Roos Yrjö H, Potes Naritchaya
School of Food and Nutritional Sciences, University College Cork, Cork, Ireland.
J Phys Chem B. 2015 Jun 11;119(23):7077-86. doi: 10.1021/acs.jpcb.5b01593. Epub 2015 May 27.
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.
生物材料中碳水化合物和蛋白质成分的水分布及互溶性，以及它们在浓缩固体中的结构贡献仍未得到充分理解。在本研究中，使用动态力学分析（DMA）和差示扫描量热法（DSC）对牛血清白蛋白（BWP）、葡萄糖 - 果糖水溶液（GF）及其混合物进行了测量，以研究蛋白质水合水的结构弛豫、低温下的玻璃化转变以及水合水的抗塑化作用。BWP中α - 乳白蛋白和β - 乳球蛋白成分的热转变包括与含水量相关的吸热但可逆的脱水和变性，以及放热且不可逆的聚集。BWP中水合水的α弛豫出现在与含水量相关的温度下，并且在含水量降低以及存在GF的情况下，在150 - 200 K范围内增加。三元GF - BWP - 水体系中两个单独的玻璃化转变和未冻结水的各个部分导致了非耦合的α弛豫，这表明在冷冻和脱水过程中，蛋白质水合水和碳水化合物玻璃化作用在浓缩固体中具有不同作用。GF - BWP体系中BWP部分的水合水源自GF部分的平衡水吸附和玻璃化转变数据，但这为量化（i）蛋白质水合水和（ii）蛋白质 - 碳水化合物体系中的未冻结水提供了一种重要的通用方法，可用于生物材料的冷冻保存、冷冻、冻干和脱水等应用。为GF - BWP - 水体系建立的三元补充相图（状态图）可用于分析此类应用中碳水化合物和蛋白质成分之间的水分布。
