Effects of vacuum ultrasonic infiltration and combined drying on rehydration quality of ginger (Zingiber officinale Roscoe)

Ginger is susceptible to deterioration during storage, drying is an efficient approach to extend its shelf life. This research mainly aimed to investigate the effects of different osmotic pretreatments (NaCl solution osmotic (NOD), ultrasonic-assisted NaCl solution osmotic (UOD) and vacuum combined ultrasonic-assisted NaCl solution osmotic (VUOD)) and vacuum freeze-drying combined with hot air drying (FAD) on the drying time, rehydration ability, and physical and chemical properties of rehydrated ginger slices. Compared with single vacuum freeze-drying (VFD), vacuum combined with ultrasonic-assisted infiltration vacuum freeze-drying combined with hot air drying (VUOD-FAD) shortened the drying time by 59.75%. Rehydrated ginger treated with VUOD-FAD had a lower total color difference (5.65), and higher rehydration rate (4.89), with an odor that closer to the fresh sample's odor. Compared with the fresh sample, the chemical properties of the rehydrated samples had changed greatly. Compared with the rehydrated samples treated with VFD, FAD samples had higher gingerol content, 6-gingerol content, total phenol content (TPC), total flavonoids content (TFC), and oxidation resistance. It can be concluded that the processing method of VUOD-FAD is better than the other methods.