Enhancing Okra Drying Quality and Efficiency Through Combined Freeze and Pulsed Spouted Microwave Vacuum Drying

Freeze drying (FD) is known for providing high-quality products but with low efficiency. To address this issue, this study explores the combination of FD and pulsed spouted microwave vacuum drying (PSMVD) for drying okra. The effect of applying PSMVD before (PSMVD-FD) or after (FD-PSMVD) FD on the quality, physicochemical properties, and microstructure of okra was investigated. Compared to FD alone, the combined drying reduced the drying time by 51.4-82.1%. The Weibull model was identified as the most suitable for the rehydration process of dried okra among the four models evaluated. Products from FD and combined drying exhibited higher rehydration capacity, chlorophyll content, and antioxidant capacity than other drying methods. PSMVD-FD resulted in the highest total phenol content (3.370 +/- 0.014 mg GAE/g). FTIR revealed that the combined dried okra had no production of new functional groups. Additionally, combined drying products minimized color change, maintained brittle texture, and preserved porous structure. Overall, the combined drying methods enhanced the efficiency of FD while maintaining the substantial product quality.