Influence of thermomechanical stresses on structural and functional changes of highly concentrated protein systems in extrusion processing

食品挤压技术和研究的最新趋势主要是针对可持续和功能性食品的开发，这些食品解决了消费者对食品产品和工艺对环境，健康和福祉的作用的日益认识。其中最有前途和增长的应用领域之一是蛋白质加工，其中植物，藻类，昆虫或乳制品蛋白质通过挤压生产肉类和乳制品的类似物或替代品。在此过程中，蛋白质受到热应力和机械应力，导致其原有分子结构发生变化。然后，通过长挤压模的流动，这些重组的蛋白质能够形成各向异性的肉状结构。挤出也被成功地用作生物反应器来生产基于蛋白质的表面活性剂、稳定剂、涂层和生物可降解薄膜。蛋白质的功能特性被认为对这些产品的质量起着重要的决定作用。其中，功能特性将由挤压过程中蛋白质的变性和聚集行为决定。因此，关于蛋白质变性和聚集动力学的信息对于更好地理解基于蛋白质的挤压产物的结构和功能化机制至关重要。过去的研究已经获得了大量关于稀模型溶液中蛋白质热诱导结构变化的有用信息。这些研究为热处理下可能发生的结构变化提供了基本信息。然而，由于更高的蛋白质浓度（> 40% w/w）和基质粘度（> 1000 Pa.s），挤压蛋白质系统与这些模型系统有很大的不同。此外，挤压过程不仅涉及蛋白质在相对较高的剪切应力（bbb10万Pa）下的热处理，还涉及蛋白质的机械处理，而且对蛋白质在这种条件下的反应行为的研究非常有限。因此，该项目第一阶段的主要目标是研究确定的挤压样条件（即高温、高剪切、短时间处理）对高浓度模型蛋白质系统（即ß-乳球蛋白）的变性和聚集行为以及由此产生的蛋白质功能的影响。在第二阶段，这些基本信息将用于表征在同向旋转双螺杆挤出机瞬态流动条件下的蛋白质修饰，我们的研究小组将使用现成的和完善的光学，流变学和数值方法来表征。除了处理条件外，模型系统的复杂性也将从单组分系统（即ß-乳球蛋白，α-乳清蛋白）增加到多组分系统（即这些蛋白质的混合物），类似于工业应用的相关条件。

Recent trends in food extrusion technology and research have been mainly directed to the development of sustainable and functional foods, which address the increased consumer awareness of the role of food products and processes on environment, health, and well–being. One of the most promising and growing application area is the processing of proteins, in which plant, algae, insect, or dairy proteins are structured to produce meat and dairy analogues or substitutes by extrusion. During this process, proteins are exposed to thermal and mechanical stresses, leading to changes of their native molecular structure. Then, through the flow in a long extrusion die, these restructured proteins are able to form anisotropic meat-like structures. Extrusion was also successfully exploited as a bioreactor to produce protein-based surfactants, stabilizers, coatings, and biodegradable films. The functional properties of proteins are considered to play a major role as quality determinant for these products. Among others, functional properties will be determined by denaturation and aggregation behavior of proteins during the extrusion process. Thus, information on the kinetics of protein denaturation and aggregation is essential to provide a better understanding of the structuring and functionalization mechanisms of protein-based, extruded products. Past research has gained a vast amount of useful information on heat-induced structural changes in proteins in dilute model solutions. These studies supply fundamental information on possible structural changes under thermal treatment. However, the extruded protein systems differ significantly from these model systems due to higher protein concentration (> 40 % w/w) and matrix viscosity (> 1000 Pa.s). Moreover, the extrusion process involves not only thermal but also mechanical treatment of the proteins at relatively high shear stresses (> 100.000 Pa), and there is only very limited number of studies on the reaction behavior of proteins at such conditions.The main goal of the first phase of this project is therefore the investigation of the influence of defined extrusion-like conditions (i.e. high temperature, high shear, short time treatment) on the denaturation and aggregation behavior of highly concentrated model protein systems (i.e. ß-lactoglobulin) and the resulting protein functionality. In phase II, this fundamental information will be used to characterize the protein modification in transient flow conditions of a co-rotating twin-screw extruder, which will be characterized by using readily available and well-established optical, rheological, and numerical methods in our research group. In addition to the processing conditions, also the complexity of the model system will be increased from single component system (i.e. ß-lactoglobulin, α-lactalbumin) to multicomponent system (i.e. mixture of these proteins) resembling the conditions relevant for the industrial applications.