Effects of ultrasonic-assisted microwave vacuum drying on physicochemical, nutritional, and quality of dried lotus seeds (Nelumbo nucifera Gaertn.)

Ultrasonic-assisted microwave vacuum drying represents a promising technique for enhancing the quality of agricultural products. This study evaluates the effects of four drying techniques—hot air drying (HAD), microwave vacuum drying (MVD), airborne ultrasonic combined with microwave vacuum drying (USMVD), and waterborne ultrasonic pretreatment combined with microwave vacuum drying (US + MVD)—on the quality of lotus seeds. Results indicate that USMVD significantly improves product quality by lowering water activity to 0.38-0.45, increasing levels of slowly digestible and resistant starch, and boosting antioxidant capacity by up to 18.2% compared to traditional MVD. It also improves physical properties, reducing hardness by 20-54%, decreasing shrinkage, and better preserving color ( ΔE reduction of 3.38-5.88%), while enhancing rehydration. Microstructural analysis suggests that USMVD better maintains cell structure and creates porous networks, explaining the improvements in quality. Principal component analysis revealed that the USMVD treatment was significantly correlated with excellent quality characteristics. Overall, these findings confirm that USMVD is an advanced drying method that combines ultrasonic and microwave-vacuum techniques to produce high-quality dried lotus seeds with improved functional and nutritional qualities.