Comparison of Potato Void Structures Dried by Air-Drying, Freeze-Drying, and Microwave-Vacuum-Drying, and the Physical Properties of Powders After Grinding

Powders manufactured from dried fruits and vegetables have wide applicability in the food industry. In this study, we focused on the structure of materials dried by different processes and its relationship to the physical properties of powders after grinding using potato samples. Air-dried (AD) samples showed significant shrinkage, while the interior of those dried by microwave-vacuum-drying (MVD) tended to be more porous, especially when pre-frozen, and showed a fine void structure similar to that with freeze-drying (FD). The particle size of powders obtained by grinding dried samples was coarse for AD-derived powders and fine and uniform for FD-derived powders, which showed the finest pore structure, followed closely by the pre-frozen MVD powder. The FD sample produced a fine, highly uniform powder; however, it required the longest drying time, while the pre-frozen MVD sample needed the shortest drying time. Therefore, in the context of drying efficiency and powder quality, the pre-frozen MVD technique has several advantages and can effectively dry potato samples. Although finer powders have advantages in terms of improved physicochemical properties, powders with smaller particles exhibit lower flowability; in this study, the FD-derived powder showed the lowest flowability. The present study suggests that the more porous the structure of the dried material with fine voids, the finer the powder after grinding.