Effect of different drying methods on the quality of Rugao black pakchoi

Objective: This study aimed to investigated the effect of ice-temperature vacuum drying on the powder quality of selenium-rich Rugao black pakchoi. Methods: After pretreatment, the fresh black pakchoi was dried to the moisture content of (5.0±0.5) %, and the physical and chemical indexes were investigated, comparing to the control groups of hot-air drying, vacuum drying and freeze-vacuum drying. Results: The vitamin C content of vacuum drying at ice temperature was 554.60 mg/100 g, and the retention rate reached 83.96%, which was 43.11%, 33.57% and 1.61% higher than that of hot-air drying, vacuum drying and freeze-vacuum drying, respectively. Glutathione peroxidase had little activity loss and the best purity maintenance. The retention rates of total phenols and total flavonoids were 59.69% and 60.58%, respectively, which were better than the other three groups. In terms of microstructure, the powder of ice-temperature vacuum drying group was well-distributed, with a smooth and flat surface and less debris. Compared with the other three groups, the ice-temperature vacuum drying group could maintain the original dark green color, and the rehydration and solubility were improved. Conclusion: The ice-temperature vacuum drying process can minimally affect the Rugao black pakchoi powder, and the nutritional quality of this powder is the highest.