Unlocking new drying potential for Lotus root: Ultrasonic osmotic dehydration and microwave hot air drying based on phenolic retention and microstructure

Unlocking the potential of advanced drying techniques is crucial for enhancing the quality and shelf life of lotus root. This study investigated the impact of Ultrasonic-assisted osmotic dehydration (USOD) on the drying process and quality characteristics of lotus root using penetrating microwave hot air fluidized bed drying (PMHAD). The results indicate that USOD pretreatment (55 °C, 30 min) reduced the moisture content of lotus root by 18.4 %, with PPO and POD activities reduced to 34.7 % and 62.9 %, respectively. Compared to the unpretreated group, this pretreatment preserved the cell compactness of lotus root, thereby preventing the loss of phenolic compounds (increased by 9.1 %) and antioxidant activity (increased by 13.9 %). Morphological analysis of cell structure further revealed that changes in TPA parameters, shrinkage rate, and rehydration rate were closely associated with cell structure compactness. For samples subjected to USOD pretreatment, increasing microwave power during PMHAD induced microstructural changes in the cells. At a microwave power of 1.5 W/g, the maximum cell equivalent diameter reached 54.12 μm, while cell compactness decreased to 0.855, and relative crystallinity dropped to 16.86, leading to the loss of intracellular and thermosensitive substances. Principal component analysis highlighted the extent of damage and trend changes observed during the lotus root drying process.