Crystallization is an important quality parameter that can significantly affect consumer acceptability and perceived quality of the products. Especially in high sugar products, controlling crystallization is a challenge. In this study, the goal is to explain the mechanism of crystallization kinetics of common simple sugars that are mostly used in food processes, namely glucose, fructose, lactose, sucrose as well as a low-calorie rare sugar, allulose. The crystallization process was monitored by Time-domain Nuclear Magnetic Resonance (NMR) techniques. Solid Echo (SE) pulse sequence was used for the measurements. Measurements were recorded as the temperature of high sugar content solutions decreased from 50 to 28 °C. The acquired data were fit to a kinetic model. The crystallization rate of disaccharides (sucrose and lactose) were found to be much faster than the monosaccharides as expected. However, the crystallization rate of glucose and fructose was much slower than their isomer, allulose. Position of the hydroxyl group, as well as mutarotation vs. crystallization reaction rate, was hypothesized to be the determinant on the crystallization behavior. The results were also supported by moisture content, optical microscopy, and X-ray diffraction analysis. Time-domain NMR by SE sequence was suggested as a practical, quick means as a quality control technique to predict crystallization rate and crystal content of high sugar products.

Graphical abstract

中文翻译：

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使用固体回波序列监测单糖和双糖的结晶动力学

结晶度是一个重要的质量参数，可以显着影响消费者对产品的接受度和感知质量。特别是在高糖产品中，控制结晶是一个挑战。在这项研究中，目的是解释主要用于食品加工的常见单糖的结晶动力学机制，即葡萄糖、果糖、乳糖、蔗糖以及低热量的稀有糖，阿洛酮糖。结晶过程由时域核磁共振（NMR）技术监测。固体回波 (SE) 脉冲序列用于测量。当高糖含量溶液的温度从 50°C 降至 28°C 时记录测量值。获得的数据适合动力学模型。发现二糖（蔗糖和乳糖）的结晶速率比预期的单糖快得多。然而，葡萄糖和果糖的结晶速率比它们的异构体阿洛酮糖慢得多。羟基的位置以及变旋与结晶反应速率的关系被假设为结晶行为的决定因素。结果也得到了水分含量、光学显微镜和 X 射线衍射分析的支持。SE 序列的时域 NMR 被建议作为一种实用、快速的方法作为质量控制技术来预测高糖产品的结晶速率和晶体含量。以及变旋与结晶反应速率，被假设是结晶行为的决定因素。结果也得到了水分含量、光学显微镜和 X 射线衍射分析的支持。SE 序列的时域 NMR 被建议作为一种实用、快速的方法作为质量控制技术来预测高糖产品的结晶速率和晶体含量。以及变旋与结晶反应速率，被假设是结晶行为的决定因素。结果也得到了水分含量、光学显微镜和 X 射线衍射分析的支持。SE 序列的时域 NMR 被建议作为一种实用、快速的方法作为质量控制技术来预测高糖产品的结晶速率和晶体含量。

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