Design and test of the debearding device for Polygonatum

Polygonatum is one of the perennial herbs in Chinese medicine, thus leading to a high-value understory crop in agroforestry systems in China. The principal medicinal component can also share the substantial nutritional and therapeutic value. Since the fibrous roots with the inferior nutrition can often interfere with downstream processing, the debearding can serve as the essential preprocessing. However, conventional mechanical debearding cannot fully meet the scalable demand in the ever-growing industry, due to the technical constraints, such as the throughput, root removal, and physical damage to rhizomes. In this study, a horizontal hexagonal-tumbling debearding device was developed to integrate with the “drying pretreatment followed by mechanical brushing” technology. Several components are included during Polygonatum processing: a rigid frame, support rollers, an independent cage driving system with motor, a hexagonal rotating cage, an internal counter-rotating Stripping roller assembly with its dedicated drive, a removable collection bin, a protective dust cover, and a sliding door for operational convenience. Furthermore, the hexagonal cage and the internal Stripping rollers were simultaneously yet oppositely rotated to combine the tumbling, impacting, and brushing action on the rhizomes during operation. Fibrous roots were effectively detached to minimize the structural injury in the valuable rhizome tissue. A dynamic analysis was also conducted on the architecture and operation under motion and force interaction of Polygonatum within the drum. A systematic investigation was conducted to determine the parameters for high debearding efficiency with low product damage. A three-factor, three-level Box-Behnken response surface design was employed to optimize the performance of the device, with cage speed, stripping roller speed, and feed rate as independent variables, while shedding rate and breakage rate as the key response metrics. Statistical analysis of variance demonstrated that both cage speed and stripping roller speed exerted a highly significant influence on the debearding rate, while the feed rate also presented a significant correlation. In contrast, none of the three factors showed a statistically significant impact on the breakage rate within the tested ranges, indicating the effectiveness with minimal damage. Subsequently, response surface analysis further quantified the interactions among these parameters. Their combinations non-linearly influenced the outcome variables. Numerical optimization identified the ideal operational regime as a cage speed of 6 r/min, a stripping roller speed of 90 r/min, and a feed rate of 7.5 kg/min. The prediction models forecasted a shedding rate of 97.04% and a breakage rate of only 0.96% under the optimal parameter set. Triplicate tests were conducted to validate the average shedding rates of 96.83% and the breakage rate of 1.04%. There was excellent consistency with predictions after optimization. The results indicated that the newly developed device significantly outperformed conventional debearding machinery after assessment, in terms of both processing effectiveness and product integrity. Preprocessing quality and efficiency were enhanced in the supply chain, thereby supporting the sustainable scaling, value-added processing, and overall competitiveness of the Polygonatum industry. The findings can provide a solid scientific foundation and practical engineering insights for the specialized, efficient, and gentle processing equipment for Polygonatum and analogous medicinal rhizomes. A valuable framework with pretreatment, mechanical design, dynamic modeling, and optimization can offer for similar technologies in the post-harvest processing of agricultural and medicinal products.