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针对可持续和功能性食品的开发，这解决了消费者对食品和食品加工对环境，健康和福祉的作用的认识。最有前途和不断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被结构化以通过挤出生产肉类和乳制品类似物或替代品。在此过程中，蛋白质暴露于热应力和机械应力，导致其天然分子结构的变化。然后，通过长挤出模头中的流动，这些重组蛋白能够形成各向异性的肉状结构。挤出也被成功地开发为生物反应器，以生产蛋白质为基础的表面活性剂，稳定剂，涂料和可生物降解的薄膜。蛋白质的功能特性被认为是这些产品的质量决定因素。其中，功能特性将由蛋白质在挤出过程中的变性和聚集行为决定。因此，关于蛋白质变性和聚集的动力学的信息对于提供对基于蛋白质的挤出产品的结构化和功能化机制的更好理解是必不可少的。 过去的研究已经获得了大量有用的信息，在稀模型溶液中的蛋白质的热诱导结构变化。这些研究为热处理下可能的结构变化提供了基本信息。然而，由于较高的蛋白质浓度（> 40%w/w）和基质粘度（> 1000 Pa.s），挤出的蛋白质系统与这些模型系统显著不同。此外，挤出过程不仅涉及蛋白质的热处理，而且涉及在相对高的剪切应力下的机械处理（> 100.000 Pa），并且只有非常有限数量的关于蛋白质在这种条件下的反应行为的研究。因此，本项目第一阶段的主要目标是研究限定的挤出样条件的影响本发明的目的在于提供一种用于高浓度模型蛋白质系统（即β-乳球蛋白）的变性和聚集行为的方法（即高温、高剪切、短时间处理）以及所得的蛋白质功能性。在第二阶段，这一基本信息将被用来表征蛋白质修饰在瞬态流动条件下的同向旋转双螺杆挤出机，这将是其特征在于使用现成的和完善的光学，流变学和数值方法在我们的研究小组。除了加工条件外，模型系统的复杂性也将从单组分系统（即β-乳球蛋白、α-乳白蛋白）增加到多组分系统（即这些蛋白质的混合物），类似于工业应用相关的条件。

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.