Concentration-dependent changes in the reaction behavior of whey proteins: Diffusion-controlled or transition state-controlled reactions?. (September 2021)

• Record Type: Journal Article
• Authors: Quevedo, Maria; Karbstein, Heike P.; Emin, M. Azad
• Is Part Of: Food hydrocolloids. Volume 118(2021)
• Publication Date: 2021-09
• Subjects: Whey proteins -- Denaturation -- Diffusion -- Unfolding -- Aggregation -- Transition-state -- Thermomechanical treatment -- Collision theory; Hydrocolloids -- Periodicals; Food additives -- Periodicals; Colloïdes -- Périodiques; Aliments -- Additifs -- Périodiques; Colloids; Food additives; Periodicals; Electronic journals; 664.06
• DOI: 10.1016/j.foodhyd.2021.106745
• Languages: English
• ISSNs: 0268-005X

Abstract

Abstract: The denaturation of whey proteins can be used in a controlled manner to design protein-based products with new specific structures or functionalities e.g., meat and dairy analogues, as well as protein-based emulsifiers and thickeners with specific functionalities. For this, the influence of thermal and/or mechanical treatment, and milieu conditions including the protein concentration, on the denaturation reaction must be determined. Previous results of whey protein denaturation at concentrations above 50% suggested a strong change in the reaction behavior of whey proteins compared to more dilute conditions (concentration < 20%). Therefore, in this study the reaction behavior of whey proteins at a broad range of concentrations 17–70% after thermal and mechanical treatment was investigated. The results of this study suggest that the reaction limiting step depends on the concentration of the system. Calculations of the collision rate as a function of protein concentration indicate that the collision theory can only be applied to explain the denaturation reaction mechanisms for certain conditions. At dilute- and semi-dilute conditions, since the protein molecules are quasi-isolated and unentangled, the diffusion of molecules controls the aggregation step, and consequently the denaturation reaction is a diffusion-limited reaction. In contrast at concentrated conditions, the protein molecules are entangled, which can hinder the unfolding of the globular structure and consequently the formation of a transition-state becomes the limiting step. Graphical abstract: Image 1 Highlights: Whey protein denaturation and its limiting steps depend on the protein concentration. The critical concentration for protein entanglement was determined. Below 40% the diffusion of molecules controls the aggregation step. At higher conditions, protein entanglements hinder the unfolding step. Above 60% the formation of a transition-state becomes the limiting step.