Pulsed vacuum drying of Chinese ginger (Zingiber officinale Roscoe) slices: Effects on drying characteristics, rehydration ratio, water holding capacity, and microstructure

Effects of vacuum pressure duration (t-VPD of 5, 10, 15, and 20 min), ambient pressure duration (t-APD of 3, 5, 7, and 9 min), drying temperature (60, 65, 70, and 75 degrees C), and slice thickness (3, 5, 7, and 9 mm) on drying kinetics, rehydration ratio (RR), water holding capacity (WHC), and microstructure of Chinese ginger were investigated using a pulsed vacuum dryer. Various parameters affecting drying rate significantly of ginger slices except t-APD, and the shortest drying time of 300 min was obtained when the t-VPD, drying temperature, and slice thickness were 10 min, 70 degrees C, and 3 mm, respectively. Weibull model fitted the experimental results better (R-2 > 0.99) than first-order model. RR was increased with increasing of t-VPD while it was decreased with increasing of temperature, and a decreased trend of WHC was observed with increasing temperature or t-VPD. Microstructure observation indicated that increased t-VPD resulted in larger tunnel structure, and high temperature caused the formation of rigid structure, which well explained the changes of RR and WHC of dried ginger. The findings in current work contribute to good understanding of the pulsed vacuum drying behavior and quality of ginger.