通过与钙的冷凝胶化制备了乳清蛋白分离物(WPI)的模型凝胶。通过在该方法的不同步骤添加游离半胱氨酸残基(Cys)来修饰该系统。然后将获得的WPI冷固化凝胶在90°C下进行热处理。首先,通过原子力显微镜(AFM)和红外光谱(ATR-FTIR)研究了Cys添加对WPI热诱导聚集的影响,通过AFM观察到Cys对冷凝胶化的影响,共聚焦激光扫描显微镜(CLSM)和振荡流变学(振幅扫描)。最后通过几种技术研究了加热对WPI冷固化凝胶的微观结构和粘弹性能的影响,包括DSC,ATR-FTIR,CLSM,cryo-SEM,和流变测量(温度扫描)。当在冷凝胶化的第一步中添加时,Cys修饰的热诱导WPI聚集,导致形成分形维数(Df)为2.8的更致密的凝胶网络。然而,在冷凝胶化的第二步骤期间Cys的添加导致形成高度支化的WPI簇,并且观察到更松散的凝胶网络(Df=2.4)。在这方面,讨论了振荡流变学和“Kraus模型”确定WPI冷固化凝胶Df的用途和局限性。通过加热不可逆地改变了WPI冷固化凝胶的粘弹性和微观结构。凝胶更硬,更脆,热处理后更粗糙。新的二硫键和钙桥形成,以及H-键合的β-折叠,都有助于最终凝胶网络结构的形成。
A model gel of whey protein isolate (WPI) was prepared by cold gelation with calcium. This system was modified by the addition of free cysteine residues (Cys) at different steps of the process. The WPI cold-set gels obtained were then subjected to heat treatment at 90°C. First, the effect of Cys addition on the heat-induced aggregation of WPI was studied through Atomic Force Microscopy (AFM) and infrared spectroscopy (ATR-FTIR), while Cys\' effect on cold gelation was observed by AFM, Confocal Laser Scanning Microscopy (CLSM) and oscillatory rheology (amplitude sweeps). The impact of heating on the microstructure and the viscoelastic properties of the WPI cold-set gels were finally investigated through several techniques, including DSC, ATR-FTIR, CLSM, cryo-SEM, and rheological measurements (temperature sweeps). When added during the first step of cold gelation, Cys modified heat-induced aggregation of WPI, resulting in the formation of a denser gel network with a fractal dimension (Df) of 2.8. However, the addition of Cys during the second step of cold gelation led to the formation of highly branched clusters of WPI and a looser gel network was observed (Df = 2.4). In this regard, the use and limitations of oscillatory rheology and the \"Kraus model\" to determine the Df of WPI cold-set gels was discussed. The viscoelastic properties and the microstructure of the WPI cold-set gels were irreversibly modified by heating. Gels were stiffer, more brittle, and coarser after heat treatment. New disulfide bonds and calcium bridges formed, as well as H-bonded β-sheets, all contributing to the formation of the final gel network structure.