Effects of Ultrasound/Vacuum-Assisted Osmotic on the Kinetics and Physicochemical Properties of Sweet Potatoes Dried by Microwave Vacuum

The effects of ultrasonic treatment (US), osmotic dehydration (OD), ultrasonic-assisted osmosis (USOD), vacuum-assisted osmosis (VAOD), and ultrasonic/vacuum-assisted osmosis (VUOD) on the drying kinetics, microstructure, pore characteristics, and physicochemical properties of sweet potatoes were studied using microwave vacuum drying technology to improve drying efficiency and product quality. Weibull distribution function and Dincer model were used to fit the drying curves, and the heat and mass transfer mechanisms of the drying process of MVD sweet potato slices were investigated by combining the scale parameter (α), shape parameter (β), hysteresis factor (G), drying coefficient (S) and Biovor number (Bi). The findings demonstrated that when compared to other pre-treatments, USOD and VUOD significantly enhanced the water loss (WL) and solids gain (SG) of sweet potato slices (P<0.05). The drying curves of the MVD sweet potato slices were perfectly fitted by the Dincer model and Weibull distribution function. The MVD sweet potato slices pretreated by USOD had the maximum drying efficiency and the shortest acceleration phase, according to the findings of the model parameters (α, β, G, S). The Biovor number (Bi), which ranged from 0.243 to 3.617, indicated that internal conduction heat resistance and surface convection heat resistance jointly regulated the temperature changes of sweet potato slices during MVD drying. According to the Weibull and Dincer model, the moisture diffusion coefficients D_cal and D_eff were maximal for USOD samples and minimum for OD samples, ranging from 7.986×10⁻⁸ to 1.249×10⁻⁷ m²/s and 1.508×10⁻⁸ to 8.272×10⁻⁸ m²/s, respectively. The MVD sweet potato slices pretreated by USOD and VUOD showed regular cellular structure with a honeycomb porous structure. The VUOD sample had the maximum porosity (33.30%), whereas the USOD sample had the smallest average pore size (164.50 nm) and the largest tortuosity (41.97). In comparison to other pretreatments, USOD and VUOD treatments considerably enhanced the rehydration performance of MVD sweet potato slices (P<0.05), decreased bulk shrinkage, better preserved the original color, and lowered the color difference. The study's findings could serve as a guide for selecting and evaluating the microwave vacuum drying parameters for sweet potato slices.