关键词: 牛肉；极限pH值；肌浆蛋白；理化特性；结构特性

Abstract: This study focused on sarcoplasmic proteins from three types of beef with different ultimate pH (normal, intermediate, and high pHu). The sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) patterns, secondary structure, ultraviolet (UV) spectral characteristics, fluorescence spectral characteristics, turbidity, particle size and zeta potential, surface hydrophobicity, solubility, thiol content and emulsifying properties were analyzed to explore the mechanism underlying the differences in physicochemical properties and structural characteristics of these sarcoplasmic proteins. Results indicated no significant compositional differences among the three sarcoplasmic proteins, but systematic variations existed in molecular conformation. The normal pHu beef sarcoplasmic protein had the highest β-sheet content, surface hydrophobicity and UV absorbance value, while the fluorescence intensity, absolute value of zeta potential, and sulfhydryl content were the lowest. This indicates that its molecular conformation was extended, the hydrophobic region was exposed, the electrostatic repulsion was weak, and the protein was prone to aggregation, resulting in the lowest solubility, highest turbidity, and largest particle size. In contrast, the intermediate pHu and high pHu beef sarcoplasmic proteins had higher α-helix and flexible structure contents, greater fluorescence intensity, higher sulfhydryl content, larger absolute value of zeta potential, lower hydrophobicity, and a more compact and ordered molecular conformation, thus resulting in higher solubility and lower turbidity and particle size. These structural changes led to differences in functional properties. The high pHu beef sarcoplasmic protein exhibited the best emulsifying activity due to its structural characteristics that facilitated rapid interface adsorption, whereas the intermediate pHu beef sarcoplasmic protein had a stable conformation and could form a more solid interface membrane, thus possessing the optimal emulsifying stability. In summary, the pHu of beef is a key intrinsic factor determining the conformation and functional properties of its sarcoplasmic proteins. This finding helps to scientifically select and match raw meat for different product-specific requirements in meat processing.

Key words: beef; ultimate pH; sarcoplasmic protein; physicochemical properties; structural characteristics