肌肉蛋白冻结变性介导的解冻汁液“回吸”机制

Freezing storage is the most important way for the preservation of meat, but thawing is usually accompanied with severe drip loss. At present, the research focuses on myowater outflow and the mechanism of “reabsorption” is not clear. The bovine longissimus dorsi is selected to study the effect of freezing denaturation on the protein structural and conformal characteristics, under various freezing conditions (-9 C, -18 C, -23 C, -38 C, with the aid of the electrostatic field). The study will demonstrate the mechanism of variations in protein denaturation mediated water holding capacity (WHC) and transmissibility in muscle. Low field nuclear magnetic resonance (LF-NMR) and hydrogen proton magnetic resonance imaging (MRI) are applied to monitor water state, water distribution and mobility, even the transformation of immobilized water and free water dynamically during freezing process. The variations in interaction of protein-water are also examined by measuring the intermolecular forces of muscle protein. The present study is expected to demonstrate the effects of protein renaturation and disappeared physic squeezing forces on the hydrophilicity and the capillary effects of myofibrillar protein induced by ice melting during thawing process, from multi-levels and multi-angles. Moreover, the research might elaborate the mechanism of drip reabsorbing affected by protein renaturation during freezing process, which is expected to provide theoretical basis for the control of thawing drip loss.

冻藏是原料肉贮存最主要的方式，但解冻通常伴随着严重的汁液损失。目前研究多集中在肌肉水分流出方面，而水分“回吸”的机制尚不清楚。项目以牛背最长肌（longissimus dorsi）为材料，在-9，-18，-23，-38℃条件下，耦合静电场辅助冻结处理，研究肌肉冻结变性对肌原纤维蛋白结构与肌纤维束空间构象的影响，揭示蛋白变性介导的肌肉持水性与导水性变化规律；基于低场核磁共振（LF-NMR）、H+核磁成像（MRI）及分子间作用力分析，动态监测肌肉冻结过程中水分状态、组成、分布与迁移，跟踪解冻过程中不易流动水与自由水的相互“态变”进程，阐明肌肉蛋白与水分子间互作关系；多层次多角度分析冰晶解冻消亡后肌肉蛋白复性、冰晶的物理挤压效应消失对肌原纤维蛋白亲水效应与毛细管效应的影响，揭示肌肉冻结过程中蛋白变性介导的解冻汁液“回吸”机制，为解冻汁液流失控制提供依据。

冻藏是原料肉贮藏最主要的方式，但解冻通常伴随着严重的汁液损失。目前研究多集中在肌肉水分流出方面，而水分“回吸”的机制尚不清楚。因此本项目以牛背长脊为材料，研究了-9、-18、-23及-38℃条件下肌肉冻结变性与肌肉持水性表征量变化关联，结果表明冻结温度越低，肌原纤维蛋白变性程度越低、肌肉持水性越高，说明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；对比分析了不同冻结条件下冰晶的生长与蛋白变性之间的关系，表明低温冻结下肉样冰晶形状小且致密，-23及-38℃下冻结肉样冰晶的当量直径显著小于-9与-18℃；同时SDS-PAGE电泳结果表明-9和-18℃下冻结肉样肌原纤维蛋白结构受到明显破坏，出现蛋白降解；冰晶当量直径与肌原纤维蛋白α-螺旋、β-折叠比例及二酪氨酸含量显著相关，验证了冰晶生长对蛋白结构的破坏作用，冻结温度越低，形成的冰晶直径越小，对肌原纤维蛋白结构破坏程度越小；探讨了解冻过程中蛋白-水分分子间互作关系，结果表明冻结变性的肌原纤维蛋白在解冻过程中逐渐复性，蛋白表面疏水性及蛋白溶解度结果均与之相符，肌原纤维蛋白水合力（氢键、离子键含量）也随解冻时间逐渐升高。肌肉持水性在解冻过程中逐渐升高，部分流失汁液重新被肌肉细胞吸收，出现汁液“回吸”现象。肌肉冻结过程肌肉中水凝结成冰晶，形成潜在的可流动水“库”，由于冰晶生长，肌束间隙增大，形成潜在水“渠”。同时，由于冻结导致的蛋白变性、水合能力下降，解冻后水“库”中自由水沿水“渠”迁移，形成解冻汁液流失，为肌肉冻结-解冻工艺优化及解冻汁液流失控制提供依据。