Use of Solid Echo Sequence to Monitor Crystallization Kinetics of Mono and Di-Saccharides

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