[Drying kinetics and quality changes of Polygonati Rhizoma processed by nine cycles of steaming and sun-drying under...

The drying characteristics of Polygonati Rhizoma processed by nine cycles of steaming and sun-drying were studied, and the drying kinetics model was established. The effects of different drying temperatures on the quality changes of Polygonati Rhizoma decoction pieces during steaming and drying were further analyzed to clarify the drying mechanism, providing data for the processing technology of nine cycles of steaming and sun-drying for Polygonati Rhizoma. The drying kinetics model of Polygonati Rhizoma processed products was established at 60, 70, and 80 ℃. Using LF-NMR/MRI, the changes in water phase state and water distribution of Polygonati Rhizoma processed products during the processing were analyzed. The effective diffusion coefficient of water was calculated according to Fick's diffusion law. AHP-CRITIC mixed weighting method was applied to comprehensively evaluate the quality of Polygonati Rhizoma processed products at different drying temperatures based on the content of Polygonati Rhizoma polysaccharides, 5-hydroxymethylfurfural, polygonatine A, and extract. The results showed that the Page model could accurately describe the change in water content of Polygonati Rhizoma processed products. The effective diffusion coefficient of water ranged from 9.89 × 10~(-8) to 2.03 × 10~(-7) m~2·s~(-1). The T_2 spectrum revealed significant changes in the water phase state of Polygonati Rhizoma processed products. As the number of steaming cycles increased, the total water content decreased, the degree of water freedom reduced, and free water gradually transformed into bound water. The higher the temperature, the lower the water content of the decoction pieces. MRI monitoring showed that moisture in the Polygonati Rhizoma processed products gradually decreased from the outside to the inside with increasing steaming cycles. Based on the comprehensive evaluation results of Polygonati Rhizoma polysaccharides, 5-hydroxymethylfurfural, polygonatine A, and extract content, it was concluded that the four-cycle-steamed, 70 ℃ dried Polygonati Rhizoma decoction pieces have good quality. This study used drying kinetics combined with LF-NMR/MRI to quantify the changes and distribution of moisture during the drying process of Polygonati Rhizoma processed products. The changes in Polygonati Rhizoma polysaccharides, 5-hydroxymethylfurfural, polygonatine A, and extract content were studied, providing a scientific basis for elucidating the drying mechanism and drying process of Polygonati Rhizoma processed products.