Hot Air Impingement Drying Enhanced Drying Characteristics and Quality Attributes of Ophiopogonis Radix

The effects of drying temperature and air velocity on the drying characteristics, color, bioactive compounds, rehydration ratio, and microstructure of Ophiopogonis Radix during hot air impingement drying (HAID) were explored in the current study. The experimental results showed that the drying temperature and air velocity had a significant impact on the drying characteristics and quality attributes of dried products except for the rehydration ratio. The drying time decreased from 720 to 240 min with the increase of drying temperature from 50 to 70 °C. Increasing the air velocity from 6 to 12 m/s enhanced the drying process of Ophiopogonis Radix, while the extension of air velocity to 15 m/s lowered the drying rate. The samples that were dried at a lower drying temperature obtained lower color difference. Properly increasing the drying temperature or air velocity could increase the total polysaccharide and flavonoid contents of dried products. Additionally, a back-propagation neural network (BPNN) model was developed to predict the moisture ratio of Ophiopogonis Radix during the drying process. The optimal BPNN with 3-11-1 topology were obtained to predict the moisture ratio of Ophiopogonis Radix during HAID and performed with an acceptable performance.