Ellwanger Felix, Fuhrmann Melanie, Karbstein Heike P, Saavedra Isusi Gabriela Itziar
Karlsruhe Institute of Technology (KIT), Institute of Process Engineering in Life Sciences, Food Process Engineering (LVT), Gotthard-Franz-Straße 3, 76131 Karlsruhe, Germany.
Thermo Fisher Scientific, Pfannkuchstr. 10-12, 76185 Karlsruhe, Germany.
Gels. 2024 Feb 29;10(3):173. doi: 10.3390/gels10030173.
High-moisture extrusion of plant proteins to create meat-like structures is a process that has met with increasing attention in the recent past. In the process, the proteins are thermomechanically stressed in the screw section of the extruder, and the resulting protein gel is structured in the attached cooling die. Various protein sources, notably soy protein isolate (SPI) and wheat gluten, are used to form gels with different networks: SPI creates a physical, non-covalent network, while gluten forms a chemical, covalent one. The food industry frequently adds weak acids to modify taste and shelf life. However, it is known that a change in pH affects the gelation behavior of proteins because the repulsive forces within and between the proteins change. The research reported here was carried out to investigate for the two proteins mentioned the influence of pH modification by the addition of citric acid and acetic acid on gel formation and the meat-like structures produced. For this purpose, materials and parameters were screened using a closed cavity rheometer, followed by extrusion trials at pH 7.36-4.14 for SPI and pH 5.83-3.37 for gluten. The resulting extrudates were analyzed optically and mechanically, and protein solubility was tested in a reducing buffer. For both protein systems, the addition of acid results in less pronounced meat-like structures. At decreasing pH, the complex viscosity of SPI increases (from 11,970 Pa·s to 40,480 Pa·s at 100 °C), the generated gel becomes stronger (strain decreased from 0.62 to 0.48 at 4.5 × 10 Pa), and the cross-linking density grows. For gluten, a decreasing pH results in altered reaction kinetics, a more deformable resulting gel (strain increased from 0.7 to 0.95 at 4.5 × 10 Pa), and a decreased cross-linking density. Solubility tests show that no additional covalent bonds are formed with SPI. With gluten, however, the polymerization reaction is inhibited, and fewer disulfide bonds are formed.
通过高水分挤压植物蛋白以形成类似肉类的结构是一个近年来受到越来越多关注的过程。在这个过程中，蛋白质在挤出机的螺杆部分受到热机械应力作用，随后在连接的冷却模头中形成蛋白质凝胶结构。各种蛋白质来源，尤其是大豆分离蛋白（SPI）和小麦面筋，被用于形成具有不同网络结构的凝胶：SPI形成物理的、非共价的网络，而面筋则形成化学的、共价的网络。食品工业经常添加弱酸来改善口感和保质期。然而，众所周知，pH值的变化会影响蛋白质的凝胶化行为，因为蛋白质内部和之间的排斥力会发生变化。本文报道的研究旨在探究添加柠檬酸和醋酸对上述两种蛋白质的pH值调节对凝胶形成及所产生的类似肉类结构的影响。为此，使用封闭腔流变仪筛选材料和参数，随后分别在pH值为7.36 - 4.14（针对SPI）和pH值为5.83 - 3.37（针对面筋）的条件下进行挤压试验。对所得挤出物进行光学和力学分析，并在还原缓冲液中测试蛋白质溶解度。对于这两种蛋白质体系，添加酸会导致类似肉类的结构不那么明显。随着pH值降低，SPI的复数粘度增加（在100°C时从11,970 Pa·s增加到40,480 Pa·s），生成的凝胶变得更强（在4.5×10 Pa时应变从0.62降低到0.48），交联密度增加。对于面筋，pH值降低会导致反应动力学改变，所得凝胶更易变形（在4.5×10 Pa时应变从0.7增加到0.95），交联密度降低。溶解度测试表明，SPI没有形成额外的共价键。然而，对于面筋，聚合反应受到抑制，形成的二硫键减少。
