Relationships between hydration number, water activity and density of aqueous sugar solutions
Relationships between hydration number, water activity and density of aqueous sugar solutions
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DOI：
10.1016/j.foodchem.2007.02.047
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发表时间：
2008-02-15
期刊：
影响因子：
8.8
通讯作者：
Mathlouthi, Mohamed
中科院分区：
文献类型：
--
作者：
Gharsallaoui, Adem;Rogé, Barbara;Mathlouthi, Mohamed
单糖的水合值（n(h)）已经用热力学、光谱和分子模拟技术研究了几十年。结果取决于所采用的技术。最可靠的值只涉及第一个水化壳，假设最大氧-氧距离低于2.8埃。随着浓度的增加，糖-糖相互作用成为优势，nh降低。假设溶质对水没有长期的结构效应，则可以通过密度测量来估计水化水（体积收缩接近9%）和散装水各自所占的体积。同样，水介质中非水合糖分子所占的体积允许在水介质中找到与固体结晶形式相当的糖密度值。另一方面，利用糖水溶液密度的文献值，可以计算出不同温度和浓度下的水化数。随着温度的升高和浓度的增加，nh的这些值明显降低。nh的减少可以解释为由于氢键寿命的差异和糖苷键周围分子折叠的差异而部分占据了潜在的水合位点（OHs）。根据nh值计算蔗糖溶液的水活度系数f(w)。结果显示与之前发现的趋势相同[Starzak， M., & Mathlouthi， M.(2006)]。蔗糖水溶液中水活度的温度依赖性。食品化学，96,346-370]，即随着摩尔浓度的增加而减少。确定了温度对水活度系数和水化数的影响。随着温度的升高，水化数减少。本文提出了利用精确的密度值计算不同浓度和温度下的水活度系数和水化数的经验关系式。这些模型首先应用于蔗糖，这是文献记载最多的糖，并应用于双糖（麦芽糖、海藻糖）和单糖（葡萄糖、果糖）。2007爱思唯尔有限公司版权所有。
Hydration numbers (n(h)) of simple sugars have been investigated for decades using thermodynamic, spectroscopic as well as molecular modelling techniques. Results were shown to depend on the technique employed. The most reliable values only concern the first hydration shell assuming a maximum oxygen-oxygen distance below 2.8 angstrom. As concentration increases, sugar-sugar interactions become preponderant and nh decreases. Assuming that no long range structuring effect is exerted by the solute on water, it is possible to estimate the volume occupied by each of hydration water (with nearly 9% volume contraction) and bulk water from density measurements. Likewise, the volume occupied by non-hydrated sugar molecules in the aqueous medium allows finding for sugar density in the aqueous medium a value comparable to that of solid crystalline form. On the other hand, using the literature values of aqueous sugar solution densities, it was possible to calculate the hydration numbers at different temperatures and concentrations. These values of nh show a noticeable decrease as temperature is raised and concentration increased. Decrease in nh can be explained assuming a partial occupation of potential hydration sites (OHs) because of differences in H-bonds lifetimes on the one hand and molecular folding around glycosidic bond on the other.Calculation of water activity coefficients (f(w)) based on nh values was made for sucrose solutions. Results show the same trend as found previously [Starzak, M., & Mathlouthi, M. (2006). Temperature dependence of water activity in aqueous solutions of sucrose. Food Chemistry, 96, 346-370] for sucrose, i.e. a decrease off, with increasing molar concentration. Temperature effect on water activity coefficients and hydration numbers is also determined. It shows a decrease in hydration number as temperature is increased. In this paper, empirical relations are proposed to calculate water activity coefficients and hydration numbers at different concentrations and temperatures by use of accurate density values. These models were first applied to sucrose, the most documented sugar and applied to disaccharides (maltose, trehalose) and monosaccharides (glucose, fructose). (c)) 2007 Elsevier Ltd. All rights reserved.