freezing temperature on beef myofibrillar protein denaturation and water-holding capacity (WHC), and to explore the correlation between myofibrillar protein denaturation and WHC. Beef Longissimus dorsi frozen at ?9, ?18, ?23 and ?38 ℃ were tested. Myofibrillar protein denaturation was investigated by the determination of sulfrydryl content, protein solubility, Ca2+-adenosine triphosphatase (ATPase) activity and protein thermal stability. WHC was evaluated by thawing loss and pressing loss. In addition, muscle water distribution was analyzed by low field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI). Color difference and shear force were also measured after thawing at 4 ℃. Results demonstrated that samples frozen at ?23 and ?38 ℃ showed lower degree of protein denaturation, higher protein solubility, Ca2+-ATPase activity and total denaturation enthalpy than those frozen at ?9 and ?18 ℃ (P < 0.05). In addition, L* value, b* value and shear force in thawed samples, thawing loss and pressing loss dropped significantly compared to those frozen at ?9 and ?18 ℃ (P < 0.05). LF-NMR and MRI analyses consistently showed that freezing at ?23 and ?38 ℃ resulted in higher WHC than at ?9 and ?18 ℃. Furthermore, the physicochemical properties (solubility, Ca2＋-ATPase activity, sulfrydryl content and total denaturation enthalpy) as well as L* value, b* value and shear force of beef myofibrillar protein were highly significantly correlated with WHC (P < 0.01). Consequently, myofibrillar protein denaturation during beef freezing had a significant impact on WHC, causing color deterioration, reduced tenderness and juice loss after thaw.

Key words: freezing temperature, beef, myofibrillar protein denaturation, water-holding capacity