超声处理对蛋清蛋白结构性质及蛋清液起泡性的影响

研究脉冲式超声处理对蛋清液拉曼光谱、内源性荧光光谱、静态流变学性质、粒径和理化结构的影响，结合起泡性的变化进行相关性分析。研究发现，超声处理能够改变蛋清蛋白二硫键构象，降低蛋清液黏度，减少总巯基含量，对无规卷曲、β-转角含量和酪氨酸残基峰强比（I850/I830）影响较小，蛋清液依旧为假塑性流体。在超声处理15 min内，蛋清蛋白质粒径、表面巯基含量、热变性焓（ΔH）、α-螺旋和β-折叠含量逐渐减少，内源性荧光强度和表面疏水性逐渐增强，色氨酸残基趋向于“暴露的”展开形式；起泡性得到改善，且泡沫体积小，呈均匀紧密的排列，泡沫稳定性小幅降低。随着超声时间的延长，β-折叠含量继续降低，粒径、表面巯基含量、ΔH、α-螺旋含量、色氨酸残基峰强比（I1 363/I1 338）、内源性荧光强度和表面疏水性呈现不同的变化趋势，起泡性逐渐降低，但泡沫稳定性有所升高。相关性分析表明，起泡性与I1 363/I1 338、表面疏水性呈正相关，与ΔH、平均粒径、α-螺旋含量和表面巯基含量呈负相关，泡沫稳定性与表面疏水性呈负相关。

Effect of Ultrasonic Treatment on Protein Structure and Physicochemical and Foaming Properties of Liquid Egg White

The effect of pulsed ultrasonic treatment on the foaming properties, Raman spectroscopy, endogenous fluorescence spectroscopy, static rheological properties, particle size, physicochemical properties and structural characteristics of liquid egg white (LEW) was investigated. Correlation analysis was also conducted. The results showed that the disulfide bond conformation of egg white protein (EWP) was changed by ultrasonic treatment, and the viscosity and total sulfhydryl group content of LEW were decreased accordingly. LEW was still a pseudoplastic fluid after ultrasonic treatment. The particle size, surface sulfhydryl content, thermal denaturation enthalpy (ΔH) and α-helix and β-sheet contents of EWP gradually decreased with increasing ultrasonic treatment time up to 15 min, whereas the endogenous fluorescence intensity and surface hydrophobicity increased. The tryptophan residues tended to be exposed on the protein surface. Meanwhile, the foaming capacity was gradually improved, and the foam stability was reduced marginally. The micromorphology of the foam was smaller and more evenly and closely arranged after ultrasonic treatment. The content of β-sheet continued to decrease with increasing ultrasonic time, whereas the opposite was observed for particle size, surface sulfhydryl content, ΔH, α-helix content, intensity ratio of tryptophan residues (I1 363/I1 338) ratio, endogenous fluorescence intensity and surface hydrophobicity. Meanwhile, foaming capacity gradually decreased, while foam stability increased. The correlation analysis showed that foam capacity was positively correlated with I1 363/I1 338 ratio and surface hydrophobicity, and negatively correlated with surface sulfhydryl content, ΔH, average particle size, and α-helix content. In addition, foam stability was negatively correlated with surface hydrophobicity.