Quantification of Protein Hydration, Glass Transitions, and Structural Relaxations of Aqueous Protein and Carbohydrate–Protein Systems

Abstract

Water distribution and miscibility of carbohydrate and protein components in biological materials and their structural contributions in concentrated solids are poorly understood. In the present study, structural relaxations and a glass transition of protein hydration water and antiplasticization of the hydration water at low temperatures were measured using dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) for bovine whey protein (BWP), aqueous glucose-fructose (GF), and their mixture. Thermal transitions of α-lactalbumin and β-lactoglobulin components of BWP included water-content-dependent endothermic but reversible dehydration and denaturation, and exothermic and irreversible aggregation. An α-relaxation assigned to hydration water in BWP appeared at water-content-dependent temperatures and increased to over the range of 150-200 K at decreasing water content and in the presence of GF. Two separate glass transitions and individual fractions of unfrozen water of ternary GF-BWP-water systems contributed to uncoupled α-relaxations, suggesting different roles of protein hydration water and carbohydrate vitrification in concentrated solids during freezing and dehydration. Hydration water in the BWP fraction of GF-BWP systems was derived from equilibrium water sorption and glass transition data of the GF fraction, which gave a significant universal method to quantify (i) protein hydration water and (ii) the unfrozen water in protein-carbohydrate systems for such applications as cryopreservation, freezing, lyophilization, and dehydration of biological materials. A ternary supplemented phase diagram (state diagram) established for the GF-BWP-water system can be used for the analysis of the water distribution across carbohydrate and protein components in such applications.

Changes in the Microenvironment of Nitroxide Radicals around the Glass Transition Temperature

“…Interestingly, in the case of T4-lysozyme, which does not show the discontinuity, the EPR saturation parameters of the spin-labeled side chain at position 96 indicate a smooth transition around 190 K (Figure B). Such a smooth transition of the relaxation properties around T g points to a microenvironment characterized by low fragility, and it is consistent with the broad range of T g values (160–190 K) found in hydrated protein systems (for recent reviews, see refs and ). In particular, for hydrated lysozyme, an approximate T g ∼ 180 ± 15 K was reported (see, for example, ref ), which originates from the collective motion due to the so-called main structural relaxation (α-relaxation) in hydrated proteins (for two recent reviews, see refs and ).…”

Effects of lipids on the water sorption, glass transition and structural strength of carbohydrate-protein systems

“…Bovine whey proteins have very complex protein structures and consist of β-lactoglobulin~50%, α-lactalbumin~20%, bovine serum albumin~10% as well as smaller quantities of lactoferrin and other proteins. A mix of whey proteins does not have clear representative T g (Maidannyk & Roos, 2016;Roos & Potes, 2015). Carbohydrate solids and proteins, as glass-forming food components, are often used to obtain hydrophilic encapsulant solid matrices, which have important function as continuous phase during encapsulation (Vega & Roos, 2006).…”

“…Proteins are macromolecules which interact differently with water from small carbohydrates molecules (Swenson & Cerveny, 2015). Due to hydrophobic structures, proteins have poor miscibility and molecular segregation with aqueous carbohydrates (Halle, 2004;Roos & Potes, 2015). On the other hand, the presence of lipids in dispersed phase of carbohydrate-protein system slightly decreases T g (Potes, Kerry, & Roos, 2014).…”

Glass transitions in frozen systems as influenced by molecular weight of food components

“…This result can be as a result of separate phases formed by sugars and water and high‐molecular‐weight components present in the frozen solution (Ohkuma et al., 2008; Telis & Sobral, 2002). Roos and Potes (2015) also reported that there were two separate glass transitions, including the different roles of hydrated whey protein and sugar vitrification, in the maximally freeze‐concentrated phase of ternary glucose‐fructose‐bovine milk whey protein isolate‐water (GF‐BWP‐water) systems. They observed that GF‐BWP‐water systems showed a glass transition for the sugars determined by DSC and an α‐relaxation (glass transition) at the E″ peak temperature for protein hydration water measured by DMA.…”