Influence of drying methods on volatile components of Flammulina velutipe

The volatile composition of Flammulina velutipe by different drying methods (heat pump, hot air and vacuum freeze drying) was analyzed by gas chromatography-mass spectrometry (GC-MS) with solid-phase micro-extraction (SPME) . A total of 54 volatile compounds were detected. By using heat pump and hot air drying, aldehydes and alcohols were the major components in Flammulina velutipe, followed by esters and ketones. Higher relative content of 2/3-methylbutanal and 2, 3-butanediol were observed in the sample by using heat pump, while 3-methylbutanal and butyrolactone were in greater percentage in the one by hot air drying method. On the other hand, hydrocarbons and alcohols showed the highest contents in the sample by vacuum freeze drying method and the control. It demonstrated that 2, 2, 4, 6, 6-pentamethylheptane, 2, 3-butanediol and D-limonene were the major components in the sample by vacuum freeze drying method.Among these drying methods, more volatile compounds which had lower thresholds were generated by heat treatment methods due to the interaction of compounds in raw material. Besides, pyrazines were detected by hot air drying for local heat reactions. With regard to vacuum freeze drying method, the fresh Flammulina velutipe flavor could be better kept due to the low temperature and anaerobic condition.