Effects of Different Fixation Methods on Volatile Organic Compounds in Fresh Leaves of ‘Qiancha No.1’ Tea

Abstract

To explore the most suitable fixation method for the study of volatile organic compounds in fresh tea leaves, this study compared the effects of five fixation methods-steam fixation, hot air fixation, microwave fixation, vacuum freeze fixation, and liquid nitrogen fixation-on the volatile components of ‘Qiancha No.1’ tea shoots with one bud and two tender leaves as analyzed using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS). A total of 73 volatile organic compounds were identified, including 23 alcohols, 14 esters, 10 aldehydes, 15 alkenes, 4 ketones, and 7 others, with alcohols being the most abundant ones. A total of 16 volatile compounds were found to be common to the five fixed samples. Vacuum freeze fixation resulted in the highest number (43) and amount (112.93 mg/L) of volatile organic compounds, retaining higher alcohol contents. Liquid nitrogen fixation retained more esters, aldehydes, and alkenes, while steam fixation retained higher contents of other volatile organic compounds. Microwave fixed samples contained more alkenes. Hot air fixation was the least effective, retaining only 37 volatile organic compounds at the lowest concentration of 29.42 mg/L. Multivariate statistical analysis showed that while hot air and microwave fixed samples shared high similarity in volatile organic compounds, the other fixation methods resulted in significant differences in volatile organic compounds. A total of 25 volatile organic compounds, such as cedrene and 2-nonanone, were identified as markers to differentiate among these fixation methods. Vacuum freeze fixation was able to retain the volatile organic compounds in fresh tea leaves to a greater extent.

Keywords

• ‘qiancha no.1’; fixation method; headspace solid-phase microextraction; gas chromatography-mass spectrometry; volatile organic compounds