Analysis of Moisture Changes in Flos lonicerae at Different Flowering Stages during Infrared Drying Using Low-field NMR
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Abstract:
Changes in water distribution and water states in Flos lonicerae during infrared drying were assessed at three different flowering stages (three green period, large white period, and golden flowering period). The three F. lonicerae samples were subjected to far-infrared radiation at 45 ℃, and low field-nuclear magnetic resonance (LF-NMR) spectroscopy was employed to evaluate differences in water mobility and distribution. Three water states – bound water, immobilized water, and free water – were detected in F. lonicerae samples at different flowering stages, with volume fraction decreasing in the order: immobilized water > bound water > free water. The proportions of free water and bound water in the F. lonicerae sample at the three green stage were higher than those in the F. lonicerae samples at the big white and whole flowering stages, and the immobilized water content of the F. lonicerae sample at the three green stage was lower than those of the samples at the big white and whole flowering stages. During the drying process, different forms of water also exhibited different patterns of change; the immobilized water content decreased gradually, while the bound water content decreased at first and then increased. The drying process changed the internal water distribution and water content of the F. lonicerae samples, and interconversion between different forms of water occurred. The fluidity of the bound water increased during the initial period of drying, before decreasing during the final stages of the drying process. However, the fluidity of the bound water of the sample at the large white stage continued to decrease throughout the drying process. During the drying process, the water content of F. lonicerae was highly correlated with the peak area of immobilized water and the total peak area (R2 > 0.9). Thus, the NMR technique used in this study provided an intuitive basis for the analysis of water distribution and variation in F. lonicerae at different flowering stages.
