Effects on volatile oil and volatile compounds of Amomum tsao-ko with different pre-drying and drying methods

The influences of different pre-drying (boiling water treatment for 2 min, 5 min and 10 min, microwave heating at 500 W, oven heating at 105 °C) and drying methods (air drying, sun drying, oven drying at 50 °C, microwave drying at 150 W, freeze drying at −50 °C, electric baking drying at 50 °C and smoke drying) on the quality of Amomum tsao-ko were studied. Volatile oil (VO) and volatile compounds of A. tsao-ko were analyzed using gas chromatography and mass spectrometry (GC-MS) and near infrared reflectance spectroscopy (NIRS). Results demonstrated that pre-drying, air drying and sun drying caused mildew on the fruit, while boiling water and microwave radiation at 500 W or 150 W caused cracking on the fruit. Correlation analysis showed that the fruit cracking rate and the fruit mildew rate were significantly and negatively correlated with the VO content. Additionally, different drying methods dramatically impacted the VO content and main components (1,8-cineole, alpha-phellandrene, (E)-2-decenal, alpha-methylcinnamaldehyde, nerolidol, alpha-pinene, (E)-citral, (Z)-citral, 4-indanecarbaldehyde, (E)-2-dodecenal, linalool and beta-pinene). The highest VO amount was achieved obtained in sun drying and electric baking drying at 50 °C, and the higher VO amount was also obtained by pre-drying with oven heating at 105 °C, air drying, oven drying at 50 °C, and smoke drying. This study provided reference basis for the selection of drying, processing methods and final products of A. tsao-ko.