Abstract

Intermittent drying is considered as one of the alternative drying methods to save energy and improve product quality. In this study, low-field nuclear magnetic resonance (LF-NMR) has been used to evaluate the dynamics of the water mobility and distribution during the intermittent drying process. The results have shown that the first drying period of 1 hour is not effective to induce the moisture self-diffusion in the tempering period. After drying of 2 hours, the moisture transport in the tempering period became rapid and the changes reflected on T₂ curve became visible clearly. The T2 values decreased gradually during drying, which indicated the reduced water mobility. As the tempering period progresses, the T2 continuously reduced and varied, which indicated the redistribution of water molecules during the tempering period. With the prolonged tempering time, the changes in T₂ tended to be more stable, but it cannot reach equilibrium when there was concentration gradient. It was worth noting that A21 and A22 had an opposite trend during the intermittent drying process, indicating that the mobility of the bound water was increased during the intermittent drying. Effectively also when the samples were dried with the intermittent drying strategies, the vitamin C retention has increased by almost 50% relative to that of the continuous mode.

摘要

间歇干燥被认为是节约能源和提高产品质量的替代干燥方法之一。在这项研究中，低场核磁共振 (LF-NMR) 已被用于评估间歇干燥过程中水的流动性和分布的动力学。结果表明，1小时的第一次干燥期不能有效地诱导回火期的水分自扩散。干燥2小​​时后，回火期水分输送迅速，变化反映在T _{2 上}曲线变得清晰可见。T2 值在干燥过程中逐渐降低，这表明水分流动性降低。随着回火期的进行，T2不断降低和变化，表明回火期水分子重新分布。随着回火时间的延长，T ₂的变化趋于稳定，但在存在浓度梯度时不能达到平衡。值得注意的是，A21和A22在间歇干燥过程中的趋势相反，说明在间歇干燥过程中结合水的流动性增加。使用间歇干燥策略干燥样品时，与连续模式相比，维生素 C 的保留率增加了近 50%。