Effect of steam pretreatment on drying kinetics and quality of Polygonati Rhizoma dried in hot-blast air

Polygonati Rhizoma, an edible herb, is used in Chinese medicine and also in functional foods. In this study, a kinetic model for drying Polygonati Rhizoma in hot-blast air was established for different temperatures (40, 60, and 80 degrees C) and slice thicknesses (4, 6, and 8 mm). Low field nuclear magnetic resonance and magnetic resonance imaging were applied simultaneously to record the migration and distribution of water in the Polygonati Rhizoma slices during the hot-blast air drying. After combining these data with measurements of color parameters and polysaccharide content, the best conditions for drying Polygonati Rhizoma were determined. The Page model accurately predicted the drying process. The magnetic resonance imaging results demonstrated that the moisture in Polygonati Rhizoma diffused from the interior to the exterior during drying. The T-2 data from low field nuclear magnetic resonance indicated three states of water in the Polygonati Rhizoma: bound, immobile, and free. Compared with slices of the raw material that were dried directly, steamed samples with a thickness of less than 6 mm exhibited a better color, higher polysaccharide content, and faster water loss using a drying process at 60 degrees C. Practical Applications Various processing procedures are available to reduce moisture in foods to extend their storage life and control their quality. The high contents of polysaccharides and water in the fresh food make it easily susceptible to rotting if not rapidly processed. The present study discusses the effect of steam pretreatment on the kinetics and quality of Polygonati Rhizoma dried in hot-blast air. Using color and polysaccharide content as an index of quality, Polygonati Rhizoma processed using 60 min of steaming followed by drying at 60 degrees C produced the best quality. This combination of processing conditions enhanced the drying rate while maintaining the color and polysaccharide content. These results could also be used as a technical basis for the post-harvest processing of Polygonati Rhizoma and similar agricultural products.