Abstract
Astragali Radix (Huangqi) is an important herb medicine that is always processed into pieces for clinical use. Many operations need to be performed before use, among which drying of Astragali Radix (AR) pieces is a key step. Unfortunately, research on its drying mechanism is still limited. Low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) techniques were applied to study the moisture state and distribution during drying. The content of bioactive components and texture changes were measured by HPLC and texture analyzer, respectively. The moisture content of the AR pieces decreased significantly during drying, and the time to reach the drying equilibrium were different at different temperatures. The time when at 70°C, 80°C, and 90°C reach complete drying are 180 min, 150 min and 120 min, respectively. 80°C was determined as the optimum drying temperature, and it was observed that the four flavonoids and astragaloside IV have some thermal stability in AR pieces. When dried at 80°C, although the total water content decreased, the free water content decreased from 99.38% to 15.49%, in contrast to the increase in bound water content from 0.62% to 84.51%. The texture parameters such as hardness changed to some extent, with the hardness rising most significantly from 686.23 g to 2656.67 g. Correlation analysis revealed some connection between moisture content and LF-NMR and texture analyzer parameters, but the springiness did not show a clear correlation with most parameters. This study shows that HPLC, LF-NMR, MRI, and texture analyzers provide a scientific basis for elucidating the drying principles of AR pieces. The method is useful and shows potential for extension and application; therefore, it can be easily extended to other natural herb medicines.
Highlights
Processing, known as Paozhi in Chinese, is a unique Chinese pharmaceutical technique with a long history of facilitating the use of Chinese herbal medicines for specific clinical needs based on traditional Chinese medical theory [1]
Astragali Radix (Huangqi in Chinese) originates from the dried root of Astragalus membranaceus (Fisch.) Bge. var. mongholicus (Bge.) Hsiao or Astragalus membranaceus (Fisch.) Bge., which has been used as traditional Chinese medicine (TCM) for more than 2,000 years [5]
Compared with the drying time required at 70 ̊C, those at 80 ̊C and 90 ̊C were 16.67% and 33.33% less, respectively
Summary
Processing, known as Paozhi in Chinese, is a unique Chinese pharmaceutical technique with a long history of facilitating the use of Chinese herbal medicines for specific clinical needs based on traditional Chinese medical theory [1]. Traditional Chinese medicine decoction pieces, known as Yinpian in China, are important processed product that is directly applicable for clinical use [2]. The dried medicinal materials in production are removed from impurities, cleaned, moistened, cut and dried, and different decoction pieces are made . The process of producing AR decoction pieces is to ’’remove impurities, separate size, clean, moisten, cut thick pieces and dry [15].’’ At present, research reports on the drying of AR decoction pieces are shallow and mainly use appearance, shape and other indicators to pursue an optimum drying process. Low-field nuclear magnetic resonance (LF-NMR), magnetic resonance imaging (MRI) and texture analyzers have obvious advantages in detecting moisture migration, distribution and transformation and texture changes
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