Headspace volatiles and physical characteristics of vacuum-microwave, air,and freeze-dried oregano (Lippia berlandieri Schauer)

Mexican oregano (Lippia berlandieri Schauer) was dried using a freeze drier , conventional hot air drier, and a recently developed vacuum-microwave dri er. The effect of the drying method on the relative content of major flavor volatiles, rehydration rate, color, and structural integrity of the herb w as evaluated. Dynamic headspace analysis of volatiles present in fresh or d ried oregano revealed that beta -myrcene, alpha -terpinene, gamma -terpinen e, p-cymene, and thymol were the major volatile compounds of the plant. The level of thymol in vacuum-microwave-dried oregano was found to be comparab le to that of fresh or freeze-dried samples (1.3 times the thymol concentra tion of air-dried). Air-dried samples of oregano were darker, were less gre en, and exhibited lower rehydration rates than those prepared by vacuum-mic rowave or freeze-drying. Structures of vacuum-microwave and freeze-dried or egano appeared to be quite similar as observed on electron micrographs.