Ultrasound and Freeze–Thaw Pretreatments Alter Cell Wall Structure and Water Status to Improve Vacuum Freeze‐Drying Efficiency and Quality Attributes of Plums

Plums ( Prunus domestica L.) are valued for their flavor and nutritional properties; however, their preservation through vacuum freeze‐drying (VFD) is often characterized by long processing times and high energy consumption. This study investigated the effects of ultrasound (US), freeze–thaw (FT), and their combinations—US followed by freeze–thaw (US+FT) and US‐assisted thawing (US‐T)—as pretreatments to enhance VFD efficiency and product quality. Pretreatment effects on cell wall structure, polysaccharide composition (pectin, cellulose, and hemicellulose), water status, drying kinetics, total energy consumption (TEC), and final product quality were systematically evaluated. All pretreatments, particularly those involving FT, significantly altered cell wall integrity, increased water‐soluble pectin, and enhanced water mobility, quantitatively defined as the water status, which was characterized by longer T 22 and T 23 relaxation times and a significant redistribution of water from less mobile to more mobile populations. These microstructural and water status changes contributed to improved drying performance; compared to the control, US‐T and US+FT reduced VFD time by up to 28.4% and 15.4%, and TEC by 27.0% and 15.2%, respectively. While all pretreatments improved rehydration capacity and texture, US‐T achieved the shortest drying time (21.9 h) and the lowest TEC (69.17 kWh/kg), while most effectively retaining color (higher L * value), total phenolic content, vitamin C, and antioxidant capacity (DPPH and FRAP). Electronic nose analysis further confirmed that US‐T samples exhibited the most desirable aroma profile. These results demonstrate that US‐T is a promising nonthermal pretreatment strategy that significantly enhances VFD efficiency and the overall quality of dried plums by favorably modulating cell wall structure and water distribution.