果蔬微波真空干燥（MVD）技术研究进展

为了提高甘薯干燥效率和改善产品品质，本文采用微波真空干燥（MVD）技术，研究了超声处理（US）、渗透脱水（OD）、超声辅助渗透（USOD）、真空辅助渗透（VAOD）和超声/真空辅助渗透（VUOD）对甘薯切片干燥动力学、微观结构、孔隙特征及理化性质的影响。采用Weibull分布函数和Dincer模型对干燥曲线进行拟合，并结合尺度参数（α）、形状参数（β）、滞后因子（G）、干燥系数（S）、毕渥数（Bi）探讨了MVD甘薯切片干燥过程的热、质传递机制。结果表明：相比其他处理，USOD和VUOD可显著提高甘薯切片的水分流失率（WL）和固形物增加率（SG）（P<0.05）。Weibull分布函数和Dincer模型对MVD甘薯切片的干燥曲线具有较好的拟合效果。模型参数（α, β, G, S）结果表明，经USOD处理的MVD甘薯切片干燥效率最高，加速阶段历时最短；毕渥数（Bi）处于0.243~3.617之间，表明MVD干燥过程甘薯切片温度变化由内部传导热阻和表面对流热阻共同控制。基于Weibull和Dincer模型计算获得的水分扩散系数D_cal和D_eff分别为7.986×10⁻⁸~1.249×10⁻⁷和1.508×10⁻⁸~8.272×10⁻⁸ m²/s，且均是USOD样品最大，OD最小。USOD和VUOD甘薯切片呈现蜂窝状、多孔结构，其中VUOD样品孔隙率最大（为33.30%），而USOD样品平均孔径最小（仅为164.50 nm）、迂曲度最大（为41.97）。相比其它预处理，USOD和VUOD处理显著提升了MVD甘薯切片的复水性能（P<0.05），降低了体收缩率，较好地保持了原有色泽，缩小了色差。研究结果可为甘薯切片的微波真空干燥条件筛选和品质调控提供参考。

Effects of pretreatment and drying methods on the quality and stability of dried sweet potato slices during storage

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.