Effect of drying methods on volatiles of Chinese ginger (Zingiber officinale Roscoe)

Fresh ginger slices were dehydrated by air drying (AD), microwave drying (MD), vacuum drying (VD), and freezing drying (FD). Volatiles were extracted from fresh ginger pulp and dried ground ginger powder with solid-phase microextraction (SPME), and identified by gas chromatography-mass spectrometry (GC-MS). Results indicated that, 19, 28, 21, 20, 31 and 20 novel compounds (70 in total) appeared in dried gingers treated by AD at 50, 60 and 70 degrees C, MD at 60W, VD in 13.3 kPa at 60 degrees C and FD in 0.203 kPa at chamber temperature of 22 degrees C, respectively. Principal component analysis for the main volatiles indicated that drying increased the relative contents of benzene,1-(1,5-dimethyl-4-hexenyl)-4-methyl-, 1,3-cyclohexadiene,5-(1,5-dimethyl-4-hexenyl)-2-methyl-,[S-(R*,S*)]-, alpha-farnesene and cyclohexene,3-(1,5-dimethyl-4-hexenyl) -6-methylene-,[S-(R*,S*))- while decreased those of 2,6-octadienal,3,7-dimethyl-,(Z) and 2,6-octadienal,3,7-dimethyl-. Cluster analysis disclosed that MD was the most favorite drying way, followed by AD at 60 degrees C, VD, FD, and AD at 50 and 70 degrees C. (C) 2011 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.