不同冻结温度下牛肉的肌原纤维蛋白变性与肌肉持水性

为明确冷冻温度对牛肉肌原纤维蛋白变性和肌肉持水性（water-holding capacity，WHC）的影响、探讨肌 原纤维蛋白变性与WHC的相关性。以牛背最长肌作实验材料，探究－9、－18、－23、－38 ℃下冻结后肌原纤维 蛋白理化特性和牛肉WHC。通过测定巯基含量、蛋白质溶解度、Ca2＋-三磷酸腺苷酶（adenosine triphosphatase， ATPase）活力及蛋白质热稳定性考察牛肉冻结后肌原纤维蛋白变性情况，利用解冻汁液流失与加压失水率指标衡 量牛肉WHC，采用低场核磁共振（low field-nuclear magnetic resonance，LF-NMR）波谱和磁共振成像（magnetic resonance imaging，MRI）技术对比分析了肌肉水分分布情况，并于4 ℃解冻后测定了色差与剪切力。结果表明： －23 ℃与－38 ℃下冻结试样较－9 ℃与－18 ℃肌原纤维蛋白变性程度小：－23 ℃与－38 ℃下冻结试样蛋白质溶解 度、Ca2＋-ATPase活力、巯基含量和总变性焓相比－9 ℃与－18 ℃实验组较高（P＜0.05）。－23 ℃与－38 ℃下冻 结牛肉解冻后L*值、b*值、剪切力、解冻汁液流失和加压失水率显著低于－9 ℃与－18 ℃（P＜0.05）。LF-NMR 及MRI结果相互佐证了肉样在－23 ℃与－38 ℃冻结下肌肉WHC高于－9 ℃与－18 ℃的实验结果。肌原纤维蛋白理 化特性（蛋白质溶解度、Ca2＋-ATPase活力、巯基含量、总变性焓）与WHC（解冻汁液流失率、加压失水率）均呈 极显著相关（P＜0.01），L*、b*值及剪切力亦与WHC存在极显著相关（P＜0.01）。相关性分析结果验证了牛肉冻结 过程中肌原纤维蛋白变性对肌肉持水性存在显著影响，进而导致牛肉解冻后出现肉色劣变、嫩度下降及汁液流失。

Myofibrillar Protein Denaturation and Water-Holding Capacity of Beef Frozen at Different Temperatures

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.