超高压及三聚磷酸钠质量分数对肌球蛋白凝胶保水性及热胶凝过程的影响

Effects of Ultra-high Pressure Processing and Sodium Tripolyphosphate Contents on Water-Holding Capacity of Myosin Gel and Its Heat-Induced Gelation Process

为探究超高压处理及三聚磷酸钠质量分数对肌球蛋白凝胶保水性及热胶凝过程的影响,在不同压力条件(100、200、300 MPa)下对添加不同质量分数(0%、0.15%、0.30%、0.45%)三聚磷酸钠的兔骨骼肌肌球蛋白进行25℃、9 min超高压处理后再经程序升温(1℃/min)制备凝胶,以未经超高压处理的含质量分数0.30%三聚磷酸钠的肌球蛋白为对照组,测定凝胶的保水性,并筛选出对其有显著影响的参数组合。在该条件下对蛋白的溶解度、ATP酶活力和升温过程中的蛋白二级结构含量、表面疏水性、活性巯基含量、静态流变性以及凝胶微观结构等指标进行测定。结果显示:含质量分数0.15%三聚磷酸钠的肌球蛋白经不高于200 MPa的超高压处理后,其溶解度显著下降,ATP酶活力显著上升(P<0.05);质量分数0.15%三聚磷酸钠对超高压处理诱导的肌球蛋白功能特性变化存在拮抗作用,且蛋白在升温过程中的变性、聚集受抑制,随着三聚磷酸钠质量分数升高到0.30%,拮抗作用消失,蛋白在热胶凝过程中结构充分展开,疏水基团与所包埋的巯基快速暴露,形成的凝胶结构富有弹性且致密有序,保水性显著提高(P<0.05);而300 MPa超高压处理使蛋白的ATP酶活力丧失,溶解度及热变性程度降低,分子间交联弱化,最终使凝胶保水性显著下降(P<0.05)。三聚磷酸钠通过影响蛋白的结构与理化特性,改变其热凝胶形成过程中的变性速率与交联方式,导致最终凝胶保水性发生变化。

To investigate the effect of ultra-high pressure (UHP) processing and sodium tripolyphosphate (STPP) contents on the water-holding capacity (WHC) of myosin gel and the heat-induced gelation process, rabbit Psoas major myosin dialyzed against different STPP concentrations (0%, 0.15%, 0.30% or 0.45%) were subjected to UHP treatments (25℃, 9 min) at different pressure levels (100, 200 and 300 MPa) before programmed heating (1℃/min) to form gels. Unpressurized myosin containing 0.30% STPP was set as the control. The WHC was measured to filter the parameters that had significant effects on gel properties. The protein solubility and ATPase activity and changes in the secondary structure content, surface hydrophobicity, reactive sulfhydryl group content, and rheological properties as well as the gel microstructure during heating were measured. The results indicated that the solubility of myosin containing 0.15% STPP decreased, while its ATPase activity increased significantly (P<0.05) after pressure treatments below 200 MPa, which indicates that 0.15% STPP could counteract pressure-induced changes in functional properties of myosin. The denaturation and agglomeration process were hindered as well. The counteractive effect was diminished with the increase in STPP content up to 0.30%. The protein underwent sufficient unfolding as well as rapid exposure of buried residues during gelling, which resulted in an elastic, compact and ordered gel network structure and a significant increase in WHC (P<0.05). The ATPase of myosin was inactivated under 300 MPa, and its solubility decreased as well. The extent of protein denaturation was reduced and intermolecular cross-linking was weakened. As a result, the WHC decreased significantly (P<0.05). STPP appears to affect the structure and physiochemical properties of myosin, leading to alteration in its denaturation rate and cross-linking pattern during heating and consequently change in WHC eventually.