低场核磁共振法研究NaCl对肌原纤维蛋白凝胶水分分布和移动性的影响

Water-Holding Capacity in Heat-Induced Gelation of Myofibrillar Proteins as Affected by Na Cl Concentration: A Low-Field NMR Study

为解决凝胶类肉制品含盐量过高的问题,探讨了Na Cl浓度对猪肉肌原纤维蛋白热诱导凝胶水分分布和移动性的影响。分别用离心法、低场核磁共振(low-field nuclear magnetic resonance,LF-NMR)、扫描电镜研究不同Na Cl浓度下的猪肉肌原纤维蛋白凝胶保水性、水分移动性及分布状态和凝胶微观结构,并用主成分分析探讨它们之间的相关性。结果表明:随着Na Cl浓度的上升猪肉肌原纤维蛋白的保水性显著增加、加热后形成了多孔致密的结构。LF-NMR T2驰豫反演为4个峰,其加权T2分别为0.62~3.89、4.62~35.28、59.06~153.22、1 198.75~1 518.17 ms;合并后分别对应水的3种存在状态,即大分子结合水、不易流动水和自由流动水。加入Na Cl使水的移动性下降,并且使不易流动水的峰面积显著增加(P<0.05),从而增加了保水性。主成分分析结果显示不同Na Cl浓度凝胶样品在主成分评分图上表现出明显的聚类,低浓度的Na Cl在第1主成分的右端,而高浓度在第1主成分的左端,从变量评分图上也可以看出不同指标Na Cl浓度的变化情况。因此,不同Na Cl浓度下凝胶保水性的改善和不易流动水的增加明显相关。

Objective: To investigate the effect of Na Cl concentration on water distribution and mobility of pork myofibrillar protein(PMP) during heat-induced gelation in order to reduce the salt content of gel-type meat products. Methods: The water-holding capacity(WHC), T2 relaxation time, and gel microstructure were determined by centrifugation method, lowfield nuclear magnetic resonance(NMR) and scanning electron microscope(SEM), respectively. Principal component analysis(PCA) was conducted to find out the main sources of data variability and the relationship between or within samples and variables. Results: Obvious changes in WHC, T2 relaxation parameters and gel microstructure of PMP gel were observed with increasing Na Cl concentration from 0 to 0.6 mol/L. The addition of Na Cl resulted in a significant(P < 0.05) increase in the WHC of PMP heat-induced gel, which was ascribed to the more fine microstructure with increase of Na Cl concentration. The distributed water proton and NMR T2 relaxation of different contents of Na Cl after heat treatment were characterized by two minor peaks with relaxation time of 0.62–3.89 ms and 4.62–35.28 ms, a major band with relaxation time of 59.06–153.22 ms. In addition, a wide peak was also observed in the range between 1 198.75 and 1 518.17 ms. These four populations probably represent three water states, i.e., bound, immobile and bulk water according to previous literature. The position of the major peak obviously shifted to higher relaxation time with increasing Na Cl level, and the peak area fraction increased, which contributed to the increasing WHC. The addition of Na Cl resulted in gels with quite homogenous microstructure and decreased pore size after heat treatment, which was observed by SEM. The PCA results showed that the first two principal components(PC) could explain 91.23% of the total variance. The samples obtained with different Na Cl concentrations revealed a tendency to group into three clusters. The low levels of Na Cl were located in the left side of the PCA score plots, characterized low WHC, T23, P22, whereas the high contents of Na Cl were positioned in the right side and characterized the opposite attributes, and the mediate Na Cl concentration located in the middle. The correlation of these parameters was displayed in the PCA loading score plot, which displayed a strong correlation of WHC to area fraction of the major NMR relaxometry population. In conclusion, the gel functional properties are improved with increased Na Cl concentration, which is ascribed to the increase of immoblized water.