Quality evaluation of rotary microwave vacuum drying of Codonopsis pilosula based on CRITIC weight-TOPSIS method

Abstract

In this study, the parameters of drying temperature, slice thickness, and vacuum level were selected as experimental variables to assess their impact on the drying characteristics, quality, and microstructure of Codonopsis pilosula slices through rotary microwave vacuum drying (RMVD). Furthermore, the CRITIC weight-TOPSIS method was employed to identify the optimal drying conditions. The results indicated that within a specific range, elevating the drying temperature and vacuum level, alongside reducing the slice thickness, markedly decreased the drying duration for the samples. The slice thickness exerted a substantial influence on the Deff, with Deff values ranging from 0.659 × 10−7 m2/min to 1.229 × 10−7 m2/min at different drying conditions. Moreover, the drying temperature exhibited the most prominent influence on the total flavonoid content, total phenol content, and antioxidant activity. The RMVD contributes to enhancing the content of syringin, lobetyolin, and atractylenolide III. In particular, a slice thickness of 3 mm to 4 mm and a drying temperature between 45 °C and 50 °C are favorable drying parameter ranges for the atractylenolide III. Enhancing the vacuum, reducing the slice thickness, and lowering the drying temperature were observed to better preserve the color of the Codonopsis pilosula slices. Microstructural observations revealed that samples subjected to low vacuum levels, larger slice thicknesses, and lower drying temperatures exhibited more pronounced internal honeycomb pore structures, as well as lower levels of shrinkage and fragmentation. Additionally, the correlation heat map illustrated a significant association between antioxidant activity and total phenol content, while the changing trend of brightness and red-greenness was linked to the content of syringin and atractylenolide III, respectively. Under the current experimental conditions, the drying temperature of 45 °C, slice thickness of 4 mm, and vacuum level of −0.070 MPa were determined as the optimal combination of drying parameters. Overall, the use of RMVD has proven to enhance the overall quality of dried Codonopsis pilosula slices.